Breaker tripped and I don't know why.

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JES2727

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Hello,
I was called to an office building today that had lost all their parking lot lights. I quickly discovered that the breaker had tripped. The lights are 480 volt, so I didn't want to be too hasty to reset the breaker. I disconnected the feeds from the contactor and used my Fluke to check for a short or a ground fault. I found none, though I did measure some ohms between phases, as I expected. I reconnected the feeds, reset the breaker, turned on the switch at the time clock and the lights came on. They burned for about an hour until I turned them off and left the site. Any ideas as to why a breaker trips for no apparent reason? I suspect a bad ballast, but only because I can't think of any thing else. Is there a better troubleshooting method to follow? Thanks for any help.

P.S. : I know someone will ask : No, I wasn't wearing any PPE when I reset the breaker and turned on the lights.
 
A. Breakers DO NOT TRIP FOR NO REASON.
B. What size CB?
C. Use a megger..........


Proper tool for the job, if you do not have a megger contact a firm that does.
 
It's a 30 amp breaker. Each wire was pulling about 9 amps while the lights were on, except for during start-up. The ambiant temp in the area around the panel is over 90 degrees F.
If the problem persists I will use my megger. I presume I would have to open all splices and meg each wire in every direction, correct?
 
JES2727 said:
If the problem persists I will use my megger. I presume I would have to open all splices and meg each wire in every direction, correct?
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Maybe it will come to that, but you can start with phase to ground, and see how that hashes out.
 
Did you check the current draw of the circuit with an Amp meter? At this time of year it colder and the breakers with take longer to trip if they are drawing just a little over the current rating. Did you check the termination in the panel for loose connection ( if this is an exterior house panel there could be a bad connection, corosion).

Edit: a day late and a dollar short here.
 
JES2727 said:
It's a 30 amp breaker. Each wire was pulling about 9 amps while the lights were on, except for during start-up. The ambiant temp in the area around the panel is over 90 degrees F.
Click to expand...

9 Amps doesn't power very many pole lights. Were all the lights back on when you reset the circuit?
 
growler said:
9 Amps doesn't power very many pole lights. Were all the lights back on when you reset the circuit?
Click to expand...
Hey, that's using the old noodle. I know that a ballast can fail in such a way that it will trip the breaker. Reset the breaker, and the fixture is now dead and has declared itself. If it's an installation you're not famaliar with, however, it is always up in the air as to what fixtures might have been failed or had bad lamps for some time, and which may have failed concurrently with the breaker tripping.
 
Sounds like an intermittent short. The only way to trace this down is to 'divide and conquer'. Remove a portion of the circuit and see if the problem is solved or persists.

What happens is there is a bare hot wire near a ground. When the wires are not used, there is no short. But turn them on, and heat starts to build up, and things start moving. After a while, Boom!

Case in point from the last time I experienced this:

DSC05328a.jpg


DSC05329a.jpg


School had an exterior lighting circuit with this same problem. I kept disconnecting parts of the circuit until I found it... an intermittent short in an in-ground HID for the flag out front. Sometimes it would trip in a couple minutes, sometimes after several hours.
 
growler said:
Did you check the current draw of the circuit with an Amp meter?
Click to expand...
Yes. 9 amps per leg.
growler said:
9 Amps doesn't power very many pole lights. Were all the lights back on when you reset the circuit?
Click to expand...

This particular circuit feeds 8 pole lights. Last time I visited the site, 7 poles were lit. I don't have a bucket truck so I didn't make the repair, and neither did anyone else. Today, 6 poles were lit.
mdshunk said:
I know that a ballast can fail in such a way that it will trip the breaker. Reset the breaker, and the fixture is now dead and has declared itself.
Click to expand...
That's what I'm thinking....
 
If the breaker is off when I get there or I can turn off the power the megger is in use. while there are cases, especially with pole lights with PVC, where a meggger might miss a fault, in my expierence, if there is an intermittent short in PVC due to moisture, carbon ect the megger will be a vast improvement over other test methods.
 
i meg my wires, but haven't megged anything with devices attached - never knew if I would damage anything. You meg with the fixtures and all attached ?
 
It's kinda hard to fix when it aint broke huh?

I have seen a ballast that would not trip till it was on for quite a while.

I've also seen faulty undergound wiring in PVC that would take a while to trip.

I usually take the "wait and see" approach.
 
JES2727 said:
This particular circuit feeds 8 pole lights. Last time I visited the site, 7 poles were lit. I don't have a bucket truck so I didn't make the repair, and neither did anyone else. Today, 6 poles were lit.
Click to expand...


Jes2727, I don't have a bucket truck either ( don't really want one ) but I have the next best thing. I have used a company for years that does nothing other than outdoor ( mostly parking lot ) lighting. They have plenty of trucks that are stocked with all the right parts and techs. with the right experience to repair any parking lot lighting. I just give the customer their card. This company doesn't do anything other than lighting so if they run into a problem that requires any inside wiring then they throw that my way. We all get to do the work that we are best trained for and everyone stays happy.

Send these suckers an invoice and recommend a lighting contractor, find a good lighting contractor. Doctors charge to send you to a specialist all the time.
 
I once had a problem like this. Would get a call every few days that the sign wasn't working and I would check it and reset the breaker and sit there for a half hour or so and all would be fine. One night I happened to be there a little longer when it finally tripped. Turns out that someone had added some exterior lights to the same circuit, but on a different timer and when they would come on it would be just enough to trip the circuit. No real problem other than to many amps.
 
JES2727 said:
Hello,
I was called to an office building today that had lost all their parking lot lights. I quickly discovered that the breaker had tripped. The lights are 480 volt, so I didn't want to be too hasty to reset the breaker. I disconnected the feeds from the contactor and used my Fluke to check for a short or a ground fault. I found none, though I did measure some ohms between phases, as I expected. I reconnected the feeds, reset the breaker, turned on the switch at the time clock and the lights came on. They burned for about an hour until I turned them off and left the site. Any ideas as to why a breaker trips for no apparent reason? I suspect a bad ballast, but only because I can't think of any thing else. Is there a better troubleshooting method to follow? Thanks for any help.

P.S. : I know someone will ask : No, I wasn't wearing any PPE when I reset the breaker and turned on the lights.
Click to expand...


megohmmeter, put a meger on the circuit. There are various ways to do it but this tool will find everything from bad insulation on the feeder wires, bad insulation in the ballast to a wire nut setting in a box full of water.
 
hardworkingstiff said:
Have you ever heard the conductors slapping against the pole when the wind was blowing?

Maybe a wire with a nic?
Click to expand...

I've seen make-ups in the poles with split-bolts because they're wired with #6s or larger, and the original installer skimped on the tape wrapping them up. After a few years, the bouncing around wore through the tape and would short out to the inside of the poles.

This is an easy fix, but time-comsuming. Just buy a log of quality tape and open every hand-hole....
 
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