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#199780 03/08/11 05:42 PM
Joined: May 2003
Posts: 1,158
I am looking at installing a sub panel for an existing heat pump. The HVAC contractor just extended an existing AC circuit but didn't noticed that the circuit was also used for the range.They never looked in the panel to see the 30 amp range circuit piggy backed with the AC circuit.

The heat pump specs say a min 21.5 amps and max breaker size is 35 amp. It looks like the feeder is #12 to me. I couldn't get the arc shield off the HP disconnect to confirm as I have to reposition the shield to get it off.

I assume this whole circuit needs to be 30 amps

dougwells #199792 03/08/11 11:05 PM
Joined: Mar 2004
Posts: 947
twh Offline
I agree, 30 amps.

dougwells #199793 03/08/11 11:28 PM
Joined: May 2003
Posts: 1,158
Any Idea if the loomex with the red jacket and a black and a red conductor is 12 Gauge the last stuff i seen was only 12 gauge and they used that inside the whip ent from the disconnect

Last edited by dougwells; 03/08/11 11:28 PM.
dougwells #199810 03/09/11 12:19 PM
Joined: Jul 2005
Posts: 183
The red jacketed loomex is available in mutliple gages, so it could be 14, 12, 10 etc - you would need to confirm.

As far as the subpanel size, you may be able to get away with 30 amp, but the specs say max overcurrent of 35 amps, so if a 30 amp overcurrent did'nt hold on start up, you may have to consider time delay overcurrent or non time delay overcurrent and be prepared to go up to 35 amps, which means the sub panel would have to be rated accordingly.

dougwells #199815 03/09/11 12:45 PM
Joined: May 2003
Posts: 1,158
I am putting in a 60 amp sub panel well a 125 amp load center feed with a 60 amp breaker.

dougwells #199823 03/09/11 05:06 PM
Joined: Feb 2011
Posts: 56
Check out Table D16 (app D) under 'single phase all types'. Under circuit breaker of 35A, it shows an FLA of either 14 or 15A (if these match the heat pump)
Picking the bigger one...15A X 1.25 is the max conductor ampacity. Which is 18.75A
T2 says #12.

The table also gives fuse sizes. If needed.
I'd use a 30A to feed it (cause it worked before)

dougwells #199833 03/10/11 02:33 AM
Joined: Jul 2005
Posts: 183
30 amps on the range is a little unusual also, is it standard 50 amp range receptacle, with #8 copper to it?

dougwells #199834 03/10/11 02:54 AM
Joined: May 2003
Posts: 1,158
For some reason sometime in the early 70's some house's where wired with 10/3 for the range and on a 40 amp breaker.
If we do a service upgrade then we need to change the feeder out to a 8/3 if that is the case.
Same with a mobile home that may need a CSA re certification if it is a 10/3 feeder

dougwells #199854 03/11/11 01:59 PM
Joined: Jun 2004
Posts: 1,273
Heat pumps, per se, almost never use that much juice...

The killer is that it is as common as dust for them to have FIELD INSTALLED resistance heater boosters, one or two.

If the climate is somewhat mild only one strip will be slipped in.

As you go north, expect to find two resistance heaters.

Neither of them will be listed on the outside label, which will only show the basic heat pump demands.

So until you open the box up and inspect for the boosters you don't know what you've got.

Personally I've never seen a heat pump without boosters.

The boosters ( for cold, cold days ) are electric pigs and will typically require multiples of the base demand.

If your HP needs, say, 20 amps then its first booster would lift that to 40+20=60 amps.

The only time boosters get omitted is if the climate never reaches freezing. Never.


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