Re: Electricians - Have an electrical question
- From: "Proctologically Violated©®" <physical@xxxxxxxxx>
- Date: Thu, 2 Feb 2006 15:24:50 -0500
Current ratings for wire is sort of voodoo-ish.
The current rating is not just based on copper gauge, but the type of
insulation AND the type of raceway (conduit) used AND the number of other
wires in sed raceway, as well as ambient temperature and permissible rise in
IOW, the concern is for *heat*. The new insulations that can tolerate more
heat bump up the current rating of the same copper gauge!
Imo, these ratings are conservative. The base rating is given in the NEC
(National Electric Code), w/ each municipality giving it their own spin.
NYC was ridiculously strict, at one time, and then lightened up a little.
For example, #8 THHN stranded wire, can *easily* handle 60-80 continuous
amps over a 50 ft run--gets slightly warm. But it is "rated" at about 45.
In the very old days, the wires from the pole to the house were run *bare*,
for maximum current-carrying capacity. Tough on the squirrels, tho.
OTOH, doesn't hurt to have extra capacity, esp. for things like electric
heaters, lighting, the occasional microwave, fridge, etc. Thus, the
"incidental load" can be pretty substantial, depending depending.
On a cold day, my shop can be drawing 30 A (at 120V) before I've turned on a
And, if I'm going to be using the welder at full tilt, occasionally I'll
turn a few things off, or make sure the dishwasher/dryer/etc. are off in the
Apropos of the above, the rating varies from 70 A to 278 A!! 1996 NEC.
Now, the 278 amp rating was for *nickel* covered wire (apropos of the thread
Surprises about electrical conductivity--nickel apparently is Da Bomb,
rating-wise!), but even w/o nickel, #4 wire can be rated up to 220!
Typically, tho, the rating for #4 hovers around 100, up to about 140-160.
Most local codes, and the NEC, for, say, two #4/one #8-10 (neutral)/one #12
(grnd) in a 1" pipe would be 80-100 amps.
Which, again, is very conservative, imo.
But, running larger wire--even considerably larger--is a cheap way to
prepare for the future.
You may even want to run an extra wire in the conduit for a third phase,
depending on where you might place a rotary phase converter.
formerly Droll Troll
"sparty" <longoja@xxxxxxxxx> wrote in message
100A seems high for 4/3 NM-B, but the Electrician said that was fine?
Where did you get it from?
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