Direction of current through circuit breaker?

Question

I use products such as the Automotive-Standard Circuit breakers from http://www.waytekwire.com/index.htm. On the circuit breaker there is a label stamped on either side of the breaker. It is stamped BAT and AUX. My question is why does it matter which dirction current flows through a thermal circuit breaker?

Rich Z, your explaination sounded great so I decided to open up one of the breakers and take a peak. I was kinda shocked and little disapointed. The design is simply a very thin piece of what appears to be a flat, bi-metalic strip that is dimpled in two places to give it a kinda over-center snap when it warms up. The strip is rivetted to one stud and lays across another. No other components. Period.

Answer 1

DC circuit breakers often have additional features in them designed to quench an arc if there is a major current flow that they need to interrupt.

AC ones have it easier since the voltage through them goes down to zero during a cycle (which is why they can fail when used for DC which stays up). DC usage needs to put in other gimmicks [like magnets or a capacitor that creates a reverse current or a bypass transistor that drops the current after a delay] to suppress the arcing on a fault. Your breakers must have an active arc quenching technique that is polarity dependent.

Answer 2

"On a whim I reset the main breaker (which visually appeared to be in the on position) ..." Uh oh. You have a two-pole breaker, which means if an excessive current flows in the circuit of one pole, the overload trip mechanism will cause both poles to open and disconnect both circuits. But only one circuit got disconnected. This means 1) there is too much friction in the mechanism and the second pole could not trip 2) one of the poles has a defective mechanism 3) the main breaker is actually two independent breakers that are connected by a rod through the handles === #1 and #2 You need to get an electrician out to examine your breakers. It's possible the breaker needs to be replaced. You are in an old house. If the breaker is old, it's time to replace it. If the breaker is made by Federal Pacific, this could be a problem. Several years ago there were problems with Federal Pacific breakers and the breakers did not trip on overloads, and fires and damage to wiring resulted. If you use Yahoo! Search with the phrase Federal Pacific problem You will find several articles written in angry language about problems people and electricians had with some breakers made by that company. #3 If your main breaker is actually two poles ganged together, this is a dangerous situation. Current code does not allow this, as the combination is not guaranteed to have the mechanical integrity to trip both poles if only one circuit is overloaded. This breaker has to be replaced.

Answer 3

The design of the breaker will have some parts grounded so you have to have the source correct so you don't get electrocuted, but working wise it doesn't matter which way the current flows.