Does it matter if the load side is connected at the top or at the bottom terminals of a circuit breaker? What are the impacts, if any, on the correct operation of the circuit breaker?

 

Excellent question...

In most cases bi-directional current-flow, such as a tie-breaker in a secondary-selective configuration, is acceptable. But, this condition must be clearly specified to the manufacturer to include an assessment of what happens wnen the breaker is called upon to interrupt fault-current flowing in either direction, i.e., top to bottom and reverse, as well as the propagation of the ensuing arc and arcing products. It must never be taken for granted!

BTW, this is a good thread to bring up another potential design error... the danger involving breakers mounted on withdrawable-frames. I investigated several incidents where a ground-fault occured inside the withdrawable-frame. The ground fault-fault return path included a brush contact in parallel with metal wheels rolling in channel iron. Both were wholly inadequate resulting in catastrophe. Both sides of secondary-selective switchgear lineup, 15-20 mt in length, was obliterated in less than two seconds.

A third Caveat involves encasement of the tie-breaker, to insure an arc, and its products can't transition across the compartment!

If anyone is interested in seeing photos of how much damage 50kA of current can do in 2 seconds contact me off-list.

Regards, Phil Corso (cepsicon [at] aol.com)

 

For Rob, re your request for photos...

I received message that my reply to you was "undeliverable!" Do you have a 2nd email address?

Phil