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Proper wire/size for heat pump air handler

Posted by jasmar (My Page) on
Sat, Dec 28, 13 at 19:07

cross posted in heating and air, but I thought as it pertains to electrical this may be as good a forum:
When installing a heat pump system that has an air handler with emergency type heat strip(s) installed with two breakers in the unit what type of wire should be used to feed power to it? Assume that it replaces either a smaller heat pump system or a traditional electric heat air handler that had a single power feed. Is it better to add a breaker to the main panel and feed the second breaker/disconnect in the air handler or is it better to uprade the wiring and use the appropriate single feed kit for the air handler so both breakers can be fed from one breaker in the main? If going that route what type of wire should be used? In my case there is a 30A breaker and a 60A breaker. My preference would be to protect it at the main panel with a 90 or 100 amp breaker and install a single feed but that would require #3 wire and I am only aware of THHN in that size. Air handler is is about 50 feet from the main panel. Conduit is not totally impossible but would be quite a job. Could I use SE type cable? I am double posting this in electrical.
Thanks, J

Follow-Up Postings:

RE: Proper wire/size for heat pump air handler

Your first step is to read the manufacturers information. If it says run two circuits, you are obliged to run two circuits. You can not just put in a single breaker regardless of how big you make the conductors. If you use SE, you need to watch for a few things: first you must have an appropriate sized grounding conductor in the cable you are using, second if Aluminum (most are) make sure the terminals on the device take aluminum, third remember that when running SE interior you must not exceed the 60 degree (after derating) ampacity even if the cable is approved at 75 or 90.
Note that USE is not permitted for interior use.

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