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Old 1/25/19, 3:55 PM
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Robert Meier Robert Meier is offline
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Default Re: 3 vs 4 wire feed to garage

Originally Posted by jolson8 View Post
In a 3-wire sub(distribution) panel the grounds and neutral should not be separated?

Actually they cannot be. If you isolate the EGC and neutral there will be no return path for the current to open an OCPD and the system will be ungrounded.

If you think of it like a service the reason that a ground fault to an EGC trips the OCPD is because the EGC's and the neutral are bonded together. With a 3-wire feeder you would also have to bond the EGC to the neutral for a ground fault to open the OCPD. For separate structures this was permitted until it changed with the 2008 NEC.