What could cause sudden failure of outlets?

Question

Suddenly some of the outlets supplying our table lamps quit working. I checked the breaker and it wasn't tripped, but I reset it anyway. Still no power to some of the outlets. So I turned off the power and pulled out the outlets. Tested for continuity and found there was no continuity between the operational outlet and the dead one. What could cause this?

Answer 1

Sharing knowledge--answering my own question:

Rodent damage is not often discussed here but it's real. Fortunately the outlets on the wall that failed were on a shared wall with the attached garage. I opened up the wall on the garage side and found this little guy, electrocuted in place. He'd chewed thru the cable, broke the hot or neutral wire, kept going until he "made contact". So when you experience a weird failure that can't be attributed to a tripped breaker, tripped gfci, loose connections on switches or outlets (particularly the notorious back-stab outlets), it could very well be rodents such as mice, rats, squirrels, etc.
Based on some comments, I'll edit my own answer:

To fix it I simply ran a new cable between the two outlets, no splicing involved. Fortunately it was an easy and accessible path to do that. And YES!...SPEC GRADE outlets, no back-stabs, like Harp says. In fact, I believe I replaced most of the outlets in that home with spec grade, but that was 20 years ago, so not sure. In my new home, I wired all convenience outlets with 12ga, 20amp spec grade outlets. That's how you do it!

Answer 2

You've already answered, but I'll throw in another suggestion: a GFI outlet in the circuit.

GFI (or "GFCI") receptacles sold in the USA typically come with an "upper" and a "lower" set of screws, where the "lower" set has a bit of yellow tape across them:

The reason for the yellow tape is to avoid confusion with a "feature" of GFI receptacles: they are capable of protecting non-GFI outlets located downstream on the same circuit.

If you wire a GFI receptacle into a circuit using only the "top" screws (those not covered by tape) then the GFI protection only applies to appliances plugged directly in to that outlet. But if you wire the circuit so that the "line" connects to the top screws, and other outlets connect to the "bottom" screws (after removing the tape!) then those other outlets will be protected by this GFI receptacle.

As a result, if you have a plain vanilla outlet that stops working, one possible reason might be that it is protected by a GFI receptacle somewhere else in the circuit, and that GFI has tripped.

Answer 3

You didn't talk about the screws being tight, so my guess is these were wired with backstabs.

Backstabs are notoriously unreliable. As you may notice, it is optically impossible to physically inspect a backstab connection.

You can twist the wires out of the backstab, strip them to the proper length, and attach them properly to the side screw-- which mind you is a fairly tricky maneuver, and you should watch some Youtube videos on how to do it properly.

Or, you can change the receptacles to the $3 "spec grade" receptacle, which has a back-wire system where you must tighten the screw down to clamp the wires. Those are reliable and there's no need to learn complex technique. But crank down seriously (ideally: to stated torque spec).