Hi,

I've been finishing my basement and I added a few 15A breakers
One room has 8 outlets in series with the first starting about 6 feet from the main panel. There is currently no load on this outlets.

When installing the drywall I accidentally shorted the outlet closest to the panel. It tripped the breaker, but it also tripped the main breaker. The wiring is 14/2.

I don't think this is normal. Is the breaker bad? Are there other things I should look for?

It does sound like your 15a breaker is bad or wired improperly. Shut off the main and check the 15a for continuity both open and closed. I usually don't mess with a breaker that may be bad, replacement is not very expensive so I go that route.

It sounds to me like the new breaker didn't do its job, but the main did. Wonder if you got ahold of a bad batch? I would wait and see what tkrussel has to say.

I am glad people now have him for these tough questions.

No, most likely neither breaker is defective. What you saw was the effect of what is called "AIC" or Available Interrupting Current, and low impedance of the circuitry and the grounding. Other than the nusinance tripping of the Main, all of this is a good thing.

Having a dead short so close to a panel results in the low impedance (AC resistance),causing the short circuit current to rise very high very quickly, which was above the threshold of the Main to cause it to trip in additon to the branch circuit breaker.

This is normal is those rare situations where several factors are "just right" so to speak.

I would not worry about anything at the moment, however, if the Main does trip too easily in the future, it may be an indication of being weakened, and will need to be replaced.

If for some reason you are not comfortable with my explanation or the condition of the main breaker, may be worth replacing anyway for the $40.00 and peace of mind.

Thanks for the advice.

The house is new so the main breaker should be in good condition, but it tripping just got me a little worried. When this happened I double checked the connections in the main panel and even tried swapping breakers (I bought 2) and both had tripped the main (and theirs) from shorting the first outlet.

Should I try to trip the breaker from farther down the circuit, e.g.. The last connect outlet? I did not want to do this more as I read that it is not good for the wiring.

First of all I have to assume the short is now cleared and the damaged cable has been replaced.

No need to test the breakers by intentionally shorting anything. Leave well enough alone, being new makes me feel better.

I did not get into a complete explanation of AIC rating, this is fairly complex topic not for this forum, but part of the cause of the main tripping, again nothing to worry about.

If you like to do more research do a Google search for AIC, fault current, short circuit current, there are other terms that all mean the same thing, but this enough to get started.

I have seen shorts, Very solid and direct trip 2 breakers, Replace if you have the money, it's probably OK. Worse I have seen by not replacing, is lower amp trip.
I would tighten every Breaker, Lug, Neutral and Ground. Especially Main Breaker.
Any further problem, change Main. 15 may be OK.
If replacing will make you sleep better, Small price for sleep.