Why do they both trip???

[kwired]

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.

You would replace all that copper without first checking where those magnetic trip settings should be set to?

If megging those conductors don't indicate a fault, I am not going to jump on the bandwagon of replacing them so quickly. You lose some credibility when you spend that kind of money and yet don't fix anything.

 

[iwire]

You would replace all that copper without first checking where those magnetic trip settings should be set to?

Where in the world did I even hint at that?

The entire point of the post you quoted was that this is too much money in copper and labor to just guess at things.

That is why a testing company is coming out tonight.

If megging those conductors don't indicate a fault, I am not going to jump on the bandwagon of replacing them so quickly.

I am mystified why you would think we would hire a testing company and then ignore what they find. :huh:

If the testing company says they are confident the conductors are good the conductors will not be replaced.

If the testing company says they are confident the conductors are bad the conductors will be replaced.

If the testing company says they can't say I am not sure what direction will be taken.

 

[mbrooke]

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.

What would you define as a small amount though? Even with a well lavished fault current supply, 500 conductors in themselves can pull some very generous fault current, and if the short circuit is close to the 200amp panel, it will pull the voltage down on one phase significantly as measured at the panel. That voltage drop, along with distorted phase angles seen by the motor(s) can certainly cause a spike in current draw on the unaffected phases. It just happens this current is above some threshold on the 70amp breaker, coupled with what ever even is taking place on the 100amp feeder in its combined amount also takes out the 200amp main.


I am aware this is may be using imagination to some degree; as in general I doubt a 208 volt emergency panel will have many motors or a single large motor, but come real world anything is possible. I have seen blueprints where air compressors for dry type sprinkler systems are placed on the 208 volt emergency panel.


https://www.generalairproducts.com/fire-protection-products/fire-protection-air-compressors.html

 

[K8MHZ]

Bob,

If you do get to watch the cable test crew, please let us know what they were using. I haven't seen a big time cable test crew in over ten years and they were already using ultrasonic TDR voodoo type stuff. Not only could they tell if a cable was bad, but how far down the line the fault was. I found it very interesting. They didn't find a fault, luckily. It was QC on a big MV cable run we pulled at a power plant.

 

[iwire]

I am aware this is may be using imagination to some degree;

IMPO to a very high degree.

 

[iwire]

Bob,

If you do get to watch the cable test crew, please let us know what they were using.

For sure.

My better camera is beside me charging.

 

[mbrooke]

IMPO to a very high degree.

But none the less still worth considering what loads are on the 208 volt emergency panel. When there is no seemingly logical explanation for a breaker tripping that should not be it requires a leap in probable thinking IMO.

 

[kwired]

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.

Where in the world did I even hint at that?

The entire point of the post you quoted was that this is too much money in copper and labor to just guess at things.

That is why a testing company is coming out tonight.



I am mystified why you would think we would hire a testing company and then ignore what they find. :huh:

If the testing company says they are confident the conductors are good the conductors will not be replaced.

If the testing company says they are confident the conductors are bad the conductors will be replaced.

If the testing company says they can't say I am not sure what direction will be taken.

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.

Maybe misunderstood exactly what you meant here. Starts off sounding like you normally would have replaced conductors without finding out what condition they are in, you did mention there is a lot of copper in this instance though. You did mention monitoring - I presume voltage and current, did not mention insulation testing (or I missed it).

 

[K8MHZ]

For sure.

My better camera is beside me charging.

:thumbsup:

New Iphones take amazing pictures, too! I have lots of camera stuff from my days as a wedding photographer, and have a very picky eye when it comes to photos. My daughter's Iphone rivals my Canon EOS gear, and in some cases, blows it out of the water. This is a picture of a wire I found under the dash of her car. The gray wire is 0.5mm, same as 24 AWG. She took this pic with her phone, using light from my flashlight to get the focus. The phone was about 6 inches from the wire. We took the pic because the exposed wire was so small it was nearly invisible to the naked eye.

View attachment 17040

 

[iwire]

Maybe misunderstood exactly what you meant here. Starts off sounding like you normally would have replaced conductors without finding out what condition they are in,

Normally yes, that is what normally means The flip side of that is this must not be normal if we are not doing what we normally would do.




Normally if I had an underground run of 10 AWGs running 150' out to a site pole and the circuit kept tripping I would probably replace the conductors without calling in a testing company. but 2,000' of copper is not the same as 150' of 10 AWG so it is not normal.

 

[ptonsparky]

I can't even imagine setting up a crew to remove and pull that amount of wire in the allotted time.

 

[kwired]

Normally yes, that is what normally means The flip side of that is this must not be normal if we are not doing what we normally would do.




Normally if I had an underground run of 10 AWGs running 150' out to a site pole and the circuit kept tripping I would probably replace the conductors without calling in a testing company. but 2,000' of copper is not the same as 150' of 10 AWG so it is not normal.

Would you put a megohmeter on it before replacing it or calling a testing company?

I don't like to just replace things without some assurance they need replaced. Still get caught doing that once in a while. Replaced a photocell recently without much checking just assuming it was the problem, but it wasn't. Then found out there was a dimmer in the line, and the CFL's in the luminaires of course don't play well with dimmers. A little more thorough investigation the first time, and I likely would have caught that.

 

[iwire]

I can't even imagine setting up a crew to remove and pull that amount of wire in the allotted time.

Lucky we can bring in a lot of guys and as bad as the ATS removal at one end will be bad the other end is very easy, plenty of space to set up reels and the truck can pull up close to drop off.

If anything will slow us it will be the ATS, it has a number of conduits entering the top.

 

[iwire]

Would you put a megohmeter on it before replacing it or calling a testing company?

It depends on what has been happening but yes for sure sometimes. Costs vs time vs need to get on line vs my mood vs the weather conditions vs how mad my wife will be if I get home late etc.

I don't like to just replace things without some assurance they need replaced. Still get caught doing that once in a while.

Its comes with the job. Its always a balancing act with labor costs to be more diligent vs the risk of wasting some wire.

 

[retirede]

Once I had a maintenance electrician call me out to the plant to look at a panel that had multiple breakers that had tripped simultaneously. He couldn't figure out why and neither could I. We later learned that a tow motor hit the beam that the panel was mounted on at the time of trip. That's when I learned that QO breakers can go to the tripped position on a mechanical shock event.


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[mbrooke]

Once I had a maintenance electrician call me out to the plant to look at a panel that had multiple breakers that had tripped simultaneously. He couldn't figure out why and neither could I. We later learned that a tow motor hit the beam that the panel was mounted on at the time of trip. That's when I learned that QO breakers can go to the tripped position on a mechanical shock event.


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Nearly all modern modeled case circuit breakers will trip on a large enough shock event. The magnetic trip function is simply a movable strip of metal, so anything that send it jolting will trip the breaker.

 

[steve66]

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?

I'm thinking that the transformer on the 100 amp breaker trips causes it to trip, and the transformer on the 70 amp breaker causes it to trip. Either one of the, or both together might be enough to trip the main.

They always happen a the same time because everything is switched at the same time. That is, once in a while when the ATS transfers back to normal power, the phasing between the generator and the utility are just right to cause all three breakers to trip. Other times, the phasing between the generator and the utility is closer, and all three breakers hold the load.

There could also a case where one transformer has to dump some current during a transfer back to normal power, and that the main and the other branch breaker are the paths it finds.

But just my WAG.

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.

If the ATS has an in-phase monitor available, turning that on may also help.

Honestly, in this case, with these smaller breakers, I probably wouldn't hesitate to turn up the magnetic settings. It would increase the arc flash some, but I don't see any other real downsides. That's probably your best bet of not having them trip again no matter what is causing this.

By the way, what size are the transformers? Are the breakers properly sized to start with?

 

[Luketrician]

did you test insulation resistance phase to phase & phase to earth ground? I would also want to perform a bridge test, or use a DLRO on them 500s to see what condition they are in. I wouldn't be surprised if those 500s have lost some surface area due to faulting out.


If those 500kcmil feeder cables are faulting phase to phase during wet conditions, I could see that those breakers are just sensitive enough to detect that fault current, and since the fault current is common to the other breakers, I see the fault conditions causing current to surge towards the source of the fault, and in the process tripping out the other breakers.


I think the oversized feeders on the incoming 200amp main are just allowing more fault current to present itself also.


IMHO.

 

[Chamuit]

Power blips?

Power blips?

We had a situation at a site where two breakers fed by the same supply to two different circuits would trip if there was a power loss, upon restoration. The EE in charged surmised that the inrush was causing the breakers to trip simultaneously. Some of the equipment down stream was set to not automatically restart to prevent the inrush exxceeding the breaker capacity.

 

[mach531]

I'll pose a theory....what if the upstream transformer is an ungrounded "floating" wye providing the 480/277V source. Then if the 70a breaker has a ground fault on say 'A' phase and the 100a breaker has a ground fault on 'B' phase you would have a L-L fault that could cause all three breakers to trip.

As for why it happens when it is wet...maybe one of the ground faults is on a downstream 277V outdoor light fixture that is fed from a contactor. So you wouldn't necessarily see the fault with a megger when deenergized.


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