My subpanel has neutral and ground all mixed together?

Question

I read that this might be bad, but it appears both neutral and grounds are mixed on two different bus bars. It isn't just one wire that doesn't follow the pattern; there are several neutral wires on the predominantly ground bus bar. Should I rewire everything to separate ground from neutral? The subpanel is in my garage -- it's largely for pool equipment. It's 60A and runs from the main house underground from the primary 200A service panel. This wouldn't be the first crazy thing I discovered from the previous homeowner (eg, shelves sitting on top of upside down square brackets).

Also, would this be a reason for a GFCI breaker to be tripping instantly in the subpanel?

Thanks!

Answer 1

Four Wire Feeder

If the panel is supplied by a four wire feeder (hot, hot, neutral, ground), then yes, the ground and neutral should be separate in the second panel.

If the panel is GFCI protected, and fed by a four wire feeder. Mixing the neutrals and grounds in the panel, will almost certainly cause the GFCI to trip. By mixing grounds and neutrals, you've essentially bonded the grounding and neutral bus bars together. This causes neutral current to be split between the grounding and neutral conductors of the feeder. Which means that the GFCI device will not see enough current on the neutral, and will open the circuit.

Three Wire Feeder

If this is an older installation, where the panel is fed by a three wire feeder (hot, hot, neutral), then the neutral bus bar should be bonded to the ground bus bar. In this case, mixing grounds and neutrals is poor aesthetics, but not a code violation.

If the panel is GFCI protected, and fed by a three wire feeder. Mixing grounds and neutrals should not trip the GFCI.

Answer 2

Yes, in the sub panel ground and neutral should be kept separate.

Answer 3

The subpanel ground and neutral do need to be kept separate -- neutral is the return path, ground is a safety-drain if you will that is not meant to be energized in the normal case. (In the hydraulic analogy, neutral is the drainpipe coming out of the machine and ground is the floor drain under the machine in case it leaks.)

This confusion would also explain why your GFCI is tripping -- the GFCI is seeing current out that's not coming back in through it, as it's being diverted through the grounding network instead.

(P.S. be glad your subpanel hasn't developed an open neutral, as the current cross-connection would yield quite shocking results if that happened.)