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A customer of mine had a friend wire his basement. He did a neat job, but when I opened up the mailnpanel to add a circuit, I noticed he had installed ground bars and separated them from the neutral bus bars. The neutral and grounds are not connected at all (like you would do in a sub panel). I talked to the guy about it and he said, "it is an isolated ground system which is better for electronics." I cannot find any info on where this is legitimate. Let me know your thoughts. Thanks.

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    What make and model is the panel in question? Also, I take it you're 100% sure the main service disconnect lives in that panel? – ThreePhaseEel Sep 11 '18 at 1:26
  • Is neutral bonded to ground? If so where? – Tyson Sep 11 '18 at 1:28
  • Thanks for getting back with me. Panel is a Square D Homeline. It is a 200 amp main panel with the service disconnect in the panel. Neutral is not bonded to ground. They are isolated from each other. – MitchBray Sep 11 '18 at 1:45
  • Basically it is a main panel wired like you would do a sub panel, with the neutral and ground separated. The person who did the work is not an electrician and I need to know if this is code compliant and if not is it unsafe. – MitchBray Sep 11 '18 at 1:49
  • Is the main breaker in this panel? Is the incoming power feed 3 wires or 4? – Harper Sep 11 '18 at 2:10
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This isn't what "isolated ground" means in the NEC

What your customer has is not an isolated ground -- it's an ungrounded system, which is only permitted for specific industrial applications in the NEC where electrical system availability is critical and ground-fault detection can be provisioned separately. In an ungrounded system, there is no neutral wire, just hot wires and an equipment grounding wire -- this doesn't work well with the split-phase neutral system, so 120/240V split phase services are required to be grounded (neutral on this type of service is grounded at the transformer anyway, for that matter).

An isolated ground system, on the other hand, has a normal neutral/ground bond, but runs a dedicated ground wire to the receptacle ground contact from the main bonding point, perhaps via isolated busbars on its way, but not bonded to the main equipment grounding system; likewise, the receptacle ground contacts on isolated ground receptacles are isolated from the receptacle yoke.

As to fixing this...

Go to your local electrical supply house and ask them for a Square D 4028345850K, as per this FAQ entry, then, with the main breaker turned off, install it into the mating screw hole on the loadcenter's neutral tie bar (the metal busbar behind and below the main lugs or main breaker load connections that connects the two neutral bars together).

  • Thanks. I'll let the homeowner know. I'm going to recommend he get a licensed electrician to do the work. – MitchBray Sep 11 '18 at 10:47

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