3 phase grounding

Residential service panels must be bonded to ground and distribution panels must be bonded to the grounding bus. What about panel bonding regard 3 phase power?

What are some other 3 phase specific items to look for?

Can I make the assumption that you are talking about bonding the neutral and not bonding the panels and raceways?

The neutral should be bonded within the transformer, coming off the Xo tap and connected to the case of the transformer. Although, I highly doubt you’ll be taking off the tranny covers to look.


You may find commerical / industrial 3-phase systems grounded in several ways - low rersistance (or solid), high-resistance, and in some older systems, completely ungrounded. It really depends on the protection system employed. All of the panels, cabinets, etc. are generally bonded to a well-designed grounding system. There are greatly varying opinions as to how 3 phase systems are best grounded, with many papers having been written and presented on the subject.