Using an Ohm Meter to test for bonding of a subpanel

Question

I'm selling my home and the home inspector is saying my neutral bar is bonded to subpanel box. He is basing this on his ohm meter reading continuity between the neutral bar and the ground bar. There is no bonding between the neutral and the box. I have disconnected all the neutrals as well as the feeder from the neutral bar and tested between the neutral bar and the ground bar to infinity ohms. I reconnected all the neutrals except for the feeder and still have infinity ohms. How can an inspector ever expect to get infinity ohms with that type of test when the feeder neutral is connected? The feeder is bonded to the ground at the main service panel and there is a ground wire coming from the main service panel back to the subpanel which is connected to the ground bus which in turn is connected to the box. I'm a bit confused.

Answer 1

The panel looks beautiful, except for one problem.

You are 100% correct. Because neutral and ground are bonded in the main panel (whether that is a regular big panel or a small panel/disconnect at the meter), any check farther on in the system - subpanel, receptacle, etc. - should show very close to 0 Ohms, and low enough that a typical multimeter continuity test will beep.

It simply can't work any other way. And since neutral is not breakered, the only way to really verify this (beyond a visual check to make sure there is no bonding screw on the neutral bar and no grounds on the neutral bar) is to do what you already did:

• Disconnect the neutral feed
• Check for continuity between the neutral bar and the ground bar

This is, of course, trivial on a new installation. But on an existing house, barring troubleshooting an actual problem, there would be no reason to do this. And, in fact, this would not be advisable as the neutral feed wire (especially if the panel/feed is > 50A) is a big wire and not so easy to manage for non-professionals. And it has to be reconnected properly afterwards.

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And now for the problem...

You should have ~ 23 branch circuit neutrals - one for each single breaker and one for each double breaker, with the exception of a double-breaker circuit with no neutral (e.g., water heater, HVAC compressor, or some cooking appliances). You have ~ 13 neutral wires on the neutral bar. Plus you have the telltale alternating black/red branch circuit hot wires. Which indicates you likely have a whole bunch of Multi-Wire Branch Circuits (MWBC). Each pair of MWBC breakers must * be either a double-breaker or handle-tied. Since the breakers are already paid for, handle-ties are the cheaper way to go. Currently $6.83 for a 3-pack at Home Depot and likely less in bulk at an electrical supply house:

Handle ties (or double breakers) for MWBCs perform two critical functions:

• Make sure that if you turn off 1/2 of an MWBC for maintenance that the other half is also off so that you don't get zapped by shared neutral current.
• Make sure that if breakers are moved around that they stay in proper pairs. Otherwise they could switch from separate legs to the same leg and end up with double neutral current instead of net zero neutral current when fully loaded.

* As noted in a comment, handle ties only became a requirement with NEC 2008, which means in the 2010s for most states. So if the house is more than 10 years old then likely grandfathered. That being said, this is a simple, easy and inexpensive code-based improvement, unlike adding AFCI breakers or splitting circuits that are now required to be dedicated.