Why do they both trip???

[iwire]

Here is the deal, for long time we have had a customer that has some breakers that have been tripping.

Here is the panel I am dealing with, it has a 200 amp main breaker at the top and down at the bottom you can see two - 3 pole breakers, a 70 and a 100.

The other night I went there and the 200 amp main, 100 amp feeder and 70 amp feeder were all in the tripped position.

Below is the main breaker.

Here are the two 3-pole breakers

The 200 amp breaker supplies the panel from an ATS right beside it. In turn the ATS is supplied from switch-gear very close by. I would say the supply is very stiff, over done in house engineering. (Not a complaint, just saying they use a lot more copper than is likely required)

The 100 amp breaker supplies a panel 400'-500' away in a separate structure. This is an underground run, around 500 Kcmil copper in PVC. The load in less than 20 amps on all three legs. The panel supplies LED egress and exit lighting, a fire alarm booster panel and other small loads.

The 70 amp breaker is the primary supplying a transformer directly above the panel, lets say 15' to 20' of conductor from breaker to transformer. I did not check but suspect the transformer is a 30-45 kVA unit. 480-208Y/120.


We all suspect the underground run is failing, each time there has been a trip over the course of maybe two years and five or six trips the ground has been wet or moist.

I did use a basic mega meter on it and it went to the end of the meters scale.

Monday night I am meeting a testing company on site to do some type of advanced testing on the conductors.

Now here is the real question I have.

Regardless of the fault being on the 100 amp breaker or the 70 amp breaker why are they both tripping?

I understand the main and one feeder going to the tripped position at the same time but why are two unrelated feeder breakers tripping at the same time?

This has happened each time, always both breakers tripped.

Grasping at straws while there the other night I decided to move one breaker away from the other on the thought one was somehow tripping the other?? Magnetic field?? Just the sharp rap of one breaker tripping causing the other to go??? I have no clue but I did move the breaker.

Anyone have some insight? A technical reason for this? Poltergeists?

 

[Dennis Alwon]

My first thought was you need a coordinated study and an adjustment needs to be made on the main. It seems that there can be a large load on the same area so that the breakers are heating up. My other guess is possible poltergist

 

[iwire]

My first thought was you need a coordinated study and an adjustment needs to be made on the main. It seems that there can be a large load on the same area so that the breakers are heating up.

All three breakers have negligible loads on them. They supply only required emergency circuits. You can run a lot of LED fixtures exit signs at 277 volts without seeing much draw.

My other guess is possible poltergist

:thumbsup:

Its as good as anything I can come up with. I am really at a loss to explain why both breakers trip.

 

[Dennis Alwon]

If the 3p breaker on the bottom controls lighting then I am guessing that a ballast is heating up and somehow shorting to ground. The main can trip if it is weak or it is not set correctly. Isn't that an adjustment I see or does that changes the actual amperage of the breaker.

 

[iwire]

If the 3p breaker on the bottom controls lighting then I am guessing that a ballast is heating up and somehow shorting to ground. The main can trip if it is weak or it is not set correctly. Isn't that an adjustment I see or does that changes the actual amperage of the breaker.

The issue I am having is why do both the 100 and 70 amp feeder breakers always trip at the same time*. They supply separate loads.

It is as odd as having two branch circuits trip at the same time repeatedly and only one of the circuits seems to have an intermittent fault.:huh:


(* To be clear, all I know for sure is both breakers are tripped when we arrive which is 30-120 minutes after the call came into us.)

 

[George Stolz]

Grasping at straws, but I would check to see that the 70A and the 100A are entirely electrically isolated on their load side. If they are not, a short circuit or ground fault on either would trip the other. The 200A being dialed to minimum would indicate that the 200A and the others would tend to be pretty close in a short circuit or ground fault horse race. I would google the scale for the 200A min/max settings and see what the dial does for certain, and turn it up an informed amount to get it to slow down a bit for the supplied breakers to finish sooner.

Edit: it could very well be that for a 200A trip plug, the max setting on that breaker is required for an actual 200A - I'd have to google the breaker spec sheets to know what it's controlling for sure.

 

[ptonsparky]

Grasping at straws, but I would check to see that the 70A and the 100A are entirely electrically isolated on their load side. If they are not, a short circuit or ground fault on either would trip the other. The 200A being dialed to minimum would indicate that the 200A and the others would tend to be pretty close in a short circuit or ground fault horse race. I would google the scale for the 200A min/max settings and see what the dial does for certain, and turn it up an informed amount to get it to slow down a bit for the supplied breakers to finish sooner.

Edit: it could very well be that for a 200A trip plug, the max setting on that breaker is required for an actual 200A - I'd have to google the breaker spec sheets to know what it's controlling for sure.

I wondered if they could have phases crossed to the wrong breakers but the wires appear to be different sizes. That and Iwire moved the breakers around so that theory was thrown out the window.

 

[George Stolz]

Not necessarily; two 12 AWG browns down the way from two different panels could be tied together by accident. I realize that one serves a transformer, so this shouldn't be the case, but I would want to hear "I have done a continuity check on the load side of both breakers on all phases and there is none" before I would discount it. Weird stuff happens.

 

[ptonsparky]

Didn't we have a poltergeist theory going in a thread not to long ago?

Time for a camera setup again?

 

[iwire]

Grasping at straws, but I would check to see that the 70A and the 100A are entirely electrically isolated on their load side.

For sure it could happen seen it a couple times with branch circuits.

In this case I can see the entire run from the 70 up the side of the panel and into a conduit up to the transformer.

OTH, The 100 amp feeder is a bit funky, the conduit to the other structure comes up under the floor mounted ATS that was a mistake so they ran a conduit out the top of the panel, over and down into the ATS using the bottom of the ATS to splice the say 1 AWGs on the breaker to the larger conductors running to the other structure.

 

[iwire]

I have done a continuity check on the load side of both breakers on all phases and there is none"

I can't say that but I can say I can see the 480 feeder to the trans.

It would be very very difficult for branch circuits to be mixed here. Buildings are separated by a 100'+ gap but there are bridge walkways with lighting so ...

Weird stuff happens.

You are right I cannot rule it out.

Testing for it with transformers involved is going to be more than a basic continuity test at these breakers.

 

[peter d]

Did you wear your PPE when you moved that breaker to the different position? :happyno::happyno:

 

[iwire]

Did you wear your PPE when you moved that breaker to the different position? :happyno::happyno:

:lol:

You think I moved those breakers hot?

The panel was dead.

Did I wear PPE to verify it was dead? Nope.

 

[augie47]

"Sympathy tripping"...
The 70 amp felt the 100 trip and joined in.

 

[mbrooke]

What is the 30-45kva estimated transformer exactly feeding? Both the 70 and the 100amp conductors are separate or do they share conduit/raceways at any point?


I am with George on this. Its possible the 70 amp and 100amp are crossed somewhere which is enough to show up on a ground fault.


As for the 200 and 100amp tripping (as already mentioned) uncoordinated breakers will fight each other when the fault current exceeds the instantaneous trip rating. This is especially true if the source impedance is low (ie plenty of available short circuit current as is common with high amp 480 volt services)

 

[kwired]

Looks like magnetic trip adjustment is set to minimum setting on all three in question.

Can't tell you where you should set them, but is possible you need to adjust them.

Transient occasionally comes from supply and trips them at these low settings?

 

[charlie b]

Time for a camera setup again?

That was my thought as well. One viable explanation is malicious mischief. But a camera pointed at the breakers could tell you something else: Do the two breakers actually trip at the same moment, or is there a delay between the trips?

Another possibility is that the vibration imposed upon the panel when the first breaker trips is enough to cause the second breaker to trip. Moving the one breaker might cure this problem. Another troubleshooting technique would be to put the breaker back into its original location, but move the circuit conductors to another breaker. If the two breakers once again trip together, with the one being closed but having no wires attached, it would indicate that the breaker is showing its age, and needs to be replaced.

 

[mbrooke]

Looks like magnetic trip adjustment is set to minimum setting on all three in question.

Can't tell you where you should set them, but is possible you need to adjust them.

Transient occasionally comes from supply and trips them at these low settings?

Believe it or not breakers are rarely (if ever) adjusted past the factory settings in most installations when installed.

However I agree those need to be raised, but not to knock on anyone its best left up to an engineer experienced in short circuit studies and selective coordination.

 

[mbrooke]

That was my thought as well. One viable explanation is malicious mischief. But a camera pointed at the breakers could tell you something else: Do the two breakers actually trip at the same moment, or is there a delay between the trips?

Another possibility is that the vibration imposed upon the panel when the first breaker trips is enough to cause the second breaker to trip. Moving the one breaker might cure this problem. Another troubleshooting technique would be to put the breaker back into its original location, but move the circuit conductors to another breaker. If the two breakers once again trip together, with the one being closed but having no wires attached, it would indicate that the breaker is showing its age, and needs to be replaced.

Ok, here is where my limited knowledge will shine, but I can't help but notice something in the pics. The 277 volt GE breakers I am familiar with all trip to the center, but in this pic they (the handles) appear to be in the off position. My question is did someone move them after to the "off" position or do these trip to the off position when called to operate automatically (short circuit)?

 

[iwire]

That was my thought as well. One viable explanation is malicious mischief.

Very limited access area, it would be lower management level mischief. Not out of the question but seems unlikely.

But a camera pointed at the breakers could tell you something else: Do the two breakers actually trip at the same moment, or is there a delay between the trips?

Very true.