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sub panel ground bars and grounding metal boxes

5458 Views 6 Replies 6 Participants Last post by  tombs31
2 things i've always wondered about. I'm no electrician but why does a metal box need a ground tap in it? If you attach the circuit ground to the receptacle screw, its attached to the metal strap which you run metal screws through into a metal box. Isnt this in essence achieving the same thing? And why does a sub panel need the grounds seperate from the neutrals but the main panel doesnt? Electricians get tired of answering my questions so i'll spread some out here. :laughing:
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As 480 stated if the device is removed then there is no ground. Also IMO if the device is grounded but the box is not and the short to ground occurs in the box then you are relying on the device screws to complete that short to ground. If the device is loose for any reason then the box itself may remain hot without the breaker tripping.
It all makes sense when explained, just sometimes i see this stuff and think wtf without really thinking it through. ;)
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