Be VERY careful following this advice.
Ground and neutral _are_ tied together at the service entrance, but
should never be tied together anywhere else. Neutral is a current
carrying conductor and can be several volts above safety ground. The
safety ground should never be a current carrying conductor -- it is
there to provide a safe return for any leakage, preventing that
leakage from going through a human being.
I don't know about five phases per generator -- I've only seen three
and six. All three phases coming into your panel should be
well-regulated; if they are not, take it up with the power company.
They will be very interested, as they work very hard to keep all three
phases balanced.
The system Rod describes "110/110/200" (each measured to ground) is
known as a delta configuration. The "110" (actually 120) volt legs
are available for lighting, office equipment and other single-phase
devices. The third leg is actually a nominal 208 volts
(120*sqrt(3.0)) to ground. Some installations use this voltage
exclusively for lighting, allowing the 120 to be used for all other
office-like equipment. The motors and other three-phase equipment
will see 240 volts/3 phase. (The nomenclature 110 is really false;
the voltage can vary from 110 to 120 and is usually held to 115 to
117.) From each leg to each other (A-B, A-C, B-C) you will always
measure the nominal 240 volts, which is what makes is 240 volt/3
phase. (No it's not 440 (or 480;) you'll never be able to get 440 out
of a 220 system without adding a transformer.
If you don't understand this much, get a real electrician to install
your equipment; rubber shoes won't be enough. Look in the yellow
pages and "building" be damned. Management says move Monday, you can
move Monday, but without an electrician, you don't have any equipment
to work with. If you do it yourself and fry the equipment, you still
don't have any equipment to work with.
The receptacle you describe does not have provisions for a neutral;
all I see are three phases and a safety ground. Without a dedicated
neutral conductor, you are SOL.
HTH,
Donald.
> From: "Ron Schmittou" <rs1121@earthlink.net>
> Date: Thu, 2 Oct 2003 10:16:25 -0500
>
>
> Your right about the three hot legs and one ground. Each of the hot legs is
> a different phase (power generation companies produce 5 phases per
> generator) Normally I have always called this a 440 circuit - no matter
> which two hot legs you tap will give you 220v - so you have two 220v taps =
> 440v. The third phase is usually marked coming into your panel, and in my
> experience you don't want to use this one - most electricians call it the
> wild leg because it is generally not as regulated as the first two are, if
> you measure the lines coming in to the box you will usually see the
> following:
>
> Phase 1 - 110 to ground
> Phase 2 - 110 to Ground
> Phase 3 - 200 - 250 to ground
>
> The trick will be to identify which phase is which line on your outlet.
> Once you have done that you can make a special cord / outlet box that has
> one line to the phase 1 and both the neutral and ground wire going to the
> ground side of the original outlet. Most people cringe at wiring the
> neutral and ground together, but electrically it makes no difference - they
> are always wired together in the breaker panel anyway (unless you are
> running an isolated ground setup)
>
> Good luck and wear rubber shoes!
>
>
> Ron Schmittou
> APEX Computer Service
> (325) 690-9509 Direct - Forwards to Cell/Voice Mail
> (325) 690-9514 Direct Fax
> (325) 676-9507 Main Line
> (325) 676-9510 Main Fax
>
>
> -----Original Message-----
> From: shop-talk-owner@autox.team.net
> [mailto:shop-talk-owner@autox.team.net]On Behalf Of Brian Kemp
> Sent: Wednesday, October 01, 2003 6:25 PM
> To: shop-talk@autox.team.net
> Subject: 120V from 250V 3 phase?
>
>
>
> I have a power problem in the office I'm going to be moving into
> shortly. I have a rack of computer equipment that needs a dedicated 120V
> 20A circuit that doesn't exist in the new location. What I do have is a
> twist lock 250V 20A 3 phase outlet 4 wire outlet. According to
> http://www.diallighting.com/spec0027.htm, it is a NEMA L15-20 outlet.
>
> I'd like to make a cord to plug into this outlet and get a standard 120V
> receptacle that I can plug the computer rack into. I expect that this is
> possible, but hope someone out there can confirm that it is safe for the
> equipment.
>
> I'd try and use an electrician to put on the proper outlet, but the
> building is less than helpful and it will take more than a month to
> coordinate funding transfers, insurance requirements, and approval.
> Management told me I'm moving Monday.
>
> The outlet has 4 slots:
> 1. prong like a bent "L"
> 2. narrow slot
> 3 and 4. wider slots
>
> Thinking a 3 phase system needs 3 "hot" lines leads me to believe I
> either have a neutral or ground as the 4th wire. While I know neutral
> and ground are probably connected at the breaker box, I'm not going to
> chance a bunch of expensive computer equipment on a poor power supply.
> So as it is now, I don't think this will work.
>
> I've done enough electrical work to understand what I'm doing, but would
> like confirmation from one of the smarter people about this idea. I
> looked for a UPS to go into the outlet, but didn't find any with a 3
> phase input.
>
> Thanks,
>
> Brian Kemp
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