breaker trip on ground fault

Status
Not open for further replies.
S

snjeza

Member
Hi,

In the power plant the elevator controls were replaced. With the old control they never had an equipment grounding conductor run in the raceway from the load center to the elevator motor. They have ground grid in the plant and each peace of equipment is grounded to the grid. Now, with new control they connected equipment grounding conductor between an elevator control cabinet and the fused disconnect switch in the elevator room and they tripped circuit breaker in the load center (in the basement). Breaker tripped on ground fault (breaker has solid state trip unit GE). Elevator control cabinet, elevator motor and disconect switch were connected to the ground grid at both cases.

This is happening on two different elevators.

I will appreciate any ideas about what is going on here.

Thank you.
 
Is this a 3 phase 3 wire circuit to the elevator, no neutral?

Exactly when does it trip? When you close the disconnect with the elevator stopped? Only when the elevator moves? Does it trip with the disconnect open (off)?

Is this a feeder breaker tripping or the main in the panel?

And more out of curiosity, what is the CB trip and time delay set at?
 
Last edited:
3 phase, 3 wire system with no neutral. Load center is fed from delta-star solidly grounded transformer. Neutral was not needed since all loads are 3 ph, 3w.
I'm not sure when exactly the breaker tripped. They told me it was not immediately after the circuit was closed.
It does trip only elevator feeder breaker.
Breaker has GE solid state trip unit 225A.
Instantenious is not set.
Short time delay is set at 8.
Long time delay is set at 1.
Ground fault is set at 0.6
 
There are some values missing from your setting info but that's OK. You should have settings for long time delay, short time pickup, short time delay, ground fault pickup and ground fault delay, and rating plug amps.

Most GF problems are due to incorrect neutral wiring downstream but that's not an issue here. You should investigate if it is tripping when the elevator is running or not. The only comment I have is I don't know why such a small CB was specified with ground fault trip. Check with local codes but I'd imagine you could turn it off and let the phase trip elements deal with any ground faults. Setting a GF trip at 135 amps seems way too conservative to me. Just my 0.02
 
snjeza

snjeza

Sensor rating is 300A and tap at 225A.
Long time 47sec
Short time 0.15sec
Ground fault delay 0.15sec

I will find out when it was tripping. I still don't know why is it tripping. Everything seems to be wired properly.

Thank you.
 
Status
Not open for further replies.
Top