When to Bond Neutral to Ground in Electrical Panels - E&S Grounding

John asked:
Should you make neutral-to-ground bonds in electrical panels?

Our Answer:

• If your electrical panel is a subpanel, then NO, you do not make a neutral-to-ground connection.
• If your electrical panel is the first service disconnect point, AND the utility has only provided normally current carrying conductors (phase and neutral wires), then YES, you must make a neutral-to-ground connection.
• If your electrical panel is the first service disconnect point, and the utility has only provided normally current carrying conductors (phase and neutral wires) PLUS a ground wire, then NO, you do not make a neutral-to-ground connection.

Please see NEC Article 250.28 for when to make a neutral-to-ground connection.

Please see NEC Articles 250.6(B), 250.24(A)(5) HB Notes, 250.30(A)(1) Exception #2, 250.30(A)(5) HB notes, 250.32(B)(1) HB notes, 250.142(B), and HB Exhibit 250.8 for information when NOT to make a neutral-to-ground connection.

What About 5-wire Electrical Systems?

If you have a 5-wire system from the transformer (3 phase wires, neutral and ground), you should NOT have a neutral-to-ground bond in the service (just like in any other transformer to panel scenario). In fact, a 5-wire feed from the transformer is the BEST and safest electrical system possible.

The neutral-to-ground bond was in fact invented to save money so that a grounding wire did not have to be run from the transformer to the first panel. The IEC does a much better job making this clear while the NEC is terrible at it.

Consider the following scenario: a wall inside a building with two electrical panels. The first panel is 480V which feeds a floor mounted transformer, which in turn feeds the second panel which is 208V. The panels feed 5-wire to and from the transformer. Where would the neutral-to-ground bonds go?

Here is the list of codes for why we recommend removal of neutral-to-ground bonds in 5-wire electrical systems:

NEC Rules:

• NEC 250.24(A)(5) see Handbook notes
• NEC 250.30(A)(1) Exception #2
• NEC 250.30(A)(5) Handbook notes
• NEC 250.32(B)(1) Handbook notes
• NEC 250.142(B)
• See Exhibit 250.8 in the Handbook where the connection can be at the load end of the service drop

CEC Rules:

• Rule 10-200(1) states that objectionable currents must not flow through the grounding system during normal operations.
• Rule 10-204(1) states that neutral currents must not flow on the grounding system back to the transformer.
• Rule 10-204(1)(c) states that you are not to make connections at the consumers service that will cause neutral currents to flow on the grounding system.
• Rule 10-200(3) gives us recommendations for removing objectionable currents from the grounding system, including the removal of neutral-to-ground bonds in the cabinet.

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