Adding a Heat Pump to an Existing Residential Service

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Amps

Electrical Contractor
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New Jersey
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Electrical, Security, Networks and Everything Else.
Hello and thank you in advance for your input on this.
I'm looking at a single family residential 100A service, a Murray main panel, 1980's vintage. It's in a very old 1800's house and various circuits have been added over the years. The 20 circuit Murray panel has a 100A main breaker. There is an electric cooktop-40A breaker, wall oven-40A breaker, dryer-30A breaker, laundry-20A, gas furnace15A. Plus general lighting and kitchen small appliance circuits. There is a spare 30A 2pole breaker that used to go to a 2nd floor dryer that is abandoned.
The owner plans to add a heat pump for AC and heat, with a back up gas furnace. The heat pump specs are shown below. I was considering using the spare dryer circuit, changing the breaker to 30A HACR type, installing the #10awg copper circuit and outdoor disconnect. Once I received the specs,I noticed the L.R. AMPS at 72.2.
Could this trip the 100AMP main breaker in the event some other loads are on, such as wall oven, dryer, etc? Due to the cost of the HVAC work the owner would like to avoid upgrading the service to 200A at this time, but it is a future plan. I know that LRA is the start up current happening in fractions of a second, but I am leery about it happening when other loads are on.

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The LRA wouldn't (shouldn't) last long enough to cause a problem. Your 30A circuit breaker would (should) trip before the 100A if there were ever a problem.
 
The unit only draws less than 14 amps when running so there should not be an issue with adding it to the existing panel. How old is the existing 30 amp circuit breaker? All modern breakers are automatically HACR rated.
 
Rock86 said:
The LRA wouldn't (shouldn't) last long enough to cause a problem. Your 30A circuit breaker would (should) trip before the 100A if there were ever a problem.
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Thank you. I was thinking that the 30A would trip first, even when other loads are on at the same time. Just wasn't sure.
 
infinity said:
The unit only draws less than 14 amps when running so there should not be an issue with adding it to the existing panel. How old is the existing 30 amp circuit breaker? All modern breakers are automatically HACR rated.
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I would replace the old 30A with a new one. Thanks.
 
Amps said:
I was considering using the spare dryer circuit, changing the breaker to 30A HACR type, installing the #10awg copper circuit and outdoor disconnect.
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You can use #12 cu, because the MCA is only 18a.

Amps said:
Could this trip the 100AMP main breaker in the event some other loads are on, such as wall oven, dryer, etc?
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Absolutely possible.
 
Realistically sounds like a calculation based on article 220 is required to determine the size service the NEC requires for the home. Unless you can get the peak demand history on the meter (Unlikely for a residential service) from the last 12 months, add 25% to the peak demand and add your new load to determine proper service size per 220.87. Tripping the 100A breaker is one thing , having a properly sized electric service is another, but both equally as important.
 
I agree and thank all of you for your comments. Decided to upgrade the service to 200A.
 
You did not show the AC specs or SEER or HSPF numbers. Off the top of my head, would suggest to the HO an inverter type heat pump, would be higher SEER, might cost more, but would save the difference in a year or so in NJ.
Suggest to HO to discuss that option with his HVAC contractor. Then no inrush either.
Normal compressor the HO may find lights filickering objectionable in a neighborhood with 100 A services which implies only 25 kVA or so distribution xfmr. ?
 
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