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Commons Clamped together


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Saw a sub panel back fed by a 100amp breaker in the main. The common from the sub and common from the main where clamped togther in the main panel. Is this okay? I ask because we came across serveral outlets powerd by the sub that were not reading a ground. Could the two commons being together cause a false read?



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Now I think I'm forming a picture; the grounded (neutral) conductor from the sub-panel is secured under the same lug in the main panel as the grounded conductor from the service entrance.

As far as I know, it's not OK to do that. First, a lug has to be rated for two conductors and second there is rule that grounded conductors will each have their own little seat on the bus. There should have been another lug somewhere on the neutral bus in that main panel to which the grounded conductor from the sub-panel feeder can be attached.



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