Adding heat pump to pool sub panel

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Old 09-10-18, 08:58 AM
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Adding heat pump to pool sub panel

I am in the process of adding a heat pump to my pool and want to connect it to my current sub panel. I currently have a 60amp breaker in my main panel feeding a 60amp main breaker in my sub panel. The heat pump requires a 60amp breaker so I am wondering if I need to up my sub panel wiring and breaker for 100amp or greater? I currently have #6 wires , 2 hot, 1 neutral, 1 ground all THWN. Below are some of the specs for my setup.


The sub panel has less than 20 feet of wire back to the main panel.

Main pump - 7.5amps / 230v
Booster pump - 6.9amps / 208v
Stenner pump - 7.7amps / 120v
Pool lights - 4.2amp / 120v
(2) Receptacles - 3amp / 120v
Automation panel - 2amp
Post lights - 2amps / 120v
Misc lights - 3amps / 120v
Landscape lights = 5 amps / 120v

Total amps being used is 41.3

That is the list of current items being fed by my sub panel. I am trying to figure out how to determine the amps for the heat pump. This is what the panel has on the heat pump....

Min Current Ampacity 50.0A
Max Overcurrent Protection Device 60.0A

Supply Voltage: 208min 253max 60Hz

Cpmpressor: 208/230V 37.0 RLA 142.0 LRA 1PH

Outdoor Fan: 208/230V 1.9 RLA 4.6 LRA 1PH

STD Rating: 125,000BTU 80.0F & 80% RH 4.2 COP

Low Temp: 75,000BTU 50.0F & 63% TH 3.0 COP

Any info you can provide from this would be greatly appreciated.

With all of the above do I need to assume the Heat pump will consume 50amps? If so, I guess my answer is I need at least 91.3 amp feed, so going to 100amps would be perfect for my setup? If 100amp is the way to go I assume I will need THWN 3-3-3-5 CU?
 
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Old 09-10-18, 09:07 AM
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Your heat pump requires 40A of power nominally.....so 50A is considered the load.
A 100A sub panel is a good idea. #3 copper is rated for 100A. All conductors feeding a pool sub panel must be insulated. Bare ground is not allowed.
 
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Old 09-10-18, 10:23 AM
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How did you determine the 40A required?

If 100A I plan to use single (insulated) #3 copper. Other than cost do you know of any benefit of going to a smaller ground wire? With my short run of wire it is only a few extra dollars.

What size wire do you recommend for the pool heat pump, #6 copper? If so, I plan to use the existing wire from my 60A sub panel.

Lastly, Is a power disconnect required for a pool heat pump like they typically install on the house units?
 
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Old 09-10-18, 10:32 AM
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Cpmpressor: 208/230V 37.0 RLA 142.0 LRA 1PH
Outdoor Fan: 208/230V 1.9 RLA 4.6 LRA 1PH
Yes....a disconnect in sight of or at the unit is required for servicing.
The #6 are fine for the heat pump.
I would recommend the full size ground.
 
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Old 09-10-18, 10:37 AM
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Thanks for pointing that out. I wasn't sure what the RLA represented.

Thanks again for all your help. I will add the disconnect to my list. My current house pumps do not have a disconnect as the home was built in 1980 but I also plan to add them at some point.
 
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Old 09-11-18, 01:06 PM
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Other than cost do you know of any benefit of going to a smaller ground wire?
1) Ground wire size is specified by code which means a smaller wire meets criteria for safety. Another way of saying that is a larger wire is probably not practically safer.

2) The ground wire size can require a conduit size increase. Conduit is limited to 40% fill by cross sectional area to prevent wire damage and kinking. For example a 100A panel feeder: #3 3 3 8 THWN can run in a 1" PVC pipe (39% fill), whereas #3 3 3 3 THWN would be at 47% fill, requiring a larger diameter conduit. That's more money and possible rework in an existing installation.

The RLA is the rated load amps which is the current draw under nominal operating condition. It's the figure we have to use to design the circuit supplying the motor. Generally the maximum current is about 140% of the RLA. In this motor you can see RLA = 37A and they specified a 50A minimum circuit ampacity to account for the periods actual current exceeds nominal current. This essentially means the motor will usually draw 37A running, but sometimes may go up to 50A. During start-up, the motor will peak at the LRA (locked rotor amps) for a moment and as it picks up speed will settle in closer to the RLA. This is why we often use an even larger breaker size on motors, in this case 60A per manufacturer's Max OCPD specification.
 
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Old 09-13-18, 08:40 AM
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Thanks Ben! Very informative and helpful as always!

I currently have a 1.5" conduit so in my case the 3 3 3 3 is not an issue. I totally get what you are saying and that could be helpful to reduce the size.

Thanks for expanding on the pump specs. I always like to learn more than I "need" to know! I am not one to just except an answer and move one. I typically like to know why it is.
 
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