1600a Main Tripping

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TRMElectricianJourneyman

TRMElectricianJourneyman

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Oregon
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Electrician
??? I have a 1600a main tripping. I was able to narrow down the source to a specific panel, but the customer stopped further investigation until they close for the day.
This is my question;;;
Why is the main service tripping? It goes from a 480v/3P 1600a to a 200a fused switch to a main breaker 200a, down to the branch circuit breakers. Without being able to isolate and test, I’m curious what other people think might be happening? I’m guessing it’s the 200a fused switch, but when it trips, the noise(conduit rattling) is coming from the branch off the 200a main breaker panel.
 
augie47 said:
Likely there was not a coordination study on the system and a ground-fault downstream is causing the 1600 amp GF protectiion to trip.
Depending on the settings on your breaker it could be on a small branch circuit.
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Why wouldn’t the main breaker in the sub panel trip first? I just turned out 3 yrs ago and obviously haven’t seen it all. This is a new one for me! What would be the best way to find the source of the ground fault? I’m going in tonight to investigate further.
This is at a Home Depot that’s been here for 20+ years.
Attached is a pic of the 1600a breaker.
 

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I agree with Gus, and will take it a step further. If a short circuit occurs at a 120 volt outlet, you are going to see a fault current in the hundreds, if not thousands of amps. That current will be flowing through the 1600 amp main breaker, the 200 amp fused switch, the 200 amp panel's main breaker, and the 20 amp branch circuit breaker. All of these devices will experience the fault current and every one will react by starting to activate its trip (or melt) mechanism. Which one will "win the race"? Unless the design accounts for fault coordination, any of the devices (including the 1600 amp main breaker) could be the one that opens the circuit first.
 
That 1600 amp main breaker has the ability to have its trip characteristics adjusted. This could cause it to delay its own trip mechanism so as to allow a device further downstream to trip first. An electrician can make the trip adjustment, but I believe that an engineer needs to determine what adjustment should be made. That is what a fault coordination study does for you. It is not cheap, nor can it be done quickly.

If the study and resulting adjustments are done right, the device closest to the fault point will trip first, minimizing the areas that lose power during the event. If they are done wrong, the tripping mechanisms of all overcurrent devices might not react in time to prevent the fault from starting a fire.

None of what I have described will help you find the culprit. But I hope it will assuage your concerns that the electrical distribution system is misbehaving.
 
charlie b said:
I agree with Gus, and will take it a step further. If a short circuit occurs at a 120 volt outlet, you are going to see a fault current in the hundreds, if not thousands of amps. That current will be flowing through the 1600 amp main breaker, the 200 amp fused switch, the 200 amp panel's main breaker, and the 20 amp branch circuit breaker. All of these devices will experience the fault current and every one will react by starting to activate its trip (or melt) mechanism. Which one will "win the race"? Unless the design accounts for fault coordination, any of the devices (including the 1600 amp main breaker) could be the one that opens the circuit first.
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That definitely sounds like the issue. I’m going to take a closer look tonight. I’m hoping I can isolate it down to the branch circuit. Thank you for the feedback!!!
 
I’m in agreement with others! I seen a ground fault on a 20 amp branch circuit trip the 1200 amp Ground Fault at the main while the 20 amp breaker remained on at a school I worked at. Worker was installing a new garage door opener and drilled into a conduit with a 20 amp breaker That fed the shop lights! It took out the entire building! When I realized what he had done, I turned off the 20 amp circuit feeding the lights and reset the 1200 amp main to get the rest of the building back on. Had to replace damaged conduit and install new conductors for branch circuit!
 
Turn off the individual branch circuit breakers in the panel you believe to be the source. Turn on individually until you can verify Wich breaker/circuit is faulted.

Sent from my SM-S906U using Tapatalk
 
With the orange box, it’s usually either parking lot lights, garden center lights or a rtu. Which panel did you narrow it down to? HA? HD? If it’s HA, it’s probably parking lot lights. If HD, it’s probably garden center lights. Sometimes there is an RTU out of one of those panels, usually office package. Since it’s winter, could be a bad second stage heat strip if the store has electric heat.
 
jim dungar said:
But if there is only GF protection at the main, you nay always experience unintended tripping.
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I agree and has always been a mystery to me why owners/designers do this just to save a few $. I've got enough miles on me that I've seen this many times. It seems to me that just one incident with an unintended main trip in most commercial settings that the cost of down time/loss of revenue would more than pay to use multi level GFPE.
 
hillbilly1 said:
With the orange box, it’s usually either parking lot lights, garden center lights or a rtu. Which panel did you narrow it down to? HA? HD? If it’s HA, it’s probably parking lot lights. If HD, it’s probably garden center lights. Sometimes there is an RTU out of one of those panels, usually office package. Since it’s winter, could be a bad second stage heat strip if the store has electric heat.
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I think it’s the garden center lights. There’s also the battery chargers on this panel, but all of those appear fine.
 
texie said:
I agree and has always been a mystery to me why owners/designers do this just to save a few $. I've got enough miles on me that I've seen this many times. It seems to me that just one incident with an unintended main trip in most commercial settings that the cost of down time/loss of revenue would more than pay to use multi level GFPE.
Click to expand...
Home Depot gets around the ground fault requirements on many of their stores by splitting the service into two mains.
 
It was the garden center! I have to come back with a lift, but we were able to narrow it down to a branch circuit feeding the pole lights. They appear to be newer LEDs. We’ve been getting a ton of rain, ice and wind in the last few weeks. I assume it found its way into a fixture and is creating a ground fault.
It’s still wild to me that it would trip the 1600a main before the 20a branch!!
 
Can you take a close-up picture of the adjustable trip settings on the main.
 
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