Household Wiring FAQ

Part 1 of 2

  • From: (Chris Lewis)

    Last-modified: Mon Nov 14 01:10:37 EST 1994
    	    Frequently Asked Questions on Electrical Wiring
                            Copyright 1991, 1992, 1993
    		Steven Bellovin (
    		Chris Lewis (
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    The latest FAQ can always be obtained from:
    Answers to many other topics related to houses can be obtained from the archive; send an empty piece of mail to for information.
    Changes to previous issue marked with "|" in left column.  Watch
    particularly for "NEW" in the Questions list for new or substantively
    changed answers.  
    Subject: Questions answered in this FAQ
    	What is the NEC?  Where can I get a copy?
    	What is the CEC?  Where can I get a copy?
    	Can I do my own wiring?  Extra pointers?
    	What do I need in the way of tools?
    	What is UL listing?
    	What is CSA approval?
    	What impact does NAFTA have on wiring standards and approvals?
    	Are there any cheaper, easier to read books on wiring?
    	Inspections how and what?  Why should I get my wiring inspected?
    	My house doesn't meet some of these rules and regulations.
    	A word on voltages: 110/115/117/120/125/220/240
    	What does an electrical service look like?
    	What is a circuit?
    	"grounding" versus "grounded" versus "neutral".
    	What does a fuse or breaker do?  What are the differences?
    	Breakers?  Can't I use fuses?
    	What size wire should I use?
    	Where do these numbers come from?
    	What does "14-2" mean?
    	What is a "wirenut"/"marrette"/"marr connector".  How are they used?
    	What is a GFI/GFCI?
    	Where should GFCIs be used?
    	Where shouldn't I use a GFCI?
    	What is the difference between a GFCI outlet and a GFCI breaker?
    	What's the purpose of the ground prong on an outlet, then?
    |	Grounding electrode system (NEW)
    |	Bonding requirements (NEW)
    |	Testing grounding conductors and grounding electrodes. (NEW)
    	Why is one prong wider than the other?  Polarization
    |	How do I convert two prong receptacles to three prong?
    	Surges, spikes, zaps, grounding and your electronics
    	Are you sure about GFCIs and ungrounded outlets?
    	    Should the test button work?
    	What kind of outlets do I need in a kitchen?
    	Where must outlets and switches be in bathrooms?
    	General outlet placement rules/line capacities
    	What is Romex/NM/NMD?  What is BX?  When should I use each?
    	Should I use plastic or metal boxes?
    	Junction box positioning?
    	Can I install a replacement fixture?
    	Noisy fluorescent fixtures, what do I do?
    	Noisy lights with dimmer switches, what do I do? (NEW)
    	What does it mean when the lights brighten when a motor starts?
    	What is 3 phase power?  Should I use it?  Can I get it in my house?
    	Is it better to run motors at 110 or 220?
    	What is this nonsense about 3HP on 110V 15A circuits?
    	How should I wire my shop?
    	Underground wiring
    	Doorbell/telephone/cable other service wiring hints
    	Aluminum wiring
    	I'm buying a house!  What should I do?
    	What is this weird stuff?  Old style wiring
    	Where do I buy stuff?
    	Copper wire characteristics table
    	Smoke detector guidelines
    Subject: Introduction/Disclaimers
    	Although we've done a fair bit of wiring, we are not
    	electricians, and we cannot be responsible for what you do.  If
    	you're at all uncertain about what is correct or safe, *don't
    	do it*.  Contact someone qualified -- a licensed electrician,
    	or your local electrical inspector.  Electricity is no joke;
    	mistakes can result in shocks, fires, or electrocution.
    	Furthermore, our discussion is based on the U.S. National
    	Electrical Code (NEC) and the Canadian Electrical code (CEC).
    	To the best of our abilities, we have confirmed every detail
    	with the electrical code, but we don't quote sections
    	simply to keep this thing readable.  If you think we're wrong,
    	we invite you to correct us, but please - quote references!
    	The NEC and the CEC do not, in and of themselves, have the
    	force of law.  Many municipalities adopt it en toto.  Others,
    	however, do not.  Check your with your local building
    	department (and  Hydro Inspection Offices in
    	Canada) to find out what applies in your area.  Also,
    	your local electrical utility may also have special requirements
    	for electrical service installation.  Bear in mind, too, that
    	we say here applies primarily to ordinary single-family
    	residences.  Multi-family dwellings, mobile homes, commercial
    	establishments, etc., are sometimes governed by different
    	Also note that, contrary to popular belief in the U.S. (and in
    	some parts of Canada), Canada is not a wholly-owned subsidiary
    	of the U.S.  Consequently, the NEC does not apply in Canada.
    	Lots of things are the same, including voltages, line
    	frequencies, and the laws of physics.  But there are a number
    	of crucial differences in the regulations.  Where we can, we've
    	noted them, flagging the relevant passages with ``NEC'' or
    	Remember that the CEC and NEC are minimal standards.  It is often
    	smart to go beyond their minimal requirements.
    Subject: What is the NEC?  Where can I get a copy?
    	The NEC is a model electrical code devised and published by the
    	National Fire Protection Association, an insurance industry group.
    	It's revised every three years.  The 1993 version has been released.
    	You can buy a copy at a decent bookstore, or by calling them directly
    	at 800-344-3555.  The code exists in several versions.  There's the
    	full text, which is fairly incomprehensible.  There's an abridged
    	edition, which has only the sections likely to apply to most houses.
    	And there's the NEC Handbook, which contains the ``authorized
    	commentary'' on the code, as well as the full text.  That's the
    	recommended version.  Unfortunately, there's no handbook for
    	the abridged edition.  And the full handbook is expensive --
    	US$65 plus shipping and handling.
    Subject: What is the CEC?  Where can I get a copy?
    	The Canadian Standards Association is an organization made up
    	of various government agencies, power utilities, insurance
    	companies, electrical manufacturers and other organizations.
    	The CSA publishes CSA Standard C22.1 which is updated every two
    	or three years.  Each province adopts, with some amendments,
    	this standard and publishes a province-specific code book.
    	Since each province publishes its own slightly modified
    	standard, it would be somewhat confusing to obtain the CSA
    	standard itself.  In this FAQ, "CEC" really means the
    	appropriate provincial standard.  In particular, this FAQ is
    	derived from the Ontario Hydro Electrical Safety Code, 20th
    	edition (1990).  Which is in turn based on CSA C22.1-1990 (16th
    	edition).  While differences exist between the provinces, an
    	attempt has been made to avoid specific-to-Ontario detail.
    	The appropriate provincial code can be obtained from electrical
    	inspection offices of your provincial power authority.  In
    	Ontario, it's Ontario Hydro.  The Ontario Hydro book isn't
    	overly fat.  It's about C$25, and includes mailed updates.  I
    	hear that these standards are somewhat easier to read than the
    	equivalent NEC publications.
    	Don't bother asking in Quebec - DIY wiring is banned throughout
    	the province.
    Subject: Can I do my own wiring?  Extra pointers?
    	In most places, homeowners are allowed to do their own wiring.
    	In some, they're not.  Check with your local electrical
    	inspector.  Most places won't permit you to do wiring on other's
    	homes for money without a license.  Nor are you permitted to do
    	wiring in "commercial" buildings.  Multiple dwellings (eg: duplexes)
    	are usually considered "semi-commercial" or "commercial".  However,
    	many jurisdictions will permit you to work on semi-commercial
    	wiring if you're supervised by a licensed electrician - if you can
    	find one willing to supervise.
    	If you do your own wiring, an important point:
    	Do it NEAT and WELL!  What you really want to aim for is a better
    	job than an electrician will do.  After all, it's your own home,
    	and it's you or your family that might get killed if you make
    	a mistake.  An electrician has time pressures, has the skills
    	and knows the tricks of the trade to do a fast, safe job.
    	In this FAQ we've consciously given a few recommendations that
    	are in excess of code, because we feel that it's reasonable,
    	and will impress the inspector.
    	The inspector will know that you're an amateur.  You have to
    	earn his trust.  The best way of doing this is to spend your
    	time doing as neat a job as possible.  Don't cut corners.
    	Exceed specifications.  Otherwise, the inspector may get extremely
    	picky and fault you on the slightest transgressions.
    	Don't try to hide anything from the inspector.
    	Use the proper tools.  Ie: don't use a bread knife to strip
    	wires, or twist wires with your fingers.  The inspector
    	won't like it, and the results won't be that safe.  And it
    	takes longer.  And you're more likely to stick a hunk of
    	12ga wire through your hand that way.
    	Don't handle house wire when it's very cold (eg: below -10C
    	or 16F).  Thermoplastic house wire, particularly older types
    	become very brittle.
    Subject: What do I need in the way of tools?
    	First, there's the obvious -- a hammer, a drill, a few
    	screwdrivers, both straight and Phillips-head.  If you're 
    	lucky enough to live in Canada (or find a source of CSA-approved
    	devices) you need Robertson ("square recess") screwdrivers
    	(#1 and #2) instead of phillips.
    	For drilling a few holes, a 3/4" or 1" spade bit and 1/4" or
    	3/8" electric drill will do.  If you're doing a lot, or
    	are working with elderly lumber, we recommend a 1/2" drill
    	(right-angle drills are wonderful.  Can be rented) and
    	3/4" or 1" screw-point auger drill bits.  These bits pull
    	you through, so they're much faster and less fatiguing, even
    	in 90 year old hardwood timbers.
    	Screw-driver bits are useful for drills, expecially if you
    	install your electrical boxes using screws (drywall screws
    	work well).
    	For stripping wire, use a real wire stripper, not a knife or
    	ordinary wire cutters.  Don't buy the $3 K-mart "combo stripper,
    	crimper and bottle opener" types.  You should expect to pay
    	$15 to $20 for a good "plier-type" pair.  It will have sized
    	stripping holes, and won't nick or grab the wire - it should
    	be easy to strip wire with it.  One model has a small hole in the
    	blade for forming exact wire loops for screw terminals.  There
    	are fancier types (autostrip/cut), but they generally aren't
    	necessary, and pros usually don't use them.
    	A pair of diagonal side cutter pliers are useful for clipping ends
    	in constricted places.  Don't use these for stripping wire.
    	You will need linesman pliers for twisting wires for wire nuts.
    	You should have a pair of needle-nose pliers for fiddling
    	inside boxes and closing loops, but it's better to form wire
    	loops with a "loop former hole" on your wire stripper - more
    	If you're using non-metallic cable, get a cable stripper for
    	removing the sheath.  Or, do what some pros do, they nick the
    	end of the sheath, grab the ground wire with a pair of pliers,
    	and simply rip the sheath back using the ground wire as a
    	"zipper", and cut the sheath off.  You shouldn't try to strip
    	the sheath with a knife point, because it's too easy to
    	slash the insulation on the conductors.  Apparently Stanley
    	utility knives fitted with linoleum cutters (hooked blades)
    	can be used to strip sheath, but there is still the possibility
    	that you'll gouge the conductors.
    	For any substantial amount of work with armored cable, it's well
    	worth your while to invest in a rotary cable splitter (~US$ 18).
    	Hack saws are tricky to use without cutting into the wire
    	or the insulation.
    	Three-prong outlet testers are a quick check for properly-wired
    	outlets.  About $6.  Multimeters tell you more, but are a lot more
    	expensive, and probably not worth it for most people.  A simple
    	voltage sensor, which can detect potential through an insulated
    	wire not supplying any devices, is extremely helpful; they cost
    	about US$ 10 at Radio Shack.
    	You should have a voltage detector - to check that the wires are
    	dead before doing work on them.  Neon-bulb version are cheap ($2-3)
    	and work well.  If you get more serious, a "audible alarm" type is
    	good for tracing circuits without a helper.  (Though I've been known
    	to lock the drill on, and hit breakers until the scream stops ;-)
    	For running wires through existing walls, you need fish tape.
    	Often, two tapes are needed, though sometimes, a bent hanger or
    	a length of thin chain will suffice.  Fish tapes can be rented.
    	Electrical tape.  Lots of it ;-)  Seriously, a good and competent
    	wiring job will need very little tape.  The tape is useful for
    	wrapping dicy insulation in repair work.  Another use is to wrap 
    	around the body of outlets and switches to cover the termination
    	screws - I don't do this, but drywall contractors prefer it (to
    	prevent explosions when the drywall knife collides with a live outlet
    	that has no cover plate).
    Subject: What is UL listing?
    	The UL stands for "Underwriters Laboratory".  It used to be
    	an Insurance Industry organization, but now it is independent
    	and non-profit.  It tests electrical components and equipment
    	for potential hazards.  When something is UL-listed, that means
    	that the UL has tested the device, and it meets their requirements
    	for safety - ie: fire or shock hazard.  It doesn't necessarily
    	mean that the device actually does what it's supposed to, just
    	that it probably won't kill you.
    	The UL does not have power of law in the U.S. -- you are
    	permitted to buy and install non-UL-listed devices.  However,
    	insurance policies sometimes have clauses in them that will
    	limit their liability in case of a claim made in response to
    	the failure of a non-UL-listed device.  Furthermore, in
    	many situations the NEC will require that a wiring component
    	used for a specific purpose is UL-listed for that purpose.
    	Indirectly, this means that certain parts of your wiring
    	must be UL-listed before an inspector will approve it and/or
    	occupancy permits issued.
    Subject: What is CSA approval?
    	Every electrical device or component must be certified by the
    	Canadian Standards Association (or recognized equivalent) before
    	it can be sold in Canada.  Implicit in this is that all wiring
    	must be done with CSA-approved materials.  They perform testing
    	similar to the UL (a bit more stringent), except that CSA (or
    	recognized equivalent) approval is required by law.
    	Again, like the UL, if a fire was caused by non-CSA-approved
    	equipment, your insurance company may not have to pay the
    	Note: strictly speaking, there usually is a legal way around
    	the lack of a CSA sticker.  In some cases (eg: Ontario), a
    	local hydro inspection prior to purchase, or prior to use, is
    	acceptable.  The hydro inspector will affix a "hydro sticker"
    	to the unit, which is as good as CSA approval.  But it costs
    	money - last I knew, $75 per unit inspected.
    	ULC (Underwriters Laboratory of Canada) is an independent
    	organization that, amongst other things, undertakes the
    	quarterly inspection of manufacturer's to ensure continued
    	compliance of UL Listed/Recognized products to Agency reports
    	and safety standards. This work is done under contract to UL
    	Inc (Follow-up Services Division). They are not a branch or
    	subsidiary of UL.
    Subject: What impact does NAFTA have on wiring standards and approvals?
    	The North America Free Trade Agreement came into effect on
    	January 1st, 1994.  NAFTA attempts to bring down trade barriers
    	between Mexico, Canada and the USA.  One of the "barriers" has
    	been that of approval of material.  As of January first, CSA
    	approval of a device is legally considered equivalent to UL
    	approval in the USA.  Conversely, UL is now accepted as
    	equivalent to CSA approval in Canada.  Theoretically, this
    	means that devices marked only with UL approval are acceptable
    	in the CEC, and conversely CSA approval by itself of a device
    	is accepted by the NEC.  This allows much freer trade in
    	electrical materials between the two countries.
    	This doesn't affect the electrical codes themselves, so the
    	differences in practice between the NEC and CEC will remain.
    	It is also my understanding that bilateral acceptance of
    	"approval" will only apply when the standards applied are
    	reasonably the same.  As an example, a cable approved by the
    	NEC for a given purpose may not be acceptable by the CEC for
    	the same purpose if the standards requirements are different.
    	Eg: "NMD" ("non-metallic, damp") cable is usually required for
    	residences in Canada.  "NM" cable ("non-metallic, not damp
    	locations) which is used in the same situations in the US,
    	would probably not be acceptable in Canada.  Also,
    	municipalities can add additional requirements on top of the
    	CEC, as they can in the US over the NEC.
    	Thus, Canadians will probably start seeing UL-only approved
    	materials in stores, and Americans the same regarding
    	CSA-only.  But some differences will remain.  When in doubt on
    	major items, consult an inspector.  At least in Canada, the
    	fact that the material is available in a store usually means
    	that it's okay to install.
    Subject: Are there any cheaper, easier to read books on wiring?
    	USA: The following three books were suggested by our readers
    	    Residential Wiring
    	    by Jeff Markell,
    	    Craftsman Books,
    	    Carlsbad CA for $18.25. ISBN 0-934041-19-9.
    	    Practical Electrical Wiring
    	    Residential, Farm and Industrial,  Based on the National
    	    Electrical Code    ANSI/NFPA 70
    	    Herbert P. Richter and W. Creighton Schwan
    	    McGraw-Hill Book Co.
    	    Wiring Simplified
    	    H. P. Richter and W. C. Schwan
    	    Park Publishing Co.
    	    The Electrician's Toolbox Manual
    	    Rex Miller
    	    Prentice Hall (ARCO) 1989
    	    ISBN 0-13-247701-7 $11.00 
    	Try to make sure that the book is based on the latest NEC
    	revision.  Which is currently 1993.
    	Canada: P.S. Knight authors and publishes a book called
    	"Electrical Code Simplified".  There appears to be a version
    	published specific to each province, and is very tied into the
    	appropriate provincial code.  It focuses on residential wiring,
    	and is indispensible for Canadian DIY'ers.  It is better to get
    	this book than the CEC unless you do a lot of wiring (or answer
    	questions on the net ;-).
    	It is updated each time the provincial codes are.  This book is
    	available at all DIY and hardware stores for less than C$10.
    Subject: Inspections how and what?  Why should I get my wiring inspected?
    	Most jurisdictions require that you obtain a permit and
    	inspections of any wiring that is done.  Amongst other more
    	mundane bureaucratic reasons (like insurance companies not
    	liking to have to pay claims), a permit and inspections
    	provides some assurance that you, your family, your neighbors
    	or subsequent owners of your home don't get killed or lose
    	their homes one night due to a sloppy wiring job.
    	Most jurisdictions have the power to order you to vacate your
    	home, or order you to tear out any wiring done without a
    	permit.  California, for instance, is particularly nasty about
    	If fire starts in your home, and un-inspected wiring is at
    	fault, insurance companies will often refuse to pay the damage
    	In general, the process goes like this:
    		- you apply to your local inspections office or building
    		  department for a permit.  You should have a sketch or
    		  detailed drawing of what you plan on doing.  This is
    		  a good time to ask questions on any things you're not
    		  sure of.  If you're doing major work, they may impose
    		  special conditions on you, require loading
    		  calculations and ask other questions.  At this point
    		  they will tell you which inspections you will need.
    		- If you're installing a main panel, you will need to
    		  have the panel and service connections inspected
    		  before your power utility will provide a connection.
    		  This is sometimes done by the local power authority
    		  rather than the usual inspectors.
    		- After installing the boxes and wiring, but before
    		  the insulation/walls go up, you will need a
    		  "rough-in" inspection.
    		- After the walls are up, and the wiring is complete,
    		  you will need a "final inspection".
    Subject: My house doesn't meet some of these rules and regulations.
    	Do I have to upgrade?
    	In general, there is no requirement to upgrade older dwellings,
    	though there are some exceptions (ie: smoke detectors in some
    	cases).  However, any new work must be done according to the
    	latest electrical code.  Also, if you do ``major'' work, you
    	may be required to upgrade certain existing portions or all
    	of your system.  Check with your local electrical inspector.
    Subject: A word on voltages: 110/115/117/120/125/220/240
    	One thing where things might get a bit confusing is the
    	different numbers people bandy about for the voltage of
    	a circuit.  One person might talk about 110V, another 117V
    	or another 120V.  These are all, in fact, exactly the same
    	thing...  In North America the utility companies are required
    	to supply a split-phase 240 volt (+-5%) feed to your house.
    	This works out as two 120V +- 5% legs.  Additionally, since there
    	are resistive voltage drops in the house wiring, it's not
    	unreasonable to find 120V has dropped to 110V or 240V has dropped
    	to 220V by the time the power reaches a wall outlet.  Especially
    	at the end of an extension cord or long circuit run.  For a number
    	of reasons, some historical, some simple personal orneryness,
    	different people choose call them by slightly different numbers.
    	This FAQ has chosen to be consistent with calling them "110V" and
    	"220V", except when actually saying what the measured voltage will
    	be.  Confusing?  A bit.  Just ignore it.
    	One thing that might make this a little more understandable
    	is that the nameplates on equipment ofen show the lower (ie: 110V
    	instead of 120V) value.  What this implies is that the device
    	is designed to operate properly when the voltage drops that
    	208V is *not* the same as 240V.  208V is the voltage between
    	phases of a 3-phase "Y" circuit that is 120V from neutral to any
    	hot.   480V is the voltage between phases of a 3-phase "Y"
    	circuit that's 277V from hot to neutral.
    	In keeping with 110V versus 120V strangeness, motors intended
    	to run on 480V three phase are often labelled as 440V...
    Subject: What does an electrical service look like?
    	There are logically four wires involved with supplying the
    	main panel with power.  Three of them will come from the utility
    	pole, and a fourth (bare) wire comes from elsewhere.
     	The bare wire is connected to one or more long metal bars pounded
     	into the ground, or to a wire buried in the foundation, or sometimes
     	to the water supply pipe (has to be metal, continuous to where
    	the main water pipe entering the house.  Watch out for galvanic
    	action conductivity "breaks" (often between copper and iron pipe).
    	This is the "grounding conductor".  It is there to make sure that
    	the third prong on your outlets is connected to ground.  This wire
    	normally carries no current.
    	One of the other wires will be white (or black with white or
    	yellow stripes, or sometimes simply black).  It is the neutral wire.
    	It is connected to the "centre tap" (CEC; "center tap" in the
    	NEC ;-) of the distribution transformer supplying the power.  It
    	is connected to the grounding conductor in only one place (often
    	inside the panel).  The neutral and ground should not be connected
    	anywhere else.  Otherwise, weird and/or dangerous things may happen.
    	Furthermore, there should only be one grounding system in
    	a home.  Some codes require more than one grounding electrode.
    	These will be connected together, or connected to the neutral
    	at a common point - still one grounding system.  Adding additional
    	grounding electrodes connected to other portions of the house
    	wiring is unsafe and contrary to code.
    	If you add a subpanel, the ground and neutral are usually
    	brought as separate conductors from the main panel, and are
    	not connected together in the subpanel (ie: still only one
    	neutral-ground connection).  However, in some situations 
    	(certain categories of separate buildings) you actually do
    	have to provide a second grounding electrode - consult your
    	The other two wires will usually be black, and are the "hot"
    	wires.  They are attached to the distribution transformer as
    	The two black wires are 180 degrees out of phase with each
    	other.  This means if you connect something to both hot wires,
    	the voltage will be 220 volts.  If you connect something to the
    	white and either of the two blacks you will get 110V.
    	Some panels seem to only have three wires coming into them.
    	This is either because the neutral and ground are connected
    	together at a different point (eg: the meter or pole) and one
    	wire is doing dual-duty as both neutral and ground, or in some
    	rare occasions, the service has only one hot wire (110V only
    Subject: What is a circuit?
    	Inside the panel, connections are made to the incoming wires.
    	These connections are then used to supply power to selected
    	portions of the home.  There are three different combinations:
    		1) one hot, one neutral, and ground: 110V circuit.
    		2) two hots, no neutral, and ground: 220V circuit.
    		3) two hots, neutral, and ground: 220V circuit + neutral,
    		   and/or two 110V circuits with a common neutral.
    	(1) is used for most circuits supplying receptacles and
    	lighting within your house.  (3) is usually used for supplying
    	power to major appliances such as stoves, and dryers - they
    	often have need for both 220V and 110V, or for bringing several
    	circuits from the panel box to a distribution point.  (2) is
    	usually for special 220V motor circuits, electric heaters, or
    	air conditioners.
    	[Note: In the US, the NEC frequently permits a circuit similar
    	to (2) be used for stoves and dryers - namely, that there
    	are two hot wires, and a wire that does dual duty as neutral
    	and ground, and is connected to the frame as well as providing
    	the neutral for 110V purposes - three prong plugs instead
    	of four (*only* for stoves/dryers connected to the main panel.
    	When connected to most sub-panels, 4 prong plugs and receptacles
    	are required).  In our not-so-humble opinion this is crazy, but
    	the NFPA claims that this practice was re-evaluated for the 1992 NEC,
    	and found to be safe.  Check your local codes, or inquire as to
    	local practice -- there are restrictions on when this is
    	(1) is usually wired with three conductor wire: black for hot,
    	white for neutral, and bare for grounding.
    	(2) and (3) have one hot wire coloured red, the other black, a
    	bare wire for grounding, and in (3) a white wire for neutral.
    	You will sometimes see (2) wired with just a black, white and ground
    	wire.  Since the white is "hot" in this case, both the NEC and CEC
    	requires that the white wire be "permanently marked" at the ends
    	to indicate that it is a live wire.  Usually done with paint, nail
    	polish or sometimes electrical tape.
    	Each circuit is attached to the main wires coming into the
    	panel through a circuit breaker or fuse.
    	There are, in a few locales, circuits that look like (1), (2)
    	or (3) except that they have two bare ground wires.  Some places
    	require this for hot tubs and the like (one ground is "frame ground",
    	the other attaches to the motor).  This may or may not be an
    	alternative to GFCI protection.
    Subject: "grounding" versus "grounded" versus "neutral".
    	According to the terminology in the CEC and NEC, the
    	"grounding" conductor is for the safety ground, i.e., the green
    	or bare or green with a yellow stripe wire.  The word "neutral"
    	is reserved for the white when you have a circuit with more than 
    	one "hot" wire.  Since the white wire is connected to neutral and
    	the grounding conductor inside the panel, the proper term is
    	"grounded conductor".  However, the potential confusion between
    	"grounded conductor" and "grounding conductor" can lead to
    	potentially lethal mistakes - you should never use the bare wire
    	as a "grounded conductor" or white wire as the "grounding conductor",
    	even though they are connected together in the panel.
    	[But not in subpanels - subpanels are fed neutral and ground
    	separately from the main panel.  Usually.]
    	Note: do not tape, colour or substitute other colour wires for the
    	safety grounding conductor.
    	In the trade, and in common usage, the word "neutral" is used
    	for "grounded conductor".  This FAQ uses "neutral" simply to
    	avoid potential confusion.  We recommend that you use "neutral"
    	too.  Thus the white wire is always (except in some light
    	switch applications) neutral.  Not ground.
    Subject: What does a fuse or breaker do?  What are the differences?
    	Fuses and circuit breakers are designed to interrupt the power
    	to a circuit when the current flow exceeds safe levels.  For
    	example, if your toaster shorts out, a fuse or breaker should
    	"trip", protecting the wiring in the walls from melting.  As
    	such, fuses and breakers are primarily intended to protect the
    	wiring -- UL or CSA approval supposedly indicates that the
    	equipment itself won't cause a fire.
    	Fuses contain a narrow strip of metal which is designed to melt
    	(safely) when the current exceeds the rated value, thereby
    	interrupting the power to the circuit.  Fuses trip relatively
    	fast.  Which can sometimes be a problem with motors which have
    	large startup current surges.  For motor circuits, you can use
    	a "time-delay" fuse (one brand is "fusetron") which will avoid
    	tripping on momentary overloads.  A fusetron looks like a
    	spring-loaded fuse.  A fuse can only trip once, then it must be
    	Breakers are fairly complicated mechanical devices.  They
    	usually consist of one spring loaded contact which is latched
    	into position against another contact.  When the current flow
    	through the device exceeds the rated value, a bimetallic strip
    	heats up and bends.  By bending it "trips" the latch, and the
    	spring pulls the contacts apart.  Circuit breakers behave
    	similarly to fusetrons - that is, they tend to take longer to
    	trip at moderate overloads than ordinary fuses.  With high
    	overloads, they trip quickly.  Breakers can be reset a finite
    	number of times - each time they trip, or are thrown
    	when the circuit is in use, some arcing takes place, which
    	damages the contacts.  Thus, breakers should not be used in
    	place of switches unless they are specially listed for the
    	Neither fuses nor breakers "limit" the current per se.  A dead
    	short on a circuit can cause hundreds or sometimes even
    	thousands of amperes to flow for a short period of time, which
    	can often cause severe damage.
    Subject: Breakers?  Can't I use fuses?
    	Statistics show that fuse panels have a significantly higher
    	risk of causing a fire than breaker panels.  This is usually
    	due to the fuse being loosely screwed in, or the contacts
    	corroding and heating up over time, or the wrong size fuse
    	being installed, or the proverbial "replace the fuse with a
    	penny" trick.
    	Since breakers are more permanently installed, and have better
    	connection mechanisms, the risk of fire is considerably less.
    	Fuses are prone to explode under extremely high overload.  When
    	a fuse explodes, the metallic vapor cloud becomes a conducting
    	path.  Result?  From complete meltdown of the electrical panel,
    	melted service wiring, through fires in the electrical
    	distribution transformer and having your house burn down.
    	[This author has seen it happen.]  Breakers won't do this.
    	Many jurisdictions, particularly in Canada, no longer permit
    	fuse panels in new installations.  The NEC does permit new
    	fuse panels in some rare circumstances (requiring the special
    	inserts to "key" the fuseholder to specific size fuses)
    	Some devices, notably certain large air conditioners, require fuse
    	protection in addition to the breaker at the panel.  The fuse
    	is there to protect the motor windings from overload.  Check the
    	labeling on the unit.  This is usually only on large permanently
    	installed motors.  The installation instructions will tell you
    	if you need one.
    Subject: What size wire should I use?
    	For a 20 amp circuit, use 12 gauge wire.  For a 15 amp circuit,
    	you can use 14 gauge wire (in most locales).  For a long run,
    	though, you should use the next larger size wire, to avoid
    	voltage drops.  12 gauge is only slightly more expensive than
    	14 gauge, though it's stiffer and harder to work with.
    	Here's a quick table for normal situations.  Go up a size for
    	more than 100 foot runs, when the cable is in conduit, or
    	ganged with other wires in a place where they can't dissipate
    	heat easily:
    		Gauge		Amps
    		14		15
    		12		20
    		10		30
    		8		40
    		6		65
    	We don't list bigger sizes because it starts getting very dependent
    	on the application and precise wire type.
    Subject: Where do these numbers come from?
    	There are two considerations, voltage drop and heat buildup.
    	The smaller the wire is, the higher the resistance is.  When
    	the resistance is higher, the wire heats up more, and there is
    	more voltage drop in the wiring.  The former is why you need
    	higher-temperature insulation and/or bigger wires for use in
    	conduit; the latter is why you should use larger wire for long
    	Neither effect is very significant over very short distances.
    	There are some very specific exceptions, where use of smaller
    	wire is allowed.  The obvious one is the line cord on most
    	lamps.  Don't try this unless you're certain that your use fits
    	one of those exceptions; you can never go wrong by using larger
    Subject: What does "14-2" mean?
    	This is used to describe the size and quantity of conductors
    	in a cable.  The first number specifies the gauge.  The second
    	the number of current carrying conductors in the wire - but
    	remember there's usually an extra ground wire.  "14-2" means
    	14 gauge, two insulated current carrying wires, plus bare ground.
    	-2 wire usually has a black, white and bare ground wire.  Sometimes
    	the white is red instead for 220V circuits without neutral.  In
    	the latter case, the sheath is usually red too.
    	-3 wire usually has a black, red, white and bare ground wire.
    	Usually carrying 220V with neutral.
    Subject: What is a "wirenut"/"marrette"/"marr connector"?  How are they
    	A wire nut is a cone shaped threaded plastic thingummy that's used
    	to connect wires together.  "Marrette" or "Marr connector"
    	are trade names.  You'll usually use a lot of them in DIY wiring.
    	In essence, you strip the end of the wires about an inch, twist them
    	together, then twist the wirenut on.
    	Though some wirenuts advertise that you don't need to twist the
    	wire, do it anyways - it's more mechanically and electrically
    	There are many different sizes of wire nut.  You should check
    	that the wire nut you're using is the correct size for the
    	quantity and sizes of wire you're connecting together.
    	Don't just gimble the wires together with a pair of pliers or
    	your fingers.  Use a pair of blunt nose ("linesman") pliers,
    	and carefully twist the wires tightly and neatly.  Sometimes
    	it's a good idea to trim the resulting end to make sure it
    	goes in the wirenut properly.
    	Some people wrap the "open" end of the wirenut with electrical
    	tape.  This is probably not a good idea - the inspector may
    	tear it off during an inspection.  It's usually done because
    	a bit of bare wire is exposed outside the wire nut - instead
    	of taping it, the connection should be redone.
    Subject: What is a GFI/GFCI?
    	A GFCI is a ``ground-fault circuit interrupter''.  It measures
    	the current current flowing through the hot wire and the
    	neutral wire.  If they differ by more than a few milliamps, the
    	presumption is that current is leaking to ground via some other
    	path.  This may be because of a short circuit to the chassis of
    	an appliance, or to the ground lead, or through a person.  Any
    	of these situations is hazardous, so the GFCI trips, breaking
    	the circuit.
    	GFCIs do not protect against all kinds of electric shocks.  If,
    	for example, you simultaneously touched the hot and neutral
    	leads of a circuit, and no part of you was grounded, a GFCI
    	wouldn't help.  All of the current that passed from the hot
    	lead into you would return via the neutral lead, keeping the
    	GFCI happy.
    	The two pairs of connections on a GFCI outlet are not symmetric.
    	One is labeled LOAD; the other, LINE.  The incoming power feed
    	*must* be connected to the LINE side, or the outlet will not be
    	protected.  The LOAD side can be used to protect all devices
    	downstream from it.  Thus, a whole string of outlets can be
    	covered by a single GFCI outlet.
    Subject: Where should GFCIs be used?
    	The NEC mandates GFCIs for 110V, 15A or 20A single phase
    	outlets, in bathrooms, kitchens within 6' of the sink, wet-bar
    	sinks, roof outlets, garages, unfinished basements or crawl spaces,
    	outdoors, near a pool, or just about anywhere else where you're likely
    	to encounter water or dampness.  There are exceptions for inaccessible
    	outlets, those dedicated to appliances ``occupying fixed space'',
    	typically refrigerators and freezers, and for sump pumps and
    	laundry appliances.
    	The NEC now requires that if your replace an outlet in a
    	location now requiring GFCI, you must install GFCI protection.
    	Note in particular - kitchen and bathroom outlets.
    	When using the "fixed appliance" rule for avoiding GFCI outlets,
    	single outlet receptacles must be used for single appliances,
    	duplex receptacles may be used for two appliances.
    	The CEC does not mandate as many GFCIs.  In particular, there
    	is no requirement to protect kitchen outlets, or most garage or
    	basement outlets.  Basement outlets must be protected if you
    	have a dirt floor, garage outlets if they're near the door to
    	outside.  Bathrooms and most exterior outlets must have GFCIs,
    	as do pools systems and jacuzzi or whirlpool pumps.
    	There are many rules about GFCIs with pools and so on.  This
    	is outside of our expertise, so we're not covering it in
    	detail.  See your inspector.
    	When replacing an outlet, it must now be GFCI-protected if
    	such would now be required for a new installation.  That is,
    	a kitchen outlet installed per the 1984 code need not have
    	been protected, but if that outlet is ever replaced, GFCI
    	protection must now be added (under NEC).  This is explicit
    	in the 1993 NEC, and inspector-imposed in Canada.
    	Even if you are not required to have GFCI protection, you may
    	want to consider installing it anyway.  Unless you need a GFCI
    	breaker (see below), the cost is low.  In the U.S., GFCI
    	outlets can cost as little as US$8.  (Costs are a bit higher in
    	Canada:  C$12.)  Evaluate your own risk factors.  Does your
    	finished basement ever get wet?  Do you have small children?
    	Do you use your garage outlets to power outdoor tools?  Does
    	water or melted snow ever puddle inside your garage?
    Subject: Where shouldn't I use a GFCI?
    	GFCIs are generally not used on circuits that (a) don't pose a
    	safety risk, and (b) are used to power equipment that must run
    	unattended for long periods of time.  Refrigerators, freezers,
    	and sump pumps are good examples.  The rationale is that GFCIs
    	are sometimes prone to nuisance trips.  Some people claim that
    	the inductive delay in motor windings can cause a momentary
    	current imbalance, tripping the GFCI.  Note, though, that most
    	GFCI trips are real; if you're getting a lot of trips for no
    	apparent reason, you'd be well-advised to check your wiring
    	before deciding that the GFCI is broken or useless.
    Subject: What is the difference between a GFCI outlet and a GFCI breaker?
    	For most situations, you can use either a GFCI outlet as the
    	first device on the circuit, or you can install a breaker with
    	a built-in GFCI.  The former is generally preferred, since GFCI
    	breakers are quite expensive.  For example, an ordinary GE
    	breaker costs ~US$5; the GFCI model costs ~US$35.  There is one
    	major exception:  if you need to protect a ``multi-wire branch
    	circuit'' (two or more circuits sharing a common neutral wire),
    	such as a Canadian-style kitchen circuit, you'll need a
    	multi-pole GFCI breaker.  Unfortunately, these are expensive;
    	the cost can range into the hundreds of dollars, depending on
    	what brand of panel box you have.  But if you must protect such
    	a circuit (say, for a pool heater), you have no choice.
    	One more caveat -- GFCI outlets are bulky.  You may want to use
    	an oversize box when installing them.  On second thought, use
    	large (actually deep) boxes everywhere.  You'll thank yourself
    	for it.
    	Incidentally, if you're installing a GFCI to ensure that one
    	specific outlet is protected (such as a bathroom), you don't
    	really have to go to all of the trouble to find the first
    	outlet in the circuit, you could simply find the first outlet
    	in the bathroom, and not GFCI anything upstream of it.  But
    	protecting the whole circuit is preferred.
    	When you install a GFCI, it's a good idea to use the little
    	"ground fault protected" stickers that come with it and mark
    	the outlets downstream of the GFCI.  You can figure out which
    	outlets are "downstream", simply by tripping the GFCI with the
    	test button and see which outlets are dead.
    	Note that the labels are mandatory for GFCI-protected-but-ungrounded
    	three prong outlets according to the NEC.
    Subject: What's the purpose of the ground prong on an outlet, then?
    	Apart from their use in electronics, which we won't comment on,
    	and for certain fluorescent lights (they won't turn on without
    	a good ground connection), they're intended to guard against
    	insulation failures within the device.  Generally, the case of
    	the appliance is connected to the ground lead.  If there's an
    	insulation failure that shorts the hot lead to the case, the
    	ground lead conducts the electricity away safely (and possibly
    	trips the circuit breaker in the process).  If the case is not
    	grounded and such a short occurs, the case is live -- and if
    	you touch it while you're grounded, you'll get zapped.  Of
    	course, if the circuit is GFCI-protected, it will be a very
    	tiny zap -- which is why you can use GFCIs to replace
    	ungrounded outlets (both NEC and CEC).
    	There are some appliances that should *never* be grounded.  In
    	particular, that applies to toasters and anything else with
    	exposed conductors.  Consider:  if you touch the heating
    	electrode in a toaster, and you're not grounded, nothing will
    	happen.  If you're slightly grounded, you'll get a small shock;
    	the resistance will be too high.  But if the case were
    	grounded, and you were holding it, you'd be the perfect path to
    Subject: Grounding electrode system
    |	Note that full coverage of how to install a grounding electrode
    |	system is well beyond the scope of this FAQ.  The comments made
    |	here are primarily so that the reader understands what it is
    |	for, and some of its characteristics.
    |	The grounding electrode system is a method by which the neutral
    |	and grounding conductors are connected to the common "earth"
    |	reference.  The connection from the electrical system to the
    |	grounding system is made in only one place to avoid ground
    |	loops.
    |	The grounding electrode system is _not_ intended to carry much
    |	current.  Ground faults (Ie: hot to grounded case short) are
    |	conducted down the ground wire to where it is interconnected
    |	with the neutral and hopefully the breaker/fuse trips.  The
    |	grounding electrode does not participate in such a situation.
    |	While the conductors involved in this are relatively large, they're
    |	sized for lightning strikes and other extremely short duration
    |	events.  The grounding electrode system is specifically _not_
    |	expected to have enough conductivity to trip a 15A breaker.
    |	The grounding electrode often has a moderately high
    |	resistance.  For example, according to the NEC, an acceptable
    |	ground electrode system may have 25 ohms of resistance - only
    |	5A at 120V, not enough to trip a 15A breaker.
    |	A grounding electrode system usually consists of a primary
    |	grounding electrode, plus possibly a secondary electrode.  A
    |	primary electrode can be (if in direct contact with the earth):
    |	10' of ground rod.  10' of well casing or metallic water pipe
    |	(must be connected within 5' of pipe entrance to house).  20'
    |	of copper wire buried in the bottom of the footings.  A
    |	secondary electrode will be required if the primary is a water
    |	pipe or (NEC) if the primary electrode is >25 ohms to the
    |	dirt.
    Subject: Bonding requirements
    |	All "metallic systems" in a home that are capable of being
    |	energized are required to be bonded to the grounding system.
    |	This is usually taken to mean:  metallic water supply, metallic
    |	drain-waste-vent pipe, metal ducting, gas lines, and sometimes
    |	metallic structural elements (eg: metal framing systems).
    |	The rationale for this is simple: if somehow a hot conductor contacts
    |	a water pipe, say, you don't want every plumbing fixture in your
    |	home to become live.  The bonding attempts to ensure that you have
    |	a low resistance path to the ground system at the panel, and thence
    |	to the neutral - ensuring that this ground fault is stopped by
    |	a breaker or fuse tripping.  Remember that this is independent of
    |	the grounding electrode system's conductivity.
    |	Normally the bonding of most of these systems are done by the
    |	equipment involved.  Furnace ducting is grounded by the furnace
    |	connection.  Gas line grounding is done by the gas man ;-)
    |	So we'll mainly talk about water line grounding here.
    |	The NEC appears to insist that each electrically isolated section
    |	of metallic water pipe must be jumpered together.  Take particular
    |	note that you are required to provide a jumper wire that bypasses the
    |	main water meter (especially if you're using the water supply line
    |	as a grounding electrode), and a jumper between hot and cold if the
    |	water heater is an electrical insulator.  The CEC, for example,
    |	also requires that the frame of your clothes washer is bonded to the
    |	cold water supply pipe.
    |	Exact details of how this bonding should be done is beyond the scope of
    |	this FAQ.  It tends to be a 6ga wire running from the grounding terminal
    |	of the panel to a convenient copper pipe.  If the water supply is used
    |	as a grounding electrode, the rules become stricter (5' rule applies
    |	in NEC etc.)
    Subject: Testing grounding conductors and grounding electrodes.
    |	Testing grounds is a tricky and somewhat dangerous process.
    |	Testing for continuity is not enough.  Nor is simple resistance
    |	testing.  We will outline some possible approaches, but if
    |	you're the slightest bit uncomfortable, don't even think of
    |	trying these procedures.
    |	For a ground conductor to be good, the resistance must be
    |	"low".  It must also be robust enough to withstand an overload
    |	long enough to allow the fuse or breaker to trip.  The
    |	electrical code states, as a general principle, that the
    |	resistance of the grounding conductor be such that 4-5 times
    |	the current of the breaker rating will flow.  For example, if
    |	your breaker is 15A, the grounding conductor's resistance
    |	should be low enough to permit 60-75A to flow - around 2 ohms
    |	maximum at 120V.  For comparative purposes, 1000' of 14ga wire
    |	is 1 ohm.
    |	The difficulty in older homes is that the grounding conductor's
    |	condition may be that even though the resistance is < 2 ohms, a
    |	ground connection may blow out before the fuse/breaker goes,
    |	leaving the case of the appliance that just shorted out live.
    |	Therefore, you have to measure both the resistance and it's
    |	ability to stand up to load.
    |	One simple way to perform a "real" test is dead short the hot
    |	to ground and see if the fuse or breaker trips.  This is,
    |	unfortunately, _extremely_ dangerous.  The fuse might explode.
    |	The breaker may malfunction.  You may get sprayed with molten
    |	copper.  You may start a fire.  You may get electrocuted or
    |	blinded.  So don't even think of trying this.
    |	One moderately safe approach is to connect a 100W lightbulb
    |	between hot and the ground you wish to test.  The lamp should
    |	light fully.  If you have a voltmeter, test the voltage between
    |	the ground and the neutral.  You should see less than 2 volts.
    |	If the voltage is much higher, or the lamp dims, disconnect it
    |	quickly - the ground may be overheating somewhere.  The ground
    |	should be checked for poor connections.
    |	Testing a grounding electrode is a somewhat different matter.
    |	The codes aim for a dirt-to-electrode resistance of 25 ohms or
    |	better.  One moderately safe way is:
    |		- turn off the main panel
    |		- turn off all of the breakers
    |		- disconnect the grounding electrode from the rest of
    |		  the system.  (often just a bolt in the panel)
    |		- connect a 5A fuse between the output of one 15A breaker
    |		  and the grounding electrode.  (use a 5A automotive fuse
    |		  in a pigtail holder)
    |		- turn on the main breaker and the single breaker connected
    |		  to the 5A fuse.
    |		- if the 5A fuse blows, your ground is good.
    Subject: Why is one prong wider than the other?  Polarization
    	Nowadays, many two-prong devices have one prong wider than the
    	other.  This is so that the device could rely (not guaranteed!)
    	on one specific wire being neutral, and the other hot.
    	This is particularly advantageous in light fixtures, where the
    	the shell should neutral (safety), or other devices which want to
    	have an approximate ground reference (ie: some radios).
    	Most 2-prong extension cords have wide prongs too.
    	This requires that you wire your outlets and plugs the right
    	way around.  You want the wide prong to be neutral, and the
    	narrow one hot.  Most outlets have a darker metal for the
    	hot screw, and lighter coloured screw for the neutral.
    	If not, you can usually figure out which is which by which
    	prong the terminating screw connects to.
    Subject: How do I convert two prong receptacles to three prong?
    	Older homes frequently have two-prong receptacles instead
    	of the more modern three.  These receptacles have no safety
    	ground, and the cabling usually has no ground wire.  Neither
    	the NEC or CEC permits installing new 2 prong receptacles anymore.
    	There are several different approaches to solving this:
    	    1) If the wiring is done through conduit or BX, and the
    	       conduit is continuous back to the panel, you can connect
    	       the third prong of a new receptacle to the receptacle
    	       box.  NEC mainly - CEC frowns on this practice.
    	    2) If there is a metallic cold water pipe going nearby, and
    |	       it's electrically continuous to the main house ground
    |	       point, you can run a conductor to it from the third
    |	       prong.  You MUST NOT assume that the pipe is continuous,
    |	       unless you can visually check the entire length and/or
    |	       test it.  Testing grounds is tricky - see "Testing
    |	       Grounds" section.
    	    3) Run a ground conductor back to the main panel.
    	    4) Easiest: install a GFCI receptacle.  The ground lug
    	       should not be connected to anything, but the GFCI
    	       protection itself will serve instead.  The GFCI
    	       will also protect downstream (possibly also two prong
    	       outlets).  If you do this to protect downstream outlets,
    	       the grounds must not be connected together.  Since it
    	       wouldn't be connected to a real ground, a wiring fault
    	       could energize the cases of 3 prong devices connected
    	       to other outlets.  Be sure, though, that there aren't
    	       indirect ground plug connections, such as via the sheath
    	       on BX cable.
    	The CEC permits you to replace a two prong receptacle with a three
    	prong if you fill the U ground with a non-conducting goop.
    	Like caulking compound.  This is not permitted in the NEC.
    	The NEC requires that three prong receptacles without ground
    	that are protected by GFCI must be labelled as such.
    	See the next section about computers on GFCI-protected groundless
    Subject: Surges, spikes, zaps, grounding and your electronics
    	Theoretically, the power coming into your house is a perfect AC
    	sine wave.  It is usually quite close.  But occasionally, it
    	won't be.  Lightning strikes and other events will affect the
    	power.  These usually fall into two general categories: very
    	high voltage spikes (often into 1000s of volts, but usually
    	only a few microseconds in length) or surges (longer duration,
    	but usually much lower voltage).
    	Most of your electrical equipment, motors, transformer-operated
    	electronics, lights, etc., won't even notice these one-shot
    	events.  However, certain types of solid-state electronics,
    	particularly computers with switching power supplies and MOS
    	semiconductors, can be damaged by these occurances.  For
    	example, a spike can "punch a hole" through an insulating layer
    	in a MOS device (such as that several hundred dollar 386 CPU),
    	thereby destroying it.
    	The traditional approach to protecting your electronics is to
    	use "surge suppressors" or "line filters".  These are usually
    	devices that you plug in between the outlet and your
    	Roughly speaking, surge suppressors work by detecting
    	overvoltages, and shorting them out.  Think of them as voltage
    	limiters.  Line filters usually use frequency-dependent
    	circuits (inductors, capacitors etc.) to "tune out" undesirable
    	spikes - preventing them from reaching your electronics.
    	So, you should consider using suppressors or filters on your
    	sensitive equipment.
    	These devices come in a very wide price range.  From a couple
    	of dollars to several hundred.  We believe that you can protect
    	your equipment from the vast majority of power problems by
    	selecting devices in the $20-50 range.
    	A word about grounding: most suppressors and EFI filters
    	require real grounds.  Any that don't are next to useless.
    	For example, most surge suppressors use MOVs (metal oxide
    	varistors) to "clamp" overvoltages.  Yes, you can have a
    	suppressor that only has a MOV between neutral and hot to
    	combat differential-mode voltage excursions, but that isn't
    	enough.  You need common-mode protection too.  Good suppressors
    	should have 3 MOVs, one between each pair of wires.  Which
    	means you should have a good solid ground.  Eg: a solidly
    	connected 14ga wire back to the panel.  Not rusty BX armour or
    	galvanized pipe with condensation turning the copper connection
    	Without a ground, a surge or spike is free to "lift" your
    	entire electronics system well away from ground.  Which is
    	ideal for blowing out interface electronics for printer ports
    	Secondly, static electricity is one of the major enemies of
    	electronics.  Having good frame grounds is one way of
    	protecting against static zaps.
    	If you're in the situation of wanting to install computer
    	equipment on two wire groundless circuits take note:
    	Adding a GFCI outlet to the circuit makes the circuit safe for
    	you.  But it doesn't make it safe for your equipment - you need
    	a ground to make surge suppressors or line filters effective.
    Subject: Are you sure about GFCIs and ungrounded outlets?
    	Should the test button work?
    	The NEC, section 210-7(d), and CEC, section 26-700(9), are quite
    	explicit that GFCIs are a legal substitute for a grounded outlet
    	in an existing installation where there is no ground available in
    	the outlet box.
    	But your local codes may vary.  As for the TEST button -- there's
    	a resistor connecting the LOAD side of the hot wire to the LINE
    	side of the neutral wire when you press the TEST button.  Current
    	through this resistor shows up as an imbalance, and trips the GFCI.
    	This is a simple, passive, and reliable test, and doesn't require
    	a real ground to work.  If your GFCI does not trip when you press
    	the TEST button, it is very probably defective or miswired.  Again:
    	if the test button doesn't work, something's broken, and potentially
    	dangerous.  The problem should be corrected immediately.
    	The instructions that come with some GFCIs specify that the ground
    	wire must be connected.  We do not know why they say this.  The
    	causes may be as mundane as an old instruction sheet, or with the
    	formalities of UL or CSA listing -- perhaps the device was never
    	tested without the ground wire being connected.  On the other hand,
    	UL or CSA approval should only have been granted if the device
    	behaves properly in *all* listed applications, including ungrounded
    	outlet replacement.  (One of us called Leviton; their GFCIs are
    	labeled for installation on grounded circuits only.  The technician
    	was surprised to see that; he agreed that the NEC does not require
    	it, and promised to investigate.)
    Chris Lewis: _Una confibula non sat est_
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