22 conductors in what size and type of pipe?
What is the ambient temperature?
Is the pipe pretty uniformly hot or is there a hot spot?
> none are overloaded,
Assuming that the circuit breakers are in working order, that probably has to be true based on the #12 takes 20 A generality.
But you have a problem. You've got over 9 conductors in one conduit and you did not derate. So just maybe they are way overloaded.
>I vaguely remember that nonlinear loads can mess up some types of loads,
On the branch side, that is a problem only when the neutrals are shared on a multiwire. In that case, the neutrals can be overloaded which means that you need to derate them even further.
Do you have 22 conductors for the eleven circuits or perhaps only 17?
To me it sounds like you need more conduits, heavier wire, and perhaps a neutral per circuit or oversized neutrals.
[This message has been edited by Dspark (edited 07-20-2001).]