You don't have to use the 60C column if the terminals are explicity rated at 75C, and most are now days. So you can have an 85A circuit with a 90A breaker if necessary. But there are many issues here we can't answer:Originally posted by rsmith46
This is wrong, the 90*c column you looked that up in is to be used for deration corrections only. You can't go over the termination rating, which would be 75*c. But under 100 amps you have to use the 60*c column which is 70amps for #4 copper. That #4 from the main panel can only be protected by a 70amp breaker, and that's before you allow for voltage drop.
Is this a branch circuit that has been tapped 60A and 30A? Or is it a feeder with feeder taps or a subpanel? What size breaker was used at the source of the #4 wire and was it sized for 125% of the heater load + the 125% of the fan load?
If there is a junction box where the #4 has been tapped into two smaller wires (such as a #6 and a #10), I don't believe this is legal as you can't tap a branch circuit (only a feeder). But doing this tap inside the air handler right at the breaker may be legal if the instructions say you can do that.
Many air handlers come with two ways of connecting them -- a lug for a huge circuit that is split inside the air handler to different heating elements or stages (usually a big lug bar that mounts into both breakers like a wire), or two separate branch circuits that terminate onto two breakers or switches in the airhandler one for each heating element or stage. If the instructions allow both methods, then this may be OK. Some others are quite picky and demand one way or the other. The key here is how the manufacturer listed the electrical section of the equipment, and you can only connect it via the way(s) it was listed.