Breaker and wire size for pool heat pump - MCA, wire and breaker size.

Discussion in 'Electrical Forum discussion & Blog' started by JerryR, Feb 28, 2014.

  1. JerryR

    JerryR Member

    Messages:
    244
    Location:
    Florida
    Were going to install a Hayward HP21104T 5 ton pool heater heat pump. Installation instructions are here;
    http://www.hayward-pool.com/pdf/manuals/heatpro 4T installation.pdf.

    Specs call for Maximum 60 amp with "Minimum Current Ampacity" of 35 amps. What I have been reading is that wire needs to be sized the Minimum Circuit Ampacity of 35 amps yet maximum (not minimum) "fuse" size of 60 amps

    There is an article that describes why here:
    http://www.mikeholt.com/mojonewsarc...ning-and-Refrigerating-Equipment~20040102.htm

    Installer said he typically installs with #8 wire with 50 amp breaker. The outdoor supply panel already has an unused 50 amp breaker in it. The whip length needed is only about 10 feet. I'll probably run #6 whip and keep the 50 amp breaker.

    What do you all think?

    Specs for the HP21104T are in the far right column.

    [​IMG]
    Last edited: Feb 28, 2014
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,534
    Location:
    North Carolina
    A #10 THW and a 60 amp breaker will meet the code. A #6 THW is a little over kill.
  3. nhmaster3015

    nhmaster3015 Master Plumber

    Messages:
    836
    Location:
    The granite state
    What he said. Don't get carried away.
  4. JerryR

    JerryR Member

    Messages:
    244
    Location:
    Florida
    Thanks for the replies. I see the #10 THW is rated for 35 Ampacity per chart http://www.usawire-cable.com/pdfs/THW.pdf

    A few more questions;

    1. Does the wire size need to handle 125% of listed Ampacity? If so then 35amp X 1.25 = 43.75 amps.

    2. What size THW ground wire should be run in the whip?

    3. Bonding. Currently it looks like #10 bare solid bond wire was used between pool, screen enclosure, filter pump and spa pump back when pool was installed in 1997. From memory I thought #8 solid was required for code.

    Thanks in advance.
    Last edited: Mar 1, 2014
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,642
    Location:
    Cave Creek, Arizona
    quote; A #10 THW and a 60 amp breaker will meet the code

    How would a 60 amp breaker on a wire rated for 35 amps "meet the code". The wire capacity dictates the maximum breaker size.
  6. JerryR

    JerryR Member

    Messages:
    244
    Location:
    Florida

    HJ,

    I know. It sounded crazy to me also. I always thought #10 should be connected to maximum 30 amps as when wiring electric water heaters, Air compressors etc.

    After talking to the pool pump installer and doing some research, I found that the rules are different for "electrically driven air-conditioning and refrigeration equipment that has a hermetic refrigerant motor-compressor", Now household appliances as room air-conditioners, household refrigerators and freezers, drinking water coolers, or beverage dispensing machines are not included in this rule.

    Article 440, Air Conditioning and Refrigerating Equipment.

    Conductor Sizing:
    Dictated by the listed "Minimum Circuit Ampacity" This pool heat pump lists this as 35 amps, which #10 THW is spec’d for. .

    Circuit Protection
    The short-circuit and ground-fault protection device for motor-compressor conductors must be capable of carrying the starting current of the motor. Also, the protection device cannot exceed 175 percent of the equipment load current rating. If that is not enough to handle the starting current of the motor-compressor, you can use the next larger protection device if it does not exceed 225 percent of the motor-compressor current rating.

    So #10 wire (35 ampacity) and 60 amp breaker (27 amp compressor current x 225% = 60.25) meets code.

    I'll still probably go with #8 THW and use the existing 50 amp breaker for now since the cost difference is not much with a 10' length and I will feel better. if the 50 amp breaker can’t handle the load for compressor start up I'll just install a 60 amp breaker.
  7. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    Because it DOES Meet the code. The wire size does NOT always dictate the breaker size.
    Read up on motors and A/C-refridgeration equip. You'll see what I mean.
  8. ActionDave

    ActionDave Electrician

    Messages:
    346
    Location:
    Colorado
    Not all of the time. There are exceptions.
  9. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,150
    Location:
    Houston, TX
    A #8 would be better to use, Even if code allows a smaller conductor.

    I thought it was a 50 Amp breaker ?
  10. JerryR

    JerryR Member

    Messages:
    244
    Location:
    Florida
    Yes, currently I have an unused 50 amp breaker in the pool service panel. Installation manual calls for MAX 60 amp protection to handle compressor start up current. There should be no legal or safety issue using 50 amp breaker since it doesn't exceed 60 amps. Worst case the breaker trips on start up and I then install a 60 amp breaker.
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,642
    Location:
    Cave Creek, Arizona
    #10nwire and a 50/60 amp breaker might be good outside, but I would not want a #10 wire running through my attic if were attached to anything bigger than a 35 amp breaker. I can visualize the motor locking up and drawing 45 amps, which would not trip the breaker but WOULD melt the insulation on the wire.
  12. JerryR

    JerryR Member

    Messages:
    244
    Location:
    Florida
    We agree. There is #6 in the attic, from the main panel to the pool pump sub panel mounted on the outside wall. I was planning on using #8 for the 10 foot distance from the sub panel to the heat pump.

    I can't find short lengths of of THW. I have an electrician lined up to wire it properly. Installation us scheduled for Monday.

    JR
  13. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    This is not a scenario that will ever likely happen. If the motor did lock up the motor will overheat and shut down long before any conductor damage occurs. This is why there are exceptions for things like motors, welders and A/C~refer equipment.

    If code allows #10 on a 50A breaker in this case what are you afraid of? You are letting the fear of the unknown get the better of you. You need to think outside the convention of what you've always been told, ie: #10 on no bigger than 30A.
  14. bluebinky

    bluebinky Member

    Messages:
    393
    Location:
    Santa Clara, CA
    I agree with HJ. What is ikely isn't what's important -- what is reasonably possible is what matters... The code is just a minimum.
  15. ActionDave

    ActionDave Electrician

    Messages:
    346
    Location:
    Colorado
    Petey is right. The A/C unit is protected from overcurrent internally. If it were to lock up the overloads would trip or the motor would burn up long before the wire feeding it could be damaged. The breaker is there to provide short circuit and ground fault protection only, and in the event of one there is going to be a thousand amps flowing so a bigger wire or a smaller breaker wouldn't be any safer.
  16. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    I hear this all the time. Thing is, it's almost always uttered by folks that don't know the code, or know it just enough because it's "what they were told". Typically, jobs they do are so overbuilt it's not funny, mostly to cover their ignorance.

    Do I wire completely to code minimum all the time? Of course not. But code minimum is 100% SAFE. Period, end of story.
    The thing with code minimum is more one of convenience. Like putting a refer on with kitchen counter circuits. It's allowed, but can be inconvenient.

    Do you guys honestly think the conservative NEC would allow #10 on a 50A breaker if it were potentially unsafe???
  17. bluebinky

    bluebinky Member

    Messages:
    393
    Location:
    Santa Clara, CA
    Uh, really?

    Strange how my garage/shop in Texas (that clueless me built) survived the last big storm completely intact while several smaller code-minimum buildings nearby were toast.

    Here in my CA house, the lights don't dim in my living room when the fridge turns on any more. Why is that? The place was originally wired code compliant...
  18. ActionDave

    ActionDave Electrician

    Messages:
    346
    Location:
    Colorado
    Building codes, especially in Texas, is a whole lot different than NEC.

    Lights not dimming has everything to do with the Power Company supply, size of service conductors, number of houses on the same transformer, personal perception, type of light bulb in the fixtures....and the list goes on. Not included in said list is the wiring inside the house.

    I have a truck that gets me back and forth to work, to the school to pick up kids, over to the folks house for dinner on Sundays; nothing special about it at all. It has all the safety features of any other vehicle on the road. Extra heavy duty tires won't make it any safer.
  19. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,150
    Location:
    Houston, TX
    A person really needs to size the wire for the task of the wire.

    On a long run a bigger conductor should be used.

    A 5% voltage drop may be acceptable for some applications, but some Inductive loads may not tolerate large voltage drops during start-up.

    Wire sizing that NEC recommends may be safe for the wire, but not the appliance when its built in overload protection keeps trying to restart on low voltage conditions.

    A simple calculator can give a best guess for the wire size, based on its length and required current.

    http://www.calculator.net/voltage-drop-calculator.html


    10 Feet of #10 can handle a lot of power before it gets Hot.
  20. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    Do tell. How would bigger wire help with this?
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