Pool Heat Pump

G

Garmaster

Member
Location
Kill Devil Hills NC
Occupation
Electrician
Question on wiring a pool heat pump. The Mca is 22A and max breaker is 35A. There is a #12 nmb circuit available. Am I able to size the wire on a heat pump based on using the minimum ampacity but sizing the breaker to a larger breaker size? In table 310.16 in the 60* column it says #12 is good for 25A. So basically what I am asking is can I wire this pool heater with #12 and use a 30A breaker or 25A breaker?
 
Eddie702 said:
If the circuit is NMB #12 it can't be protected at over 20 amps. You would have to use another wiring method.
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It can be protected at greater than 20 amps for things like AC and motors, but it cannot supply a load greater than 20 amps. The minimum circuit ampacity is 22 amps.
If the MCA would have been 19.9 amps and the maximum OCPD 35 amps, you could use 12 AWG NM for that circuit
 
I was looking at a 2008 code book and it says 25A. I have a 2014 codebook on my phone that says 20A. I didn’t realize the code had changed. Guess I need to get a more current codebook. I don’t look at it very often, pretty much do the same types of jobs over and over. I was trying to avoid a 100’ run all the way around the house.
 
Garmaster said:
I was looking at a 2008 code book and it says 25A. I have a 2014 codebook on my phone that says 20A. I didn’t realize the code had changed. Guess I need to get a more current codebook. I don’t look at it very often, pretty much do the same types of jobs over and over. I was trying to avoid a 100’ run all the way around the house.
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The problem is that the NM cable is limited to a 60°C ampacity or 20 amps. If the cable were MC or conduit and wire then you could use the 75°C ampacity of 25 amps.
 
I believe the general rule that limits 12 AWG to 20A is 240.4(D) not so much tables in 310, and the section that allows it for HVAC 240.4(G)
 
pipe_bender said:
I believe the general rule that limits 12 AWG to 20A is 240.4(D) not so much tables in 310, and the section that allows it for HVAC 240.4(G)
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Yes 240.4(D) would typically apply to #12 circuit conductors but it wouldn't apply in this case due to 240.4(G) as you've mentioned. That leaves us with a 60° C limitation from 334.80. For some other wiring methods the 75° C ampacity of 25 amps from T310.16 for #12 can be used.
 
don_resqcapt19 said:
It can be protected at greater than 20 amps for things like AC and motors, but it cannot supply a load greater than 20 amps. The minimum circuit ampacity is 22 amps.
If the MCA would have been 19.9 amps and the maximum OCPD 35 amps, you could use 12 AWG NM for that circuit
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Ok. So it can't supply a load of over 20 amps. The MCA is 22 but the "load" might be under 20 amps as it would include 25% of the larges motor which would be the compressor. For instance if the compressor was 16A and the condenser fan was 2 amps=16 x 1.25 + 2=22MCA but the actual load is 16 + 2=20.
 
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