Wiring in Geothermal Furance/AC unit


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Old 10-17-07, 07:50 PM
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Wiring in Geothermal Furance/AC unit

I'm about to wire in a new Hydron Geothermal unit. I'm told I need a 50amp and 30amp circuit to the unit (it has the heat pump, circulating pump, a blower and a backup electrical element). I'm not sure how those devices are broken up within the unit.

I assume I should have a disconnect of some sort. On the 50amp, I'm planning to run 6/3, on the 30amp probably 10/3. I'm guessing it'll be cheaper to do that than to have a sub-panel there - the runs should only be about 50 feet. I'm looking for suggestions on the type of disconnect to use - should I drop two small single-breaker boxes in there, or is there something cleaner than that for that type of amperage? Also, I assume I can use NM-B as long as I have, say, a flexible conduit coming down from the ceiling?

Thanks for any advice you can give regarding the above, and what I've overlooked.

Thanks
 
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Old 10-18-07, 07:30 AM
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Originally Posted by csharp
I'm told I need a 50amp and 30amp circuit to the unit (it has the heat pump, circulating pump, a blower and a backup electrical element).
Determine if these are 240V circuits or 120/240V circuits. They are probably plain 240V, but with a blower and circuitry they could also require 120V.

I assume I should have a disconnect of some sort.
If you have line-of-sight to the panel box, the breaker can count as the disconnect. Otherwise, pick up some 60A air conditioner non-fused disconnect boxes; they are about $10.

On the 50amp, I'm planning to run 6/3, on the 30amp probably 10/3.
If these are 240V circuits (no 120V), you can run 6/2 and 10/2 respectively. The */3 cable is required only if the unit(s) need 120V in addition to 240V.

Also, I assume I can use NM-B as long as I have, say, a flexible conduit coming down from the ceiling?
NM-B is fine in the basement ceiling. I would use EMT from the ceiling down to the unit; flex does not really provide much protection.
 
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Old 10-18-07, 08:02 AM
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Thanks for your reply! I was eyeing these A/C disconnect boxes, glad they'll work. $7.75

Would be nice if there was a 2x60 type of deal, so I wouldn't need two boxes, but I don't see one. Will these work regardless of needing 120 (neutral connector) or not?

I was curious - is a 50A breaker very common? If using #6, any reason I can't use a 60A breaker? The unit itself isn't fused. Also wondering if I'll be able to fit #6 into one of these breakers directly.

Also, can I bring the NM directly into the conduit from the ceiling, without a box or anything? Just find some kind of fitting to protect the wire from the edge of the conduit?
 
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Old 10-18-07, 08:28 AM
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Originally Posted by csharp
Will these work regardless of needing 120 (neutral connector) or not?
Yes. The neutral does not need to be switched.

I was curious - is a 50A breaker very common? If using #6, any reason I can't use a 60A breaker?
A 50A is very common. The breaker should be no larger than the "max OCPD" rating for the appliance, and no smaller than the "min circuit ampacity".

Also wondering if I'll be able to fit #6 into one of these breakers directly.
It will fit just fine.

Just find some kind of fitting to protect the wire from the edge of the conduit?
Yep, you just need a fitting on the end of the conduit to cover the sharp end; you could put a box with a romex clamp too.
 
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Old 10-18-07, 10:32 AM
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Thanks. I was curious - some of the other wires could go in the wall (haven't got sheetrock on it yet). Is there a clean way to come out of the wall, into conduit? I could come into the back of a box, I guess, but I've never understood how you're supposed to secure the wires coming into the back of a box that's wall-mounted. Is there some type of fastener that I'm overlooking?
 
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Old 10-18-07, 10:57 AM
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You can go into an LB fitting or into the back of the box. Just use a regular Romex box connector, but attach it before mounting the box to the wall.
 
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Old 10-18-07, 11:10 AM
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I assume you mean with the clamp facing the outside of the box? So I just need to cut away some sheetrock for it to fit into the wall basically? Seemed kinda sloppy, but I guess that's the way..

Also, it looks like I need to run a 5amp wire from the unit to the pump (240). Says it "may need to be fused". I'm not sure whether or not it does need to be in Minnesota. Are there cheap little boxes made for 5amp/240, or should I just use a full sized fused disconnect box and a 5a breaker?
 
 

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