Main breaker or electric cabinet too sensitive?

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kylelee

kylelee

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I've encountered a very bad situation today when I was working in a small apartment unit, a bx wire 14/2 was not capped well and lose touched a metal stub, cause this building main breaker tripped ,( the 15A breaker did trip ,but even the 50A unit main breaker not trip), half of the building was down.this was too bad, Omg was I bad luck ?


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Ground fault detecting main, set to minimum trip levels.

Apparently does not coordinate well with basic thermal/magnetic branch circuit breakers. Lots of stories of these sort of problems described on this forum.

-Jon
 
winnie said:
Ground fault detecting main, set to minimum trip levels.

Apparently does not coordinate well with basic thermal/magnetic branch circuit breakers. Lots of stories of these sort of problems described on this forum.

-Jon
Click to expand...

So it should be time delay?


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kylelee said:
So it should be time delay?


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Click to expand...

Thermal trip is what is has a delay response.

Magnetic trip should be nearly instantaeous, magnetic trip is often adjustable on larger breakers, this one was likely left on minimum setting when installed.

Or as mentioned it could have ground fault detection and is set too low.
 
You can see it in the photo, lower left corner. There is a graphic that looks something like a trip curve, with little windows. The labels are 'short delay pickup' 'short delay time' 'gnd fault pickup' and 'gnd fault time'. (Can barely be made out in the photo, but a google search for 'cutler hammer 310 trip unit' will find a manual.)

This breaker can be set for different pickup levels and different pickup times, with separate settings for overload and for ground fault.

You can't really trust an internet discussion forum to tell you what the proper settings should be; get someone who is trained in breaker coordination, do a study, and get the correct values set.

-Jon
 
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