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new apartment subpanel

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  • new apartment subpanel

    I planning to run 60 feet of 6-3 BX to a new subpanel. I will be putting a 50 amp breaker on both ends of the BX (one on the 100 amp feeder panel and another 50 amp on the other end at the sub panel). I would like to know if this is correct thing to do? Is the 50 amp breaker too much for a 50 -60 feet run considering resistance obtained by the length of the BX. Also is a 6-3 BX ok? (The steel amour will act as the ground for the sunpanel).
    Any input will be greatly appreciated,...Thanks!

  • #2
    Re: new apartment subpanel

    What you're proposing is fine. You do not need the 2nd 50amp breaker in the sub panel itself, you can have it as a means to disconnect the whole panel except for the mains, but it is not required. In the subpanel itself you must also make sure the Neutrals and grounds are NOT touching. If there is a lug that goes from the neutral bar to the panel box, you must remove it. Other then that you're fine. Derating at 50' is not even considered. As a matter of fact, that 6/3 is probably good for 65amps.

    Depending on the knockout you enter your BX into, you may also want to consider using a bonding bushing, which is a metal bushing that has a hole in it and a screw that you can put a piece of wire in to, and from there to the ground bar to get a really good ground on the BX armour.


    • #3
      Re: new apartment subpanel

      Thanks for the reply!


      • #4
        Re: new apartment subpanel

        A) Be sure the BX (Armored cable) has a bare wire ground conductor inside it. Make sure of this before you buy it.

        B) As for the second 50 Amp 2 pole breaker in the sub-panel it's not needed but it's fine if you want it. You might also think about a 2 pole 60 Amp fused enclosed safety switch.
        Normally sub-panels are connected up as lug feed. The breaker in your main panel serves as the main.

        C) Be sure to get and use proper connectors, lock nuts and bushings.

        Ask your electrical supplier about aluminum jacket armored cable. It's lighter weight and easier to work with than steel jacket. Do be sure the conductors are copper.

        As for 6-3 being able carry 50 Amps, that's no problem. Even if 100 feet you'll be fine.

        Do not bond-connect neutral and ground together and use both the ground conductor and the jacket for grounding. If you really want to go all out, you can ask if they have 6-4 BX and then use green tape on the ground conductor. That would really give you a good ground, but it is overkill.


        • #5
          Re: new apartment subpanel

          Thanks for the input. Is there a specfic panel that I should buy? I'm talking about the type (main lug vs main breaker) and rating (100 vs 125 A)? Is there such a thing as installing an over rated panel box?

          Another area of concern is the 2 main panels in my basement (2 family home). One panel has a grounding cable from the neutral bar to the water supply line and the second panel has a grounding cable connected in series to the neutral bar of the first panel. Should there be 2 separate grounding cables connected the water supply line or 1 is enough? Thanks!
          Last edited by falomany; 03-13-2008, 09:18 PM.