Confused! I have searched this forum and past post for awhile and the more I read the more I get confused. I have seen a few diagrams showing grounding/bonding of a three wire feed and a four wire feed to a separate structure fed from the service panel in the house. I see that both systems would require their own grounding electrode per 250.32. I understand that in the four wire system, the grounding bus and the neutral bus must be isolated at the sub panel in the detached structure, regardless if the feeder conductors are in metallic or non metallic conduit. I guess my confusion is with a three wire system, the diagram is saw posted shows that the neutral bus and ground bus are bonded together in the sub panel and that no other metallic paths are allowed between the two structures, in other words the feeder conductors must not be placed in metallic conduit. Can some one please try to explain this to me as simply as possible? THnaks
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- Thread starter VIC1958
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- New Jersey
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- Journeyman Electrician
Three wire feeders were removed from the NEC in 2008. Now they are permitted in existing installations only. If you had only a 3-wire feeder you would need to bond the neutral to establish an equipment grounding system at the detached structure. If you had a metallic raceway then that could be used for the EGC and you would technically have a 4 "wire" system.
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