Feeder Ground for Subpanel Loose in main Panel

This is new construction. The 100 amp feeder for the subpanel is 4 wires and the ground is loose in the main panel but all 4 wires in the subpanel are connected. So far so good, ask the builder fix it right? Well…Yes, but I also noticed that all of the outlets in the house showed normal wiring with a regular 3 prong tester. Shouldn’t the tester show open ground???

Am I missing something? It should be open ground unless somehow there is another unknown neutral to ground connection somewhere right? That’s what’s got me stumped.

Is it likely that the bare EGC in the sub-panel feeder is contacting bare metal (bare EGC, neutral bar, etc.) in the service panel?

It might be making enough contact with the bus in the service panel?

Yes, I think the feeder ground touching the EGCs for the larger appliances in the main electrical panel makes the most sense. Otherwise the feeder ground wasn’t touching the bus bar and the paint on the panel box is not stripped or anything. Panel had some water at the bottom from the pressure washer guy just hosing down the whole wall, so I was kind of thinking the water had something to do with it.

Still, with such a weak connection, I’m surprised the lights on the 3-prong tester were so solid. I’ve had outlets with a slightly loose ground show a dim or slightly flickering light on the 3-prong tester and then I go back and check it with the ideal sure test and it shows full open ground. Open up the outlet, tighten the ground screw and then both read normal.

Thanks for the help!

Depending on how much pressure was holding the one conductor against the other it may have been enough to fool the tester. If you put a ground fault directly on the the receptacle EGC it would probably burn the connection point between the two conductors.