Main Breaker Trips

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Arce2ee

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I have a building with two 3000A services with 3000A main breakers. Everytime this building loses utility power the main breakers trip. In one instance the breakers were reset before the utility was restored and they tripped again when the utility was restored. What could be causing these to trip?
 
I saw this one time: The main breaker had a "phase loss detector" installed. The problem was that the detector could not distinguish between the loss of one phase and a power outage in which all phases were lost, so after every power interruption the Main Breaker would need to be re-set.
 
Arce2ee said:
I have a building with two 3000A services with 3000A main breakers. Everytime this building loses utility power the main breakers trip. In one instance the breakers were reset before the utility was restored and they tripped again when the utility was restored. What could be causing these to trip?
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Undervoltage relays (27 device) very common on the type of system you have.
 
haskindm said:
I saw this one time: The main breaker had a "phase loss detector" installed. The problem was that the detector could not distinguish between the loss of one phase and a power outage in which all phases were lost, so after every power interruption the Main Breaker would need to be re-set.
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This is a not un-common situation. There are "special" undervoltage relays that will not trip on a loss of all three phases. I have used some from both Time-Mark and Taylor.
 
If there are enough motor, lighting, and other loads all coming on at the same time upon intial restoration of power, it is possible that the trip levels of the main breaker are not able to handle the inrush current. I've seen that, and replacement or rehab of the breaker was the fix, they seem to tend to drift out of calibration sometimes.
 
macmikeman said:
If there are enough motor, lighting, and other loads all coming on at the same time upon intial restoration of power, it is possible that the trip levels of the main breaker are not able to handle the inrush current. I've seen that, and replacement or rehab of the breaker was the fix, they seem to tend to drift out of calibration sometimes.
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Yes, I should have added that (if the power had been off for some time and the temperature in the building had increased to the point that all of the HVAC units would try to start simultaneously) we needed to turn off the individual breakers for the large HVAC loads before closing the main breaker or it would trip off when all of those items tried to start at once.
 
On a related note, anybody that resets a breaker this big without knowing already the exact reason that it tripped off needs their head examined. I can't stress enough how hazardous this potentially is, at least to equipment and maybe yourself. You won't catch me resetting a 3000A breaker until I've got pinned down exactly why it tripped. Not in a million years.
 
The breaker is tripping on the loss of power.

Arce2ee said:
Everytime this building loses utility power the main breakers trip. In one instance the breakers were reset before the utility was restored and they tripped again when the utility was restored.
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It seems to me zog is onto it. :)


zog said:
Undervoltage relays (27 device) very common on the type of system you have.
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mdshunk said:
Wouldn't matter a hill of beans to me. I still wouldn't reset it until I opened up the door and saw the 27 accessory with my own two eyes.
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That was not really what I was getting at, some of the posters where focusing on the breaker tripping because of inrush currents and seem to have missed the fact it was tripping more times when the utility failed. :)
 
iwire said:
That was not really what I was getting at, some of the posters where focusing on the breaker tripping because of inrush currents and seem to have missed the fact it was tripping more times when the utility failed. :)
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I see, said the blind man.
 
haskindm said:
Yes, I should have added that (if the power had been off for some time and the temperature in the building had increased to the point that all of the HVAC units would try to start simultaneously) we needed to turn off the individual breakers for the large HVAC loads before closing the main breaker or it would trip off when all of those items tried to start at once.
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I have often wondered how the power company manages this in the middle of the summer. Maybe they send guys out in trucks to open various branches, depending on how wide the outage is.

Maybe they even have remotely-operable switches for such occasions, and maybe they even have an automated process for cascading restorations. It boggles the mind, doesn't it? Wow.
 
Some of the reclosers are pretty smart. They can tell some guy 100's of miles away what the nature of the problem was. After storms, they do drive the lines to make a visual check.
 
I have seen older gear in high rises with the phase loss moniter tied to a shunt trip mechanisim, It protected the three phase equiptment from single phasing for a long period of time. Usually when the power company drops power, its from a single phase that was lost due to an accident or tree limb, then later a recloser down the line would open all phases. This usually takes long enough for the phase loss relay to trip and open the main. The delay setting can be very short.
 
Time Mark and Taylor Phase Guard make several models with varying time delays and as noted some have features that only trip on single phase and/or phase unbalance. Buzz Taylor will custom make a phase loss relay with what ever time delay you want...BUT, you should protect you downstream equipment.

NEVER close a switch unless you know why it tripped.
 
I agree with Marc and Brian. I won't close a 15 amp breaker unless I know why it tripped much less a 3ka breaker. I saw a 100 amp breaker blow once. I can't imagine a 3000 amp breaker exploding. I'm guessing all the PPE in world would not save your but.
 
I remember about 15 years ago an "Electrician" in Atlanta, decided to replace a 200 amp 480 volt fuse for a lighting panel in a high rise, not only did he not check to see what blew the fuse, he decided to replace it live. He paid for that mistake with his life. It blew him across the room and thru the door.
 
mdshunk said:
Wouldn't matter a hill of beans to me. I still wouldn't reset it until I opened up the door and saw the 27 accessory with my own two eyes.
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That wouldnt be in the door, it would be panel mounted above the breaker or off to the side.
 
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