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Re: lights and electrical

To: Mike Rambour <mikey@b2systems.com>
Subject: Re: lights and electrical
From: Douglas Shook <shook@usc.edu>
Date: Tue, 11 Jul 2000 20:30:46 -0700
Mike Rambour wrote:
> 
>    I have a "expanded" garage that was expanded by punching out the back
> wall into the backyard another 16 feet, the end result is my garage is
> 24ft. wide by 38 ft. deep.  I wired this up with lots of lights and I mean
> lots.  I have a total of 14 4ft. 40watt fluorescent bulbs and 4 8ft. ?watt
> bulbs.  Thats a lot of lights most are 2 bulb fixtures placed right over a
> tool, the 4bulb fixture is over the workbench. 

Hi Mike,

You can do a rough calculation of your lighting load by simply
multiplying the wattage of the bulb by how many you have of each
type, and then divide by 120.  Four foot bulbs generally are 40
watt (though some now are less), and the eight foot bulbs
generally are 60 watt.

A 40 watt bulb draws 40/120=.33 amp
A 60 watt bulb draws 60/120=.5  amp 

With florescent bulbs, the ballast also draws current and could
add 20% more than the rated wattage.

However, the most important aspect here is the wiring gauge
versus the breakers you are using.  You should have 14# wire for
a 15 amp breaker, 12# wire for a 20 amp breaker and 10# wire for
a 30 amp breaker.  If you use a larger breaker for a smaller
gauge wire, you are risking overheating and a fire hazard.

Please make sure you have at least 12# wire on that 20 amp
breaker and 10# wire on that 25 amp load (I think it was your
radial arm saw).

Of course when you use 220VAC, you cut your current draw in half
for the same power (use 220VAC motors whenever you have the
option).

If you are in doubt, use smaller breakers to avoid overheating
and risk of fire. If you start popping breakers, then you know
what your total load is exceeding. It may be worth the $3 it
costs for the "test" breaker.
 
regards,

doug shook

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