100 Amp main trip

[H.L.]

#1 I am trouble shooting a 240/120 panel in a parking structure. This panel feeds HID lighting. The top half of the panel is always on The bottom is fed through a contactor that intercepts the buss. The contactor is operated by a timeclock. The main breaker is an ITE ED43B100 w/ an accessory ground fault relay. The main would trip frequently (1-3 days). I disconnected the G.F. relay and the main has not tripped since, that was about 2 weeks ago. Is there a way to test the relay to see if it is working properly?

#2 On the above install all three phase conductors and the neutral go through the doughnut. How does this sense current? Shouldn't all the phase currents cancel each other?

Hale

 

[barbeer]

Rather than assume a component is bad I would start with a ballast is going bad.(shorting) The relay may be bad but a shorting ballast or conductor is more likely.

As far as the donut...I am really not sure but believe it to be a current transformer and work via induction, like you I would believe that each phase should be separated.

 

[coulter]

... On the above install all three phase conductors and the neutral go through the doughnut. How does this sense current? Shouldn't all the phase currents cancel each other?...

If all of the current that leaves by the phase conductors returns either through another phase conductor or the neutral conductor then as you said,
Summation (I) = 0

If there is a ground fault, then current is returning by another path and does not go through the donut. So:
Summation (I) <=> 0, and the CT will show the current imbalance.

Having all four conductors going through the one window is far more sensitive to low level ground faults than having each conductor through it's own CT.

carl

 

[H.L.]

Re: Shortting ballast
I do not believe that a ballast is the problem as all fixtures are individually fused. I could meg all the ckts but I would have to disconnect each fixture. It may come to that.

Carl,

Thanks for your explanation. Now I got it!

Would the CT see a leakage in the transformer that feeds the panel?

H.L.

 

[Pierre C Belarge]

It would seem by your explanation that you may have a low level ground fault or maybe some leakage current that has developed in the conductors causing the GFP to trip the circuit.

If you do not find the problem in the fixtures, maybe you will need to megger the conductors.

Just a thought...

 

[coulter]

...Would the CT see a leakage in the transformer that feeds the panel?...

No , the CT will only see leakage that occurs after the CT.

...I do not believe that a ballast is the problem as all fixtures are individually fused. ...

Why not? There could easily be enough of a fault to trip the GPE and still be well below the fuse rating. The GPE is there for exactly that reason - to catch the low level faults that don't draw enough to open the fuse.

...I could meg all the ckts but I would have to disconnect each fixture. ...

Well, all of the responders are sending the same message: Believe your instrumentation. It's telling you there is a low level fault. My recomendation is the same as theirs - Go look for it.

carl