I've found a number of these type of questions in here and I thought I'd post my own, with what I *think* my solution is.

I have two geothermal units

The first Geo unit has this...
Min CKT Ampacity = 25.6 A
Max HACR = 35 A

The second unit has this...
Min CKT Ampacity = 29.6 A
Max HACR = 45 A

I understand I need to get HACR breakers for the motor start. I'm looking for what size wire I'll need.

For the first unit, the documentation says MIN wire size is a #10 at 60C, but it also says as a subnote "Current carrying capacity of the wire used must not be less than the fuse/breaker size used".

I'm guessing that just means if I use #10 wire, that I should stick a 30 amp breaker in.

For the second units the docs say MIN wire size is again #10. It just seems that with the MIN circuit being 29.6 amps, I should have a bigger breaker there.

I found an article that talked about sizing the protection at 175% of the equipment load current rating (up to 225% if the starting current trips the 175%).

That sounds to me like I can run a 40 amp breaker with #10 wire to that second unit. I think I'll end up running #8 THHN to both units to be on the safe side, but I thought I'd ask.

John


John

John,

One important measurement you are leaving out, how far away from the breaker panel will the units be?

Eric D

Quote:

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Originally Posted by Eric D

John,

One important measurement you are leaving out, how far away from the breaker panel will the units be?

Eric D

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About 15 - 20 feet as the wire runs

Based on the statement "Current carrying capacity of the wire used must not be less than the fuse/breaker size used"., which I assume is from the manufacturer, Unit #1 needs min #10 wire on a 30 amp breaker, and #2 needs #8 wire on a 40 amp breaker.

If the breakers chosen do not start the units, you normally would be allowed to go up to the next size breaker, but because of the statement above, the wire size will need to increase.

Is there a limit (besides what I can shove through) for wire inside 3/4" flexible aluminum conduit?

I have to run a 50 AMP (6/2) and 25 AMP (10/2) wire for one of the geothermal units backup heat. The knockout nearest the power lugs on the unit is 3/4", but I wasn't sure if I could run them both through it.

John

Every raceway has a limit of the amount of conductors allowed to be pulled through, typically only 40% fill is allowed based on the wire size and type of insulation.

This will be listed in Table C.3 in Annex C of the NEC.

Here you will find how many wires of the same size wire and insulation.

For combinations, calculations must be done based on the circular mil area of each wire, and do not exceed 40% of the CMA of the inside dimension of the raceway.

Since you need 2 #6 and 2 #10, one more #10 is needed for an equipment ground.

3/4" FMC is just enough for the wires you need, assuming all THHN insulation.

The power feed on your geothermal unit should be a low knockout for your contactor(compressor) and a knock out around the top of the system for aux heat, two different locations for L1 and L2.