Why do they both trip???

[K8MHZ]

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)?

They look like they are in the on position to me.

 

[steve66]

My guess is that you need to turn the magnetic settings up on all 3 breakers. A coordination study would tell you how much.

Is there also a transformer on the 70 amp feeder?

Maybe when they test the generator, and when the transfer happens, if the timing is just right there is enough inrush on both feeders to cause both breakers to trip, and one also has enough to trip the main.

Kudos to you for not turning everything to "max" as soon as one breaker tripped. I think that's the normal troubleshooting method.

 

[iwire]

What is the 30-45kva estimated transformer exactly feeding?

A 208Y/120 panel for required emerngency circuits only.

Both the 70 and the 100amp conductors are separate or do they share conduit/raceways at any point?

Other than the panel separate,

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.

See my response to George.

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)

This is not what I am asking about.

I understand why breakers in series with each other can both trip it is actually pretty common.

 

[mbrooke]

They look like they are in the on position to me.

:slaphead: Just looked at the pics again. They are. :ashamed1: My eyes latched onto number 22 and 34 :lol:

 

[gadfly56]

I took a quick look at the bulletin for these breakers and it look like you may want to move the adjustment off of "min" for the 200 and the 70 for the transformer feed per their suggestion. That doesn't explain the 100 amp going, however.

 

[mbrooke]

A 208Y/120 panel for required emerngency circuits only.

Just lighting or any motor/inrush loads on it as well? Typical Delta wye transformer, right?

 

[kwired]

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.

Which is why I mentioned I don't know where they should be set, but as is they possibly are at a lower magnetic trip setting then all the breakers that don't have an adjustable magnetic trip, which is very well why those three are the only ones that are tripping.

 

[iwire]

My guess is that you need to turn the magnetic settings up on all 3 breakers. A coordination study would tell you how much.

Respectfully I see no connection between the mag settings and two breakers protecting different circuits tripping at the same time.

If there is a fault on the 100 amp breaker how is that tripping the 70 amp breaker located across from it?

Is there also a transformer on the 70 amp feeder?

Yes.

Maybe when they test the generator, and when the transfer happens, if the timing is just right there is enough inrush on both feeders to cause both breakers to trip, and one also has enough to trip the main.

Hmm, hmy: this exact issue has happened in the past and I was able to fix it by programing in a transition delay into the transfer switch.

Instead of transferring directly back to utility from the live generator it paused for a time in between. It seemed to have worked for me twice in the past.

Sitting here at my desk I doubt they run the genset in the middle of the night for testing but I really do not know. I will tell you this I am going to check on the exerciser schedule and if they exercise with load. I am going back tonight to assist the testing company.

Kudos to you for not turning everything to "max" as soon as one breaker tripped. I think that's the normal troubleshooting method.

It is just not a decision I make and it comes up pretty often.

 

[mbrooke]

Which is why I mentioned I don't know where they should be set, but as is they possibly are at a lower magnetic trip setting then all the breakers that don't have an adjustable magnetic trip, which is very well why those three are the only ones that are tripping.

I understand and I fully agree.

 

[iwire]

I took a quick look at the bulletin for these breakers and it look like you may want to move the adjustment off of "min" for the 200 and the 70 for the transformer feed per their suggestion. That doesn't explain the 100 amp going, however.

Hey thanks.

 

[ron]

I may have missed it, but how often does this happen?

Is it possible that it is associated with a lightning strike in the area?

 

[mbrooke]

Respectfully I see no connection between the mag settings and two breakers protecting different circuits tripping at the same time.

If there is a fault on the 100 amp breaker how is that tripping the 70 amp breaker located across from it?

Taking a shot as answer Steve :thumbsup:


Its possible that when the 100amp feeder faults the voltage drop causes motors on the 208 volt side to stall, pulling excess current and taking out the 70amp breaker in the process.

Another possibility is that nothing has faulted- rather the ATS switching from utility to gen and gen to utility is causing inrush that just happens to be over the mag trip of each (70 and 100amp branch) and the total of each branch being over the 200amp main.

I know it sounds like a stretch, but its not impossible.

 

[iwire]

Just lighting or any motor/inrush loads on it as well? Typical Delta wye transformer, right?

Maybe inrush loads doubt it but can't say, yes Delta/wye.

Keep in mind, in qualified in house engineering here without fear of spending some money. The total load on that 200 amp panel is likely less then 40-50 amps with the branch circuits and feeders combined.

If the breakers are sufficient not trip to from inrush when I energize the transformers I am having a hard time seeing an inrush on the secondary side tripling these primary side breakers.

 

[Jraef]

The reason why it's not that uncommon for two largish frame breakers to trip during the same event, especially in an uncoordinated system, is explained by the difference in the sensing of a fault and the actual interruption of it. Sensing, especially with electronic trips such as these, is fairly consistent. But interruption involves unlatch time, contact separation time and arc extinguishing time. Those time frames are almost never the same, and the larger the frame size, the longer it takes. So the same even is sensed simultaneously and initiates the trip in both of them, but although the smaller breaker opens first, the process had already started on the larger one and is irreversible once the unlatch has taken place, even though the fault may have already been cleared by the smaller breaker down stream. This is one of the main reasons why you do a coordination study. It looks at not only the trip settings, but st the total fault clearing times in order to know where the trip settings should be.

Now how you had two down stream breakers trip with the main is a different story. I like the cross connection theory on that one.

 

[mbrooke]

Maybe inrush loads doubt it but can't say, yes Delta/wye.

Keep in mind, in qualified in house engineering here without fear of spending some money. The total load on that 200 amp panel is likely less then 40-50 amps with the branch circuits and feeders combined.

If the breakers are sufficient not trip to from inrush when I energize the transformers I am having a hard time seeing an inrush on the secondary side tripling these primary side breakers.

I would be too, however there are some loads, or combination of loads which can dwarf the inrush of its transformer.

 

[iwire]

Its possible that when the 100amp feeder faults the voltage drop causes motors on the 208 volt side to stall, pulling excess current and taking out the 70amp breaker in the process.

I am going to consider that next to impossible even if I believed there were motor loads involved.

So is this stalled 208 motor tripping the primary 70 amp breaker and 200 amp main breaker in the instantaneous range or the overload range?

Another possibility is that nothing has faulted- rather the ATS switching from utility to gen and gen to utility is causing inrush that just happens to be over the mag trip of each branch and the total of each branch being over the 200amp main.

I know it sounds like a stretch, but its not impossible.

That one I am going to look into. I have seen that at least twice.

 

[kwired]

Respectfully I see no connection between the mag settings and two breakers protecting different circuits tripping at the same time.

If there is a fault on the 100 amp breaker how is that tripping the 70 amp breaker located across from it?

May not be any fault, just a transient condition that you have not discovered. Such condition coming from the supply is definitely passing through the main, depending on types of loads supplied you may have transient current on several breakers from that panel, but those three breakers are the only ones with magnetic trip setting low enough that they are impacted.

Not saying that is your problem, but should be taken into consideration.

 

[mbrooke]

I am going to consider that next to impossible even if I believed there were motor loads involved.

So is this stalled 208 motor tripping the primary 70 amp breaker and 200 amp main breaker in the instantaneous range or the overload range?



That one I am going to look into. I have seen that at least twice.

But let me ask you this... why would the sudden voltage disturbance from an ATS cause tripping and not the voltage disturbance from a fault on the out building feeder?

 

[iwire]

May not be any fault, just a transient condition that you have not discovered.

Fair enough and it is reasons like that we have had a power recording meter on it for some time in the past. Never tripped while it was in place.

Tonight they will be testing the underground run with better methods than we have. It should be interesting.

In most cases we would have simply replaced the conductors at this point but its about 2,000' of I think 500 kcmil, copper for sure and to top it off the a floor standing ATS has to be moved out of the way to do the pull.

We would have a window from 11PM to 6AM to make it happen if that is what need to get done.

 

[iwire]

But let me ask you this... why would the sudden voltage disturbance from an ATS cause tripping and not the voltage disturbance from a fault on the out building feeder?

Simple

One if literally a zero voltage event, when the ATS transfers it open the circuit entirely for a time.

On the other hand a short in feeder 1 is only going to drop the voltage in feeder 2 a small amount.

Again a very stout supply here, this customer wont even use a POCO trans, they take the service at 13.8 and use an NEC sized privately owned unit.

This ATS and panelboard is likely not more than 150' of conductor away from that transformer.