I have the following:
- a NEMA 5-20 receptable (typical 20amp grounded receptacle) mounted in an exposed work cover on a metal box fed with 12ga conductors through EMF.
- a typical string of holiday lights with a non-polarized plug.
I accidentally misaligned the plug while trying to insert it into the receptacle. One blade entered the ungrounded conductor ("hot") slot of the receptacle, and the other pressed against the metal exposed work cover.
The lights lit, and the 20 amp breaker did not trip. Should it have?
My present understanding is that since everything was still going through the lights (i.e., there was no fault to ground, but only this connection through the resistance provided by the string of lights), and since the breaker is simple overcurrent protection (it's not a GFCI or AFCI breaker), the breaker should not have tripped.
However, if it were a GFCI breaker, then because current returned through the equipment grounding conductor ("ground") rather than the grounded conductor ("neutral"), the imbalance between hot and neutral would cause a trip. (And because the ad hoc connection was pretty loose, there could have been arcs, which would have tripped an AFCI.)
Is my understanding correct and I just need to exercise more care when plugging things in, or do I have a wiring situation that needs to be fixed?
There have been some comments about whether the box has a cover, and whether this requires bending the plug blades, and the like. It doesn't, as illustrated in this picture (taken with the breaker off):