choosing a disconnect for heat pump...

Discussion in 'Electrical Forum discussion & Blog' started by Randyj, Jul 10, 2008.

  1. Randyj

    Randyj Master Plumber

    Messages:
    1,047
    Location:
    Alabama
    I'm swapping out a heat pump package unit. The information with the system says to use a 70-80 amp breaker. The circuit supplied to the unit is on a 100 amp breaker with awg #4 copper wire (rated for 70 amps). Inside the unit are 60 amp fuses. I am uncertain as to what kind disconnect to use. I kinda of thought about any would do as long as it would carry the load. However, it seems that the only disconnects I've found in box stores are 60 amp. This is confusing since the unit supposedly is rated at 70 amps. What should I do for a disconnect? And, is the breaker on the circuit the correct one for the wire used (100 amp breaker for 70 amp wire?) Seems to me that the breaker should not be rated greater than the wire....
  2. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    The NEC rules on A/C units are different.

    If the nameplate says use a 70 to 80 amp breaker, then put that size breaker in the panel.

    It may also say what the load is, and the conductors must be sized for that load. They may be larger.

    In the special case of A/C and heat pumps the high starting loads can require the larger breaker, and the unit may be protected by slow-blow fuses that are smaller.

    I'm away from my code so can't cite sections for you.
  3. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    1,006
    Location:
    NY State, USA
    You need a disconnect rated at least what the circuit is. In your case it would be a 100A rated disconnect.
    A small breaker enclosure would be easiest.

    What do you mean the unit says 70-80A breaker? Which one is it?
    What is the ACTUAL draw of the unit?

    I'm not questioning your abilities, but do you think it is time to call in an electrician?
  4. Randyj

    Randyj Master Plumber

    Messages:
    1,047
    Location:
    Alabama
    What seems to have been confusing me is that this unit has four 60 amp breakers in the control box where the supply wires are connected, but the data plate and other info says to use a 70 to 80 amp breaker. I was fortunate to run into an electrician who I've worked with on a few jobs and got his opinion. I had run exactly the correct size wire from the meter/switch box and was told to do exactly what I had deducted... used a 70 amp breaker in an outdoor box for the disconnect. He also told me I could use a 100 amp disconnect switch which was about 5 times the cost. I'm just glad that I'm intelligent enough to know when to ask questions! Still learning after all these years......
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