Lighting contactor

T

Therealcrt

Senior Member
Location
Kansas City
Occupation
Electrician
tell me why this keeps happening

I’m doing some troubleshooting on some parking lot pole lights there are two circuits sharing one neutral going out from the contactor cabinet to the pole light. I disconnected all of the incoming wires to the pole, separating everything when I turn the circuits on and cover the photocell to close the contactor. It blows the contactor and keeps the contactor in a stuck closed position. I’ve replaced two contractors now there is no continuity between any hot and ground or any hot and neutral or any hot and hot when I have one circuit on it holds the breaker, but when both circuits are on it trips, both breakers Again there is no load connected no indicator of a short or fault it’s 277 V to add And the contactor is a three pole 30 amp 277 V coil contactor. The breakers are single pole 20 amp breakers.
 
Was it working fine for a while and then started acting up, or was this from day 1?
I assume you metered out the voltages on the incoming feed and it all was dandy.
I guess a picture of how it's wired up could help.

So if you disconnect all loads, then turn 1 of the remote circuit breakers on it's fine, but turn the second breaker on it blows? Did you swap which breaker you turned on first (guess that's a pricey test)?

What is the coil rated for and what's feeding the photocell switch? Is the photocell at 277 (or 120 or whatever) when both circuits are live?

Perhaps miswired and the holding coil is getting 480V when both legs are hot and it's only rated for 277, or somehow the coil rating is out of step with what it's receiving, not sure... Someone here already has it figured out probably.
 
1 photocell is powering 5 contractors the voltage is all 277 and the coils are 277 rated. Yes I’ve used different breakers also. It Instantly arch’s at the contactor and gets stuck closed
 
Therealcrt said:
1 photocell is powering 5 contractors the voltage is all 277 and the coils are 277 rated. Yes I’ve used different breakers also. It Instantly arch’s at the contactor and gets stuck closed
Click to expand...
Is it always the same one of the 5 that fails?
If it immediately arcs you have some type of short circuit in the control circuit.
Do you bench test the contactor before installing it?
 
NoahsArc said:
Was it working fine for a while and then started acting up, or was this from day 1?
I assume you metered out the voltages on the incoming feed and it all was dandy.
I guess a picture of how it's wired up could help.

So if you disconnect all loads, then turn 1 of the remote circuit breakers on it's fine, but turn the second breaker on it blows? Did you swap which breaker you turned on first (guess that's a pricey test)?

What is the coil rated for and what's feeding the photocell switch? Is the photocell at 277 (or 120 or whatever) when both circuits are live?

Perhaps miswired and the holding coil is getting 480V when both legs are hot and it's only rated for 277, or somehow the coil rating is out of step with what it's receiving, not sure... Someone here already has it figured out probably.
Click to expand...
It started acting up one day
 
Therealcrt said:
there are two circuits sharing one neutral
Click to expand...
As in a MWBC? Did you confirm that the "two circuits" are on different phases? That's the only way "two circuits" can share one neutral, right? Unless I'm missing something else here, please educate, thanks.
 
jim dungar said:
if you have (1) photocell feeding (5) parallel contactor coils and one random coil fails, there is a wiring problem in the control circuit.
Click to expand...
But there isn’t. Not the same (1) keeps failing. I also put those circuits on different contactors and it did the same to those contactors too..
 
Therealcrt said:
But there isn’t. Not the same (1) keeps failing. I also put those circuits on different contactors and it did the same to those contactors too..
Click to expand...
The coils should have nothing to do with the load circuits.
Is this one contactor per photo cell? Post #3 sounds like coils in parallel.
 
Are you sure the PC can handle five contactors' worth of coil current?

Added: Are the contactors remaining energized or physically stuck?
 
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