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-   -   A/C inside Blower unit and ouside condenser grounding (https://www.askmehelpdesk.com/showthread.php?t=272306)

  • Oct 22, 2008, 09:26 AM
    abcsalem
    A/C inside Blower unit and ouside condenser grounding
    My house is 20+ years old. While working in the main electrical panel, I've noticed the A/C wiring for the inside and outside units have their ground wire cut off at the entry to
    The main panel, and therefore not connected to the ground bar. After further examining
    The inside and outside units, I found that the ground wire was cut off at the entry
    To the unit and not connected. The power to these units are 240v, therefore they
    Have HOT: Red&Black, Neutral: White wires. I shut the power to these units,
    And measured the resistance from the white wire to the chassis, it reads close to zero.
    At this point I can only assume that since 20 years ago, there was no code for
    Grounding the 240v units, the white wire is doing the job of both Neutral & Ground.

    Question: By code Neutral & Ground are bonded together in the main panel. If
    I try to add a ground wire from the main panel to these A/C units, how do I
    Wire it in so that, there would be no bonding between Neutral & Ground
    At the unit?

    I am assuming that bonding Neutral & Ground any place other than main panel is
    Against code, am right?

    At this point I am not clear how these A/C units are wired internally for the
    Neutral wire. Any idea how 240v A/C units are wired to handle the ground
    And Neutral wire so that they won't be bonded together at the unit. Can I
    Rewire the inside of these units to fix the Neutral & Ground issue
    Or is this a task for the manufacturer of these units
    And they should a have provided terminals for the Red, Black, White, Green.
    These units are 20+ years old, and NEC was different back then.
  • Oct 22, 2008, 11:55 AM
    KISS

    Your going to have to fill in a lot of blanks. Not sure what kind of furnace you have: oil, gas, electric, heatpump

    For typical outside units, only L1, L2 and ground are required for 240 operation.

    Indoor units are primarily 120 V except when electric heat.

    Is it possible that someone used the white as a ground, but didn't label it properly?
  • Oct 22, 2008, 01:15 PM
    abcsalem
    The inside unit is only electric. It only has the cooling modules in it. NO heating.
    The job of the inside unit is to blow air on the cooling elements that is
    Copper piped to the outside condenser unit.

    As far as the inside unit wiring in the main panel goes, there is a dual pole breaker
    With a common trip. Each of the breaker is marked as 15A. Red wire goes to
    One leg, and Black wire goes to the other leg. The white is connected to the
    Ground bar, and the Ground bare copper wire is cut off at the entry to the main panel.

    Is it possible that, the inside unit is 120v, and each of the dual-pole breaker
    Is only supplying 120v to a circuit within the inside unit? Since they used
    Dual-pole with a common trip, I assumed it was a 240v circuit.

    I think the outside units were almost wired the same way, with the following
    Exceptions: inside the main panel, the white wire goes to Neutral bus bar, and
    The dual-pole breaker with common trip is marked as 40A each.
  • Oct 22, 2008, 01:22 PM
    KISS

    So, it appears that they used white for ground. If so, it should be taped green. In the main panel ground and neutral are usually tied together, so white can either be a ground or a neutral. 240 stuff does not always require a neutral. It does require a ground.
  • Oct 24, 2008, 07:02 AM
    abcsalem

    Please bare with me as I am trying to understand how 240v circuits need to be wired to code.
    So for 240v circuits, the return current (by code) is done over
    The ground wire rather than the white Neutral wire?

    It seems odd and dangerous to me that code would allow this type of installation.

    Even though service Neutral and Ground wire are bonded
    Together in the main panel, I always thought that for safety
    (and by code), we wire everything to return current back
    To the main panel on the white wire, and ground everything.

    If I understand you correctly, the inside and outside A/C units
    Are almost wired correctly, and all I have to do is to either
    Place a green tape on the white wire and/or remove the white
    Wire from the Neutral bus bar and place it under the ground bar.

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