Street lights circuit breaker intermittent tripping issue

[sw_ross]

Different situation than other thread on parking lot lighting.

From the control box there are 2 circuits, 1 heads east, the other heads west. There are maybe 22-28 street lights on each circuit (just estimating).
Each one is on a 2-pole 50-amp breaker. The panel is single phase 120/240. The lights are daisy chained with direct burial wire, not in conduit.
The 2 circuits are controlled by a photo-cell through a contactor.

The lighting circuit has worked fine for many years.
The lights are HPS, not sure of the wattage. It appears that on each circuit the lights are set up for alternating phases (L1, L2, L1, L2.... ) sharing the neutral.

One circuit (heading east) periodically trips the breaker. It probably happens about every 2 week, so not consistent.

Nothing related to the actual lights has changed other than general maintenance by the city maintenance guy.
I checked everything in the control box and everything seems ok. Voltage is fine, photo-cell is working fine, contactor is pulling in and releasing fine.
Current draw on each leg is around 12 - 19 amps. Also checked current draw on neutral, it was around 11 amps.

Without it being a consistent issue it's hard to troubleshoot. If it was consistent I would play around with splitting the circuit up (L1, L2) and try to narrow down the issue that way. The lighting circuit has work without issue for years until this started happening (within the last couple of months).

One theory that the city maintenance guy has is the the POCO bored in the vicinity about a year ago and maybe they nicked a line.,
I'm not sure what troubleshooting steps to take until it becomes a more consistent problem.

 

[480sparky]

So many different possibilities. I've seen splices in the handholes that have been worn down enough over the years to expose bare copper so when the wind blows, they swing against the inside of the pole and pop the breaker. Direct burial cable can take years to manifest a nick to where it will trip when there's sufficient moisture in the ground. At the top of the poles, where the conductors transition from the pole itself to the arm, there may be a worn spot in the insulation. It may be a failing component in one of the lights themselves... or a bared hot wire that gets moved by the wind.

My first step would be to take all the pole wiring off the circuit and megger the underground line. If it fails, then it's just a matter of using a fault locator.

 

[sw_ross]

So many different possibilities.
My first step would be to take all the pole wiring off the circuit and megger the underground line. If it fails, then it's just a matter of using a fault locator.

I figured someone would mention megger....

My problem is I don't own one, and if I did,I've never been taught how to use one.
Im not opposed to buying one, I know to be a good service electrician you should have one, and this situation would probably be a good justification to buy one.

I have watched lots of youtube videos about using them. I just want to have confidence that if I show up with one that I know how to use it. And that I don't go and damage customer owned equipment because I didn't know what I was doing!

 

[ptonsparky]

I figured someone would mention megger....

My problem is I don't own one, and if I did,I've never been taught how to use one.
Im not opposed to buying one, I know to be a good service electrician you should have one, and this situation would probably be a good justification to buy one.

I have watched lots of youtube videos about using them. I just want to have confidence that if I show up with one that I know how to use it. And that I don't go and damage customer owned equipment because I didn't know what I was doing!

Now that you brought it up, go buy one. Underground testing is easy. Isolate both ends of the conductor and test.
RTFM. Doing nothing, gets nothing done.

 

[sw_ross]

Recommendations?
Fluke 1587?
What features should I look for...

 

[petersonra]

I concur with the megger idea. They are easy to use. just isolate the conductors from any equipment and light the conductors up. They are not perfect and don't find every insulation problem every time but they are pretty good at it. Lots of videos from manufacturers that tell you how to use them if written instructions are not enough.For what you are doing just about any lower cost megger will work, even the $20 ones sold on eBay.

I would also be inclined to check the terminations for whiskers. A magnifying glass and dental mirror can be quite helpful.You might also want to take a very close look at the contactor. Look for black streaks or other discoloration or anything else unusual.

 

[Sierrasparky]

Direct burial to me is the give away.
Megger the wires , or separate and check.
Otherwise it could be a ballast ?????

 

[synchro]

While less likely, it's also possible the breaker is no longer working properly. Are they "high magnetic" or a silmilar type to handle the ballast inrush current?

 

[sw_ross]

While less likely, it's also possible the breaker is no longer working properly. Are they "high magnetic" or a silmilar type to handle the ballast inrush current?

The breaker is a Siemens QP plug-on.

At this time, given the options of getting into each light pole on the circuit, the maintenance guy wants to just keep resetting the breaker until it becomes a more constant issue and he’s forced to deal with it.
Typical maintenance guy...

We talked about the breaker. He said he might change it out himself just to see.

I don’t think that’s the issue since it’s worked fine for at least 7 years that he’s been there, but what do I know.

Like everyone has said it could be a number of issues from the direct burial line to an issue within one of the light poles.

We do get some pretty strong winds at times, and it blew pretty hard over the weekend last. That’s a variable that I’m going to keep an eye on for sure.

 

[oldsparky52]

We do get some pretty strong winds at times, and it blew pretty hard over the weekend last. That’s a variable that I’m going to keep an eye on for sure.

I'd also keep track of rain events to see if that has any correlation to the breaker tripping.

 

[ptonsparky]

We use Fluke 1507s but IDK if that is a current model or not. They have a good low ohms scale as well.

 

[LarryFine]

You mentioned two MWBCs, suggesting 2p breakers. Temporarily install 1p breakers to isolate which of the four circuits is the culprit.

 

[sw_ross]

You mentioned two MWBCs, suggesting 2p breakers. Temporarily install 1p breakers to isolate which of the four circuits is the culprit.

Thanks! That’s a good idea

 

[LarryFine]

Thanks! That’s a good idea

I do that once in a while.

 

[Cow]

I'm with the rest, I'd megger it. And then bring in the fault locator if the problem is between splice points. I also use a Fluke 1507. Worth every penny of what I bought it for on Ebay 10+ years ago!!

Standard procedure to get a feel for what kind of shape it's in, meg it hot-gr and see what you get. 500v test voltage. Usually db wire gives VERY low readings, especially when it's a long run.

After you test, then it's just divide and conquer. Break the circuit in half, again and again until you get it narrowed down. Inline fuseholders in the poles would make future troubleshooting easier, because if it's a pole/fixture problem the fuse blows and keeps the rest of the circuit online.

Something else to keep in mind, you may locate and fix the problem but meggering when you finish is a good idea. I can't count how many times I've found the main problem, but then have found smaller issues that haven't quite made it to into a major problem yet. It's nice to catch those and repair them before they start tripping the breaker or causing other issues while you're already there.

 

[480sparky]

If you have an ammeter that can record maximum current, you might be able to narrow it down to whether it's a short or an overload.

 

[ptonsparky]

In line with Cows comments. We, test, locate fault, cut open bad spot and repeat before making repairs. We had some underground to a pivot this late summer that had only one ‘open’ but so many other faults it wasn’t worth the repair.

 

[hillbilly1]

You can also rent meggers, if you don’t have enough use to justify buying one. Another test that usually works well, but better at 480 volts, is to use your amp clamp to enclose all of the circuit conductors (both hots and neutral, if line to neutral loads are used), you should get zero amps if there is no fault to ground present. If you do get an amp reading, use the divide and conquer method as others have said to narrow it down.