ECN Forum Forums General Topics of the Trade General Discussion Area A-B ser. 193 Overloads

Don't mean to hog this thread, (not talking to myself!!), but even the A-B OL's that are rated up to 45A have 12AWG.

So, apparently 12AWG can safely carry 45A?

Seems like the 12AWG would get hot, resulting in tripping the overload, but maybe that's how they are designed to work, as John Stienke has stated.

Seems wierd to me, what about the code article about industrial machinery (Art. 670 2002NEC), or NFPA 79 dealing with industrial machinery?

Yes many of us have posted to the wrong thread at least once, nothing to worry about.

I do not mean to sound harsh but you really just have to forget about 310.16 relating to the wire on these OLs.

310.16 has nothing to do with what manufacturers do. That is not bad, the manufacturers equipment is tested by UL or some other organization to make sure it will work without a danger.

Again forget about the NEC relating to what the manufacturers do. It does not apply to them and would really mess things up if it did.

That said 310.16s ratings are based on Insulated Conductors Rated 60°C Through 90°C Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F)

The fact the conductors are insulated makes a huge difference. The fact they may be bundled in a cable makes a difference.

On the other hand a bare 12 AWG copper in 'free air' can handle, without melting out, much more than 45 amps.

310.16 ratings are based on keeping the conductor cool enough not to damage the insulation.

Back to the OLs, in order for the OLs to do the job they are supposed to, they must get hot. Many people refer to OLs as overload heaters for this very reason.

By selecting the correct 'heater' the bi metal strips in the OL contact block will be heated to the point the contacts open if the motor starts drawing more amps then the heater is designed to allow.

Bob

For what it is worth, I have read that 14 AWG copper will melt out at about 200 amps.

Of course long before the copper melts out the insulation would be smoke and ash.

Bob

[This message has been edited by iwire (edited 11-30-2004).]