Unidentifiable serious problem

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dave h

Member
Location
Bergen, New York
Pole lighting on a soccer field.
We have 6 poles with a total of 27, 1500 MH floods running at 120 volts. The one conduit with 4 - 3 phase, 4 wire circuits circuit we are having a problem with controls 4 of the poles. The lighting is on 60 amp contactors, one for each pole. the four we are concerned with have 5,4,4,5 fixtures.

When its raining the person(s) turning the lights off are reporting a loud bang and a large flash of sparks coming from the breakers in the panelboard and the gutter below the panelboard. Outsde the building a cover blew off a gutter and bend the lid up 1.5 inches. The first time this happened was last fall, testing was done and faults were found in the feeds as well as there being no grounding in the building. Grounding was installed and all new feeders installed to the poles.
The system worked fine untill the first day of a soaking rain, the lights operated for 3 to 4 hours, then as they were being turned off the explosion repeated happened. We were back the next day and ran every test I could on wiring and gounding, no problems at all.
This never causes a breaker to open from short circuit. And I can't get it repeat the explosion when we are testing. Each fixture is also fused at the pole base with 20 amp cartrige fuses.

Any suggestions as to what he problem could be?

Please send any suggestion....Thanks dave h
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I do not believe grounding has anything to do with this.

The fact that it only happens when it has been raining is a major clue. perhaps water is getting on the contactors.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Disconnect all the underground wiring at each end and start testing with a mega meter.

Be prepared to be replacing a lot of wire.
 
cadpoint

cadpoint

Senior Member
Location
Durham, NC
Welp, maybe then you should have gone ahead and read the continuity between the circuit runs, since you had it all apart and the meggar didn't want to play.

I'm frankly surprised it didn't show something! Whats the contactor look and what does look it like in the panel or below?

Is the service in with the branch circuits in this trough?

Just a thought that the contactor are bleeding back or even crossing themselves when being released.

The contractor itself are toasting itself...
 
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dicklaxt

Senior Member
The operating current @120v on a 1500W Metal Halide is 13.5 amps,that times 5 is 67.5 amps just a shade overloaded don't you think? You may have a high current switching problem and water is getting in the fixtures somehow and adding to the problem.The fact that 1 of the phases is not evenly loaded coupled with the other problems is a problem in itself....doesn't look to kosher.

just a thought

dick
 
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dave h

Member
Location
Bergen, New York
dicklaxt said:
The operating current @120v on a 1500W Metal Halide is 13.5 amps,that times 5 is 67.5 amps just a shade overloaded don't you think? You may have a high current switching problem and water is getting in the fixtures somehow and adding to the problem.The fact that 1 of the phases is not evenly loaded coupled with the other problems is a problem in itself....doesn't look to kosher.

just a thought

dick
Click to expand...

Thanks, the actual load per leg would be 27, 27, 13.5. each bank of lights is fed with a 3 phase 4 wire circuit
 
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dave h

Member
Location
Bergen, New York
cadpoint said:
Welp, maybe then you should have gone ahead and read the continuity between the circuit runs, since you had it all apart and the meggar didn't want to play.

I'm frankly surprised it didn't show something! Whats the contactor look and what does look it like in the panel or below?

Is the service in with the branch circuits in this trough?

Just a thought that the contactor are bleeding back or even crossing themselves when being released.

The contractor itself are toasting itself...
Click to expand...

Continuity was read befor all final connections were made...all clean.
The contactors are new, 2=3 weeks.
Service conductors in a different gutter
Did I mention yhat this all worked for 12 years without a problem befor last year?
 
ELA

ELA

Senior Member
Occupation
Electrical Test Engineer
You mention it happens on turn off. Is it possible that there is a transient ( inductive?) generated when turned off and it causes an insulation breakdown to occur?
Possibly aggravated by moisture allowing for a lower breakdown voltage level.

You should be able to test for these transients fairly easily if occurring.
 
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dave h

Member
Location
Bergen, New York
This is the only explanation I can come up with, but how do I prove it, find it ? The fact that it only happens during the rain and while turning off makes my suspensions stronger with the transient explanation.
 
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Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Winging it here, but let me start the thinking in a direction and see if the experts here can help. First, what are all the potential things that can cause a loud bang in the locations you described and then are they feasible. I'll start

High amperage at the contact points. unlikely because fuses and CB's limit that and extensive testing has been done to try and discover

Wires banging against the wall of the conduit or boxes. I am thinking this would be from magnetic forces, and again requires high amperage see above.

high voltage at the contact points. The only thing I can come up with that can cause the bang. So now, what could cause that? And/or how to identify?


Any other ideas about what could cause the bang?
 
kwired

kwired

Electron manager
Location
NE Nebraska
Strathead said:
Winging it here, but let me start the thinking in a direction and see if the experts here can help. First, what are all the potential things that can cause a loud bang in the locations you described and then are they feasible. I'll start

High amperage at the contact points. unlikely because fuses and CB's limit that and extensive testing has been done to try and discover

Wires banging against the wall of the conduit or boxes. I am thinking this would be from magnetic forces, and again requires high amperage see above.

high voltage at the contact points. The only thing I can come up with that can cause the bang. So now, what could cause that? And/or how to identify?


Any other ideas about what could cause the bang?
Click to expand...

Inductive kickback? Don't know just a suggestion.
 
S

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
kwired said:
Inductive kickback? Don't know just a suggestion.
Click to expand...

Showing my ignorance, I didn't even know what indcutive kick back was. I tried looking it up on Google, and did see that lo and behold it increases the voltage when a switch is open indicating that I was at least thinking right. The quick look suggested diodes opposite the normal current direction, which confuses me. Isn't induction a property of an AC circuit? So isn't there no such thing as normal current direction?
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
since the flash was in the CB panel, I would be looking in there to see where the black marks are.

As a guess, I am thinking maybe on the neutral bar?

Maybe a loose neutral? maybe a loose neutral at the POCO xfmr?
 
T

T.M.Haja Sahib

Guest
Just a thought. There is somewhere fault in the wiring being aggravated by rain. May be revealed by meg with 500V rating. The breakers should be test tripped to check their functioning, because their breaking capacity seem to be exceeded during switching off causing extensive sparking and being dangerous to operate.
 
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