Breaker trip?

A few days ago I plugged in my little pancake compressor and it wouldn't start. As I was looking down at the compressor, not touching it, I heard a whoosh and saw a long flame shooting out of the plug that was in the socket. I quickly grabbed the wire and yanked it out of the socket. I immediately thought that the previous owner must have had a habit of yanking on that chord as I had bought this pancake compressor at an auction a few years ago.
I have replaced the plug and the burnt wires, however, I am wondering why the breaker did NOT trip? Usually a short would trip the breaker.

I'd start by finding out how large the breaker is. Maybe its to large for the circuit. If someone had problems with tripping the breaker in the past that could have been their fix.

A flash or arc is not necessarily an over load or short enough to cause a breaker to trip. Thats why they always blame faulty wiring on
fires.

Possibly instead of a short, it had a really poor connection. Pulling on the cord finished it off.

Did you repair the cord? And did that make the compressor run?

I wouldn't worry too much about the breaker. About the only thing you could do would be to intentionally short it (not recommending it), or replace it as a safety measure.

The breaker only protects the wire to the outlet. If the cord on the compressor is rated for a lower amperage it could easily burn up without tripping the breaker. Had it continued for much longer I think the breaker would have heated up enough to trip.

What brand ? I'm guessing GE

If it would of been an AFCI (arc-fault circuit interrupter) it should of tripped, otherwise like others have said it probably wasn't overloaded, and not for a long enough time. You can plug in a couple of electric heaters to overload the breaker and trip it. I was working on a construction job once when the electricians were testing the breakers, he showed me a bad one. He had a horseshoe shaped piece of wire in his pliers, shoved it into the receptacle, and it just hummed! And it was a Square D!

What was the air temperature?

I have a small conventional compressor in the garage at my house, and sometimes if the temp is in the teens or below the oil will be stiff enough that it will trip the breaker if I try to start it.

Thinking about it, though, I'd suspect a faulty plug on the compressor before I went any farther.

The breaker could be bad even if the cord needed to be repaired. If a breaker has been used repeatedly as a switch for the circuit, they do wear out. Make sure the breaker is not a slow blow type, typically
used to protect a circuit with high peak starting loads.

I've done that, intentionally short a circuit to find the breaker.

Learned a hard lesson though...

Shorted one, it killed the circuit, but didn't trip the breaker!

Searched for hours blindly tracking the wiring, pulling out receptacles thinking it blew the wire loose, nope, could not find it! Finally after 2 days of frustration found a spliced wire (illegally) closed up inside the drywall!

Turned a 30 minute job into a 3 day ordeal!

If the short was high enough resistance it may not drawn enough amps to trip the breaker.

Doug, great QUESTION

however, I am wondering why the breaker did NOT trip? Usually a short would trip the breaker.

ANSWER

The breaker (assuming it was good) DID NOT SENSE ENOUGH CURRENT to trip even if you saw fire and arcing and smoke.

It doesn't take much current (even far less than the 15 or 20 amp breaker) to arc n spark and just because you see that DOES NOT MEAN the
breaker senses 15 or 20 amps which is enough to trip.

What you experienced is one reason why the NEC started specifying ARC FAULT PROTECTION because its easy and quite possible a high heat and
flame arc can start a fire even though there's NOT enough current to trip a 15 or 20 amp circuit breaker. A short may be too high
resistance to allow 15 or 20 amps of current flow to trip a circuit breaker even if there may be big time arcing n sparking YIKES

..........If the compressor happens to be a Capacitor Start and its bad that can contribute to starting problems

..........If theres a loose or burned or carboned resistive connection (or bad plug or receptacle) that can develop extreme heat and
sparks and arcs

.......... Check the start capacitor and especially its wiring connections IF IT HAS ONE

......... Replace/repair the plug and any receptacles with problems

......... If in doubt REPLACE THE CIRCUIT BREAKER JUST TO BE SAFE as they can fail especially if old and/or suffered too many trips

.......... There may be problems with the ampacity of the branch circuit being inadequate to start and run the compressor

........... There are all kinds of rules and exceptions regarding motors and circuits and overload protection and HACR Breakers and dual
action time delay fuses etc etc but Im NOT going into that for now lol as it was NOT part of your question


John T NO WARRANTY Im too long retired from power distribution so where fire and life safety are concerned, DONT TAKE MY WORD FOR IT,
consult trained professional electricians and engineers and the NEC, the risk is too great

x2 uninformed call it a short.
Sometimes the uninformed call it a short when it's actually an
open too.
Opens don't blow breakers.
Good chance when smoke leaves, it produces an open.

Thanks for all of the replies.
I have repaired the plug and cord and the compressor works just fine. It has a 3/4 hp motor and it has no capacitor. The breaker is 15 amp and the pictures show the breaker (black) just after the flame out and also after a reset.


This is the reset position of the breaker. It looks to be seated slightly better on the reset.