in NJ I installed a sub panel and it was definitely wrong to have a main breaker in it. The main breaker is the breaker in the main panel that is feeding the subpanel. Its redundant anyway if you think about it. The sub panel had a groung and a nuetral that BOTH go to the main panel ground.

I think your first call should be to your local building department. They're the final authority as to what is acceptable and what is not.

Who installed this sub-panel? Was it inspected? If so, that should cover you.

Using a load center equiped with a main breaker for a sub-panel is done all the time and there is nothing wrong with it per se. The "main breaker" in the sub-panel becomes nothing more (or less) than a local disconnect for the sub-panel.

My hunch is that either (1) the 'GC' (who, btw, is probably not a qualified expert for the purposes of court testimony on electrical matters) doesn't know what s/he is talking about or (2) the alleged code violation is something other than what you've described.

Off the top of my head, here are a couple of possibilities you might want to consider:

The local sub-panel disconnect (i.e., second "main breaker") does nothing to protect the feeder wires from the main panel to the subpanel. Thus, if you wired the feeders from the main panel lugs (as opposed to a properly sized breaker), the feeders are exposed to the total current of the main service and may be undersized.

For example, assume the house has 200A service and you wired a 100A subpanel using #2AWG wire connected to the main lugs. While #2AWG is adequate for the 100A subpanel, it is not adequate for the 200A supplied to the main lug and this would be a code violation.

What size feeder conducters were used and are they properly protected by a breaker in the main panel? Assuming that they're connected to a breaker, it is THAT breaker that is the important overcurrent device and the primary disconnect for the sub-panel.

Secondly, it's possible that you interpreted the fact that the sub-panel had a "main breaker" and was marked suitable for use as service equipment" as meaning that it should be wired like a main panel -- specifically that the neutrals and grounds can be co-mingled as is legal in a main panel. Does the sub-panel have a ground bar and are the neutrals and equipment grounds kept isolated? If not, then you have a code violation.

Finally, it's possible that the "GC" is the one doing the misinterpreting. That is, perhaps s/he decided (incorrectly) that since it was a "main panel" the neutrals and grounds should be bonded.

Who knows? You need more facts.

"in NJ I installed a sub panel and it was definitely wrong to have a main breaker in it."

They must have changed the local code since the NEC does not prohibit a main disconnect in a sub-panel.

It is not required, but does make working tin the box at least a little safer.

You can turn off the 'main' in the panel and know that the breaker lugs are no longer hot.

Only the panel feed and the source side of the 'main' remain hot.

A main breaker in a subpanel is POINTLESS unless it is smaller than the feeder breaker. if it is the same size or larger then it decomes a ''line of sight disconnect'' (joke)

A larger main breaker in a sub-panel may be pointless, but it is frequently cheaper to use it than a panel without. Like HALF the cost sometimes. Supply and demand I guess. Kind of like spa- paks vs. Tandem GFI breakers.

OJ has it right. Often you can get package deals in one carton, with a main panel and several breakers, for less than you'd pay for a main lugs panel alone. I guess it's because they're produced in large quantities for builders and the competition is strong.

A main breaker in a sub is no big deal aye or nay, if the sub is right next to the main panel. But if it's on the other side of the house, or on a different floor, that local disconnect is nice to have.