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  1. #1
    Join Date
    Mar 2007
    Posts
    135

    Wiring to Air Handler

    Hello All. I hope you had a Merry Christmas/ holidays, etc.

    My boss's house had a fire last month due to aluminum wiring. Other than that, I don't have details.

    I started checking my house and found aluminum 3 conductor 6AWG going to the air handler. An electrician wants to replace this with romex simpull 6AWG copper NM-B.

    The air handler is a carrier FV4 and it has 15KW of heat (part of heat pump system). More data:

    L1/L2 heater amps: 36.2/40.0 min. ampacity 53.8/58.5 max OC protection: 60/60

    L3/L4 heater amps: 18.1/20.0 min. ampacity 22.7/25.0 max OC protection: 25/25

    My first question is that the circuit breakers on the front of the FV4 are both 60 amps. One for L1/L2 and the other for L3/L4. Why would L3/L4 have a 60 amp breaker on the front of the unit? Shouldn't it be a 25 amp breaker as per the label? The breakers in the main panel are 60 for L1/L2 and 25 for L3/L4. I suspect that is ok.

    Second question is about the NM-B 6/2 wire. I checked the website and it is rated for 55 amps. It seems to me this is not enough for L1/L2? This is the scary part because if copper 6AWG is not enough, then certainly aluminum 6AWG is an accident waiting to happen.

    I appreciate your help. I want to be comfortable with what this electrician does.

    K

  2. #2
    Join Date
    Oct 2006
    Location
    So. NH
    Posts
    740
    Quote Originally Posted by kubota View Post
    Hello All. I hope you had a Merry Christmas/ holidays, etc.

    My boss's house had a fire last month due to aluminum wiring. Other than that, I don't have details.

    I started checking my house and found aluminum 3 conductor 6AWG going to the air handler. An electrician wants to replace this with romex simpull 6AWG copper NM-B.

    The air handler is a carrier FV4 and it has 15KW of heat (part of heat pump system). More data:

    L1/L2 heater amps: 36.2/40.0 min. ampacity 53.8/58.5 max OC protection: 60/60

    L3/L4 heater amps: 18.1/20.0 min. ampacity 22.7/25.0 max OC protection: 25/25

    My first question is that the circuit breakers on the front of the FV4 are both 60 amps. One for L1/L2 and the other for L3/L4. Why would L3/L4 have a 60 amp breaker on the front of the unit? Shouldn't it be a 25 amp breaker as per the label? The breakers in the main panel are 60 for L1/L2 and 25 for L3/L4. I suspect that is ok.

    Second question is about the NM-B 6/2 wire. I checked the website and it is rated for 55 amps. It seems to me this is not enough for L1/L2? This is the scary part because if copper 6AWG is not enough, then certainly aluminum 6AWG is an accident waiting to happen.

    I appreciate your help. I want to be comfortable with what this electrician does.

    K
    I would first say that site conditions may change the answer to your question, but generally speaking your electrician, who I assume is qualified and has seen it is most likely correct.
    On your first question the 60A breakers on the equipment only serve as a "service disconnect". The properly sized breakers in the panel protect the equipment and wire.
    Under normal circumstances 6/2 copper NM-B is OK on a 60A breaker.

  3. #3
    Join Date
    Oct 2008
    Location
    Coming to a town near you soon
    Posts
    762
    Use this at your own risk.


    http://www.csgnetwork.com/wiresizecalc.html

  4. #4
    Join Date
    Nov 2000
    Location
    Upstate, SC
    Posts
    2,914
    6-2 copper w/ ground is typically ran for 10 kw heaters, but technically, it may or may not be large enough. The NEC table 310.16 spells out the capacities. 6 awg would be good for 55 to 75 amps depending upon its type, but this is at 86 degrees F. If you derate for temperature, it could be much less if it is running through an attic. The table also makes no allowances for distance, so once you calculate the distance and take that from the equation, it will be even less. In your case, I'd get rid of the alum wire and wouldn't be worried about 6 awg copper. The connections are usually where the problems start on any wire, but if it is a long distance through an attic I might consider 4 awg.

  5. #5
    Join Date
    Mar 2007
    Posts
    135
    Thank you for the replies.

    I think I have a good grasp on what the electrician is talking about now.

    Have a great new year.

    K

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