Strange Electrical Issue

[Rudy]

Half of my bay lights are on one 20 amp circuit, the other half on a separate 20 amp circuit. Since the panel is 3 phase, and the breakers are not next to each other (One intervening circuit breaker between the two)...I'd assume that they are on separate phases.

I have a situation where BOTH breakers intermittently trip AT THE SAME TIME.

While troubleshooting tonight I had a situation where, after resetting they Both popped again.

I reset one breaker and waited.

I reset the other.....and both popped.

This makes no sense to me. Any ideas?

By the way, I replaced both of them a month ago with new breakers.

 

[MEP001]

They're probably sharing a common wire for both circuits.

If you reset the "other" breaker" before you reset the first one, will it still trip?

 

[Rudy]

The condition is intermittent.....so I can't answer that question. It just so happened last night, that I was able to reset the first breaker....and then upon resetting the second one, that they both popped. I was thankful that I saw this, since it's a major clue to what's going on. Before this time....I'd go to the wash, and just see both breakers popped.

Would they possibly be wired with a shared common? Is this even allowed? It doesn't sound right.

If Leg A had 20 amps flowing, and Leg B had 20 amps flowing.....there'd be 40 amps flowing through a shared common...yes? Each leg would require it's own own common wire.

Another possible clue...

I read on a thread (that I googled) that some problems can be traced to issues with the feed which feeds the Main Panel.

I noticed that when one of my Cat 3535 pumps starts up, my Uninteruptable Power Supply which protects my computer "beeps" about twice. The UPS has an undervolt warning.....so I wonder if this is another possible piece of the puzzle???

 

[robert roman]

Effect must have cause.

Overload, short or ground fault causes breaker to trip.

Since you replaced breakers, that potential should be eliminated.

If you haven’t many any changes to load, wiring or other factors as in everything was working fine before hand, I would examine light fixtures (end use) for potential issues – leads, connections, receptacle, corrosion.

 

[Robert Bailey]

I noticed that when one of my Cat 3535 pumps starts up, my Uninteruptable Power Supply which protects my computer "beeps" about twice. The UPS has an undervolt warning.....so I wonder if this is another possible piece of the puzzle???

Motor could be going bad, or the load balance could be off. Just a pain in the rear to cal. the load and balance the panels.

always more to panel work than just putting in a breaker and connecting wires

 

[mac]

Please let us know what you find out about this. I hate it when I get called out to troubleshoot something like this, but love to watch it from the sidelines. There does have to be something in common for this to happen. You might start by pulling the cover off of the breaker panel and looking real close at the wiring associated with this. One thought would be if you have a lighting contactor that powers both circuits.

 

[2Biz]

Another possible clue...

I read on a thread (that I googled) that some problems can be traced to issues with the feed which feeds the Main Panel.

I noticed that when one of my Cat 3535 pumps starts up, my Uninteruptable Power Supply which protects my computer "beeps" about twice. The UPS has an undervolt warning.....so I wonder if this is another possible piece of the puzzle???

That should be easy to check. Check the voltage on each supply line coming into the panel while kicking on the cat pump. Do the same for the cat pump motor. It could be drawing too much current at startup thats dropping voltage or like you said, might be an incoming line issue to the main panel....

Regarding the "Shared Common Issue". Can't you tell if there is a common going to each circuit from the main panel? If both circuits use a different conduit attached to the main panel, this should tell you what you've got. Also, make sure all you're connections in the panel are tight. I've seen loose connections cause problems too...

 

[car washing systems inc]

The condition is intermittent.....so I can't answer that question. It just so happened last night, that I was able to reset the first breaker....and then upon resetting the second one, that they both popped. I was thankful that I saw this, since it's a major clue to what's going on. Before this time....I'd go to the wash, and just see both breakers popped.

Would they possibly be wired with a shared common? Is this even allowed? It doesn't sound right.

If Leg A had 20 amps flowing, and Leg B had 20 amps flowing.....there'd be 40 amps flowing through a shared common...yes? Each leg would require it's own own common wire.

Another possible clue...

I read on a thread (that I googled) that some problems can be traced to issues with the feed which feeds the Main Panel.

I noticed that when one of my Cat 3535 pumps starts up, my Uninteruptable Power Supply which protects my computer "beeps" about twice. The UPS has an undervolt warning.....so I wonder if this is another possible piece of the puzzle???

The common will only see the inbalance of the 2 if 1 leg is drawing 15a and the other leg is drawing 18a the common would see 3amps. If you think your trouble is the cat pump you should do an amp test on each leg and see if one is much higher than the others at start up and running.

 

[Rudy]

I did indeed today find a single common for the two lighting legs. You explanation now makes sense since the two legs would be operating at different phase angles.

I tightened every connection in the main panel....especially the commons where they attach to the bus bar. I don't like the way that the common goes to the first fixture, connects with wire nuts, and then leap frogs to the next fixture....on and on. It seems that if the first connection in the chain becomes iffy.....everything downstream becomes faulty. I tightened all the wire nuts....so maybe this was my issue.

In fact, with a single common wire....a faulty connection would indeed cause BOTH legs to heat up and trip the breaker....yes?

BTW.....thanks for the myriad of replies. You guys are the best.

 

[MEP001]

I've had the same problem for years where two or three lighting breakers would trip when the lights come on. I've suspected the entire time that it was to do with the shared common between those three circuits - since I switched to an astronomic timer and have the rear bay lights come on a half-hour later than the rest, the problem hasn't happened again.

The electricians who did the wiring said it's to code, and I'm sure it would have failed the thorough inspection if it wasn't. The problem was much worse at first - the electrician's attempt at a solution was to break up the lights to more breakers, which helped but didn't completely solve it. Their claim was that the metal halide lights have a high inrush when they first come on - I've since tested it, and they don't. They come on at around 2A for the circuit and build to 12A as they get to full brightness.

 

[Rudy]

Ugh. After tightening every connection in the panel yesterday, the lights came on normally last night. Before closing up the panel today, I decided to turm them on to check. Bam. Both breakers popped. Today it's a rain day so it's quiet here. When the breakers popped, I could hear the UPS give the undervoltage "beeps" I referred to in an earlier post....hence another clue. Something causes the voltage to drop (intermittently) when the lighting contactor closes.

A clamp on Ammeter shows about 9.4 amps one one leg, and 4.8 on the other. When I "clamp" the single common, the reading is about 7 amps. (The leg with 9.4 amps has an additional 400W halide on it).

Does this sound consistent with an issue with the single common? Would a bad connection (or faulty wire etc.) be a cause for an undervolt situation for a very brief moment.

Lastly, my problems didn't crop up until I replaced several fixtures (both legs) with CFL bulbs. In each fixture, I swapped out the old 175 Metal Halides for (4) 23W CFL bulbs. I've read that the "inrush" with CFL's can create problems. Again, the inrush is for milliseconds, and I don't think that would be enough to heat up, and trip a circuit breaker......would it?

 

[2Biz]

Would it be worth putting in a time delay breaker to see if it fixes the problem?

 

[MEP001]

How hard would it be to run a separate common to each circuit?

Will your clamp-on meter read peaks? I'd be interested to see what the amperage is getting up to when the breaker trips. Vacs typically run over 60A when they first come on and don't trip a 20A breaker.

 

[wash4me]

The shared neutral won't cause problems if it's done correctly. It will actually only carry less power because it's only the difference in the load on the 2 phases. Even if it's wrong and it's loaded to double it doesn't trip breakers because the neutral isn't run through the breakers. One method is to install small fuses at each fixture and see which one blows.

 

[mjwalsh]

The shared neutral won't cause problems if it's done correctly. It will actually only carry less power because it's only the difference in the load on the 2 phases. Even if it's wrong and it's loaded to double it doesn't trip breakers because the neutral isn't run through the breakers. One method is to install small fuses at each fixture and see which one blows.

From my limited experience ... Just a heads up & something to consider... depending on the specifics ... a shared neutral can potentially cause an electrical shock hazard & also an intermittent exasperating "ground loop".

http://en.wikipedia.org/wiki/Ground_loop_(electricity)

The shock hazard comes into play when a maintenance person assumes the shared neutral is dead ... but it turns out not ... because all breakers are not off! If I remember right ... it seems like I read somewhere that shocks from neutral wires can be even more dangerous than from hot wires.

mike

 

[slamdvw]

high leg?

Just for the sake of argument, measure from phase to ground (or neutral ) on the breakers that keep tripping.

A 120 v ballast may or may not survive very long being fed 208v, but it's worth a shot.

The individual 'test' fuses is also a good idea.

 

[Rudy]

After literally pulling my hair out....I THINK I found the problem.

I've spent hours reading about shared neutrals, CFL inrush issues etc.

As a first step, I decided to start pulling a dedicated neutral to each leg of lighting (and avoid the shared neutral as an issue). At the first fixture, as I was struggling to pull the first neutral, there it was. Burned wires, right where they depart the fixture and enter the conduit. The neutrals were OK, but the two hot legs (which feed my 2 lighting legs) were both burned. Each wire (a black and a red) were both intact by only a few strands of copper each. This fixture had been converted to CFL, but the original fixture was a 175 W metal halide. Apparently, a ballast had overheated sometime, failed, and damaged the wires.

Rather than pull all new wires back to the panel, I cut the damage out....installed a plastic junction box....and spliced new wires to the fixture. All has been well for several nights....so we'll see.

Your advice on this forum was very helpful.......

 

[Kevin Reilly]

Rudy, I just replaced a 400W MH with a 105 CFL and it was a great satisfaction to rip out all the crap that was in that fixture. I cut the power leads and when I hooked up the CFL with a wire-nut the power wire cover was brittle and fell (broke off in pieces.) I cut it back to where it wasn't brittle and made the connection!

 

[Jeff_L]

Rudy - sorry I didn't reply earlier as I've been out of town for awhile and haven't kept up on the forum until yesterday and today. I've ran into this issue a couple of times where the wires in the wall pack were laying on the metal shield of the fixture and over the years the heat had slowly melted through the insulation creating a short. I have this problem right now as one circuit continues to trip. The problem is going through each wall pack looking for the short. Uggh...

 

[MEP001]

I haven't had wiring melt yet, but so far four transformers have burned up and shorted out. Sometimes it smokes the inside of the lens to make it easy to spot which one on the circuit went out, but when it doesn't I have to open them up one at a time and unhook the wires to find it.