A very important consideration about US electical code is that you are
supposed to derate circuits 20%. So a 20 amp breaker which is rated at
2400 watts is actually sized at 16 amps or 1920 watts. Although running
it at 20 amps will not burn the house down, the codes require the
derating. I work in the home automation industry and deal with
electricians daily. If they go over a few watts here and there they
don't worry. I believe the code does allow for 20 amps on circuits if
the 20 amp load doesn't exceed 3 hours. It's all about the heat rise and
cable lengths.  Remember that when calculating cable lengths for voltage
drop you have to double the distance.  An actual hundred foot run to an
outlet is factored at 200 feet.


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Matt Redmond
Sent: Tuesday, August 17, 2004 7:00 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [OT:] Inside wiring - what gauge?


To those smarter & more resourceful than I,

I'm in the middle of wiring & sheet-rocking my detached garage.  It is a
two-car, about 22'^2.  I've run 12 gauge cable from my fuse box (in the
front corner of the garage) to each of various collections of outlets
spaced therein.

My question is:  How long a run of 12 gauge solid copper cable will
handle at 20A @ 120V?  Will my 12 gauge cable carry 20A to any spot in
the garage - or do I need to put 15A breakers in?

Thanks!

-matt redmond

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