On Tue, 04 Sep 2007 21:34:16 -0600, Joe Pfeiffer
wrote:

Ned Simmons writes:

Seems like a perfectly good analogy to me. The cord is sized
considering the nature of the load, not the capacity of the circuit
that's feeding it. The welder in question draws about 30A @ 30% duty
cycle.

You're assuming the conditions of setting the duty cycle of the welder
also apply to the duty cycle of the cord. I don't see *any* reason to
believe that's going to be the case. When I see a duty cycle rating
for an extension cord, I'll believe that it applies to it. In the
mean time, I'll use a cord rated for the peak load that it will be
called on to handle.

I'm not assuming anything. See the NEC article on welders, which
recognizes the intermittent nature of welding and allows for
conductors with an ampacity lower than the breaker's setting on welder
circuits.

There's a similar situation for motor branch circuits that accomodates
the starting current of induction motors.

--
Ned Simmons