In a local mall a contractor is doing demolision, they cut into a 277 volt lighting circuit, the 20 amp branch breaker tripped in the stores panel and also a 400 amp main breaker tripped in the Malls main switch gear. trying to find out why.
Not that unusual, does the 400 amp breaker have Ground fault settings?
What is a selective coordination calculation.The short circuit current did not only flow through the 20 amp branch circuit breaker. It also flowed through the branch circuit panel?s main breaker (if there is one), through the feeder breaker upstream of the branch circuit panel, through the main breaker of the upstream panel, and through any and all other breakers that lie between the service point and the fault point. Why would you suppose that any one of them would trip before any other one? They all saw a current level much higher than their normal current ratings. The 400 amp main breaker saw a current much higher than 400 amps, so why should it not trip?
If you want to force the upstream breakers to delay their tripping, so as to give the breaker closest to the fault a chance to trip first, thus limiting the power outage to a small portion of the distribution system, then you need to have a ?selective coordination? calculation performed. Then you will probably need to replace some of the breakers, bases on the results of that calculation.
Welcome to the forum.
That's a fairly long document. But you can get the essential concept from just reading page 4 of 53.Below is a link to some detailed information on selective coordination.
Thanks I'll check it out.Below is a link to some detailed information on selective coordination.
http://spd.cooperbussmann.com/Documents/SPD_Sec5.pdf
But the unexplainable tripping of the main device for the store isn't?A selective study is very expensive BTW....
Somehow, that's the concept that a lot of people fail to grasp unfortunately, especially bean counters who are focussed on immediate bottom line costs for a project.But the unexplainable tripping of the main device for the store isn't?
Somehow, that's the concept that a lot of people fail to grasp unfortunately, especially bean counters who are focussed on immediate bottom line costs for a project.
Somehow, that's the concept that a lot of people fail to grasp unfortunately, especially bean counters who are focussed on immediate bottom line costs for a project.
One possible reason is that there are overlapping areas when you compare the trip curves of both breakers. Most likely you'll find this area on the graphs at current levels of substantially more than 400A.In a local mall a contractor is doing demolision, they cut into a 277 volt lighting circuit, the 20 amp branch breaker tripped in the stores panel and also a 400 amp main breaker tripped in the Malls main switch gear. trying to find out why.
A selective study is very expensive BTW....
A selective study is very expensive BTW....
But the unexplainable tripping of the main device for the store isn't?