Looking for validation or correction on my understanding of requirements for wiring 5 ton Trane air handler with 20kw heat strips. Of course, I read the label and identified that there are (2) 240v circuits required. Minimum circuit ampacities are 57 and 50 amps respectively. MOPs are accordingly 60 and 50. The heat strips are designated 40a per circuit. It's indoors in basement and wire runs from panel are about 25 feet.
The heating system was recently installed and HVAC contractor reused existing 2/0 AL cable connected in my panel to a single 4 pole 125a breaker. He installed a single feed kit that serves the (2) 60a disconnects in the unit. Concerns: 1) the single feed kit is labeled for use only up to 100a, 2) the air handler is labeled for use only with copper wire.
I therefore would like to have new wiring run to the heater. My options, as I understand them, are a) keep the single feed kit and run a single copper feed from the panel presumably with a 100a breaker replacing the 125a or b) remove the single feed kit and run two feeds, one for each of the circuits in the air handler, appropriately sized and connected to one 50a and one 60a breaker.
Is there a general preference of rule of thumb for which of these options is best? Will the single feed with 100a breaker be adequate or will it trip when running on full aux heat?
Using sizing calculators, tables and derating - appears that single 100a feed will require either 1 awg copper NM (SE) or 3 awg THHN in conduit. The air handler uses 2 conductors plus ground (no neutral) for each circuit and I have not seen or been able to find 2-conductor copper plus ground in 1 AWG or larger.
Separate feeds will require either 4 awg 2-conductor copper plus ground NM (also difficult to find) or 4 awg THHN in conduit (which would require 4 THHN conductors plus ground in a conduit - for which I derated the ampacity of the cable to 80% of the 75 degree value).
Hate to have to use conduit, especially since there are many turns (more than 360 degrees) and practically zero clearance for the bend required where cable enters the air handler.
Also wondering: if I run two separate circuits/lines, do I need to tie together to the (2) 240 volt 2-pole breakers in the panel so that they would trip together?
Sorry about the long message but wanted to be precise. Any suggestions?
I want to get rid of the AL wiring because the old 125a breaker shows some possible heat damage (dark spot) and one leg of my main feed coming into the house partially melted down at the meter. Not sure if this was related to the old HVAC system but seems suspicious and I'd reather start fresh.
Everyone seems to agree that 6/2 would be adequate for the 60 amp circuit, even though I thought I read that maximum ampacity of 6 awg NM wire is only 55a (and the max current listed on the heater is 57!)
By the way, the way the air handler is configured, each of the 2 circuits has one 9.6kw heat strip on it, plus one of them also includes the blower. Thus, my question on tying the breakers together in the load center.