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I installed a sub panel from a main and am getting arcing on the sub panel neutral bar and neutral circuit wires are becoming discolored in sub panel. I checked for grounding of sub panel neutral bar and there is none. I removed all sub panel circuit wires and still had arcing. I Double checked wiring from main all was good. Voltage check on sub panel bus is fine. What could cause this arcing of neutral bar?

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    Eek. You're going to want to add a diagram or photos to your post. – isherwood Nov 21 '18 at 16:36
  • Are your circuits balanced? Usually the neutral if sized properly and secured under the lugs won't overheat, a heavy imbalance of loads or using 1 neutral with more than 1 breaker (other than MWBC) but then the 2 breakers should be adjacent and handle tied or common trip. – Ed Beal Nov 21 '18 at 17:30
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    Sounds like you have a somewhat serious problem. Please seek some professional help. Overheated electrical wires cause fires. Good Luck. – Paul Logan Nov 21 '18 at 17:41
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Loose lug nuts can lose you a race. Loose neutral lugs can lose you your house

The arcing and failing branch circuit neutral connections in the subpanel are likely doing so because they're loose (i.e. insufficiently torqued). Retightening them isn't enough though -- you will need to get a torque screwdriver in, turn the subpanel off, undo all the neutral screws, cut the burnt ends off the wires and restrip them, then reinstall and torque the neutral lugs to specification with the torque screwdriver.

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Balanced circuits are irrelevant. The arcing is due to poor connections between the wires and bus bars.

If aluminum wire is involved, it's due to failing to use no-ox.

In any case it can also be due to not properly torquing down the screws. It's possible someone was milquetoast and didn't tighten them enough. It's also possible someone overtightened and damaged the wire. This has been such a source of trouble that Code now requires that you use a proper torque wrench to set torques to the factory spec. A garage torque wrench is fine, but many screws need too little torque to be within their normal scale. In that case a mini torque wrench or torque screwdriver is needed.

  • Yeah, you don't need a ft-lb torque wrench unless you're working on industrial switchgear and the likes (stuff upwards of about 250 in-lb or so) – ThreePhaseEel Nov 22 '18 at 14:17

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