On Mar 12, 10:50 am, "Don Phillipson"
wrote:
"Mike Hartigan" wrote in message

.net...

Without consulting the code, it seems that everyone "just knows" that
14 gauge is used for 15 amps, 12 for 20 amps, etc. My question is -
how much margin of safety is there in this? I'm assuming that the
temperature of the wire at load was used to actually establish the
code.

Why not ask whatever agency prepares the NEC?

I suspect that all you'd get from them would be a form letter
explaining that you should never stray outside the code. And
justifiably, since 'officially' specifying how much headroom there is
in these requirements could be (and likely would be) interpreted as
tacit approval for exceeding them. Kind of like a posted speed limit
- if a cop tells you verbally that they won't write you a ticket for
exceeding the limit by less than 5 mph, that's one thing. If, on the
other hand, he gives you a piece of paper or an email saying this,
then the speed limit 'officially' becomes 5 mph above the posted limit.