# 1000 amp. 480 V breaker tripped



## Davethewave (Jan 6, 2012)

I do service work for the owner of a industrial complex. One of the tenants had their own electrician doing some TI's and tripped the 1000 Amp main by shorting a 277 volt 400 watt MH. It dropped the service out to the "Got Net" server room. He told the owner that the 20 Amp. breaker was defective and needed to be replaced. I contended that the trip was a result of a ground fault and not an excessive load which could affect any breaker on the line. The debate is on....


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## micromind (Aug 11, 2007)

I'd be willing to bet that even right after the implementation of a coordination study, if a 20 amp branch circuit were to become solidly faulted to ground, the ground fault on the feeder (or main) breaker would trip before the 20 would.


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## BBQ (Nov 16, 2010)

micromind said:


> I'd be willing to bet that even right after the implementation of a coordination study, if a 20 amp branch circuit were to become solidly faulted to ground, the ground fault on the feeder (or main) breaker would trip before the 20 would.


I would take your bet, I get involved in this type of thing fairly often and the problems seem to stop as soon as the study is done and implemented. 

Typically the breakers are shipped with all the settings at their lowest current and least delay times. Often no one touches the settings because no study has been done so the problems begin. 

The delayed pick up time added after the study should let the small breaker clear first. At least that has been my experiance with this issue.


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## Zog (Apr 15, 2009)

Davethewave said:


> I do service work for the owner of a industrial complex. One of the tenants had their own electrician doing some TI's and tripped the 1000 Amp main by shorting a 277 volt 400 watt MH. It dropped the service out to the "Got Net" server room. He told the owner that the 20 Amp. breaker was defective and needed to be replaced. I contended that the trip was a result of a ground fault and not an excessive load which could affect any breaker on the line. The debate is on....


Well you can have the 20A breaker tested just to be sure but I am thinking you are likely right, I bet the main is the only breaker with GFP.


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## glen1971 (Oct 10, 2012)

BBQ said:


> I would take your bet, I get involved in this type of thing fairly often and the problems seem to stop as soon as the study is done and implemented.
> 
> Typically the breakers are shipped with all the settings at their lowest current and least delay times. Often no one touches the settings because no study has been done so the problems begin.
> 
> The delayed pick up time added after the study should let the small breaker clear first. At least that has been my experiance with this issue.


I had a tough time convincing a plant manager of that. He thought they all came preset for their installation. I tried explaining that they will, if provided with the settings, but adjusting to anything but the minimum is liability for the manufacturer. He wouldn't let me adjust them, until the Cutler Hammer service rep was on site, as he thought it was their issue. The rep came in and made a couple of turns and away they went. I found out later that as a "cost savings measure" they didn't get a coordination study done. Wonder how that worked out for them as they stood in the plant in the dark for 2 hours?


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## Zog (Apr 15, 2009)

glen1971 said:


> I had a tough time convincing a plant manager of that. He thought they all came preset for their installation. I tried explaining that they will, if provided with the settings, but adjusting to anything but the minimum is liability for the manufacturer. He wouldn't let me adjust them, until the Cutler Hammer service rep was on site, as he thought it was their issue. The rep came in and made a couple of turns and away they went. I found out later that as a "cost savings measure" they didn't get a coordination study done. Wonder how that worked out for them as they stood in the plant in the dark for 2 hours?


That happens often, nice cost savings. An even worse "solution" is to dial them all the way up.


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## Big John (May 23, 2010)

glen1971 said:


> ...Wonder how that worked out for them as they stood in the plant in the dark for 2 hours?


 Even with the lights back on, managers like that are always in the dark. :whistling2:

-John


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## Control Freak (Mar 8, 2008)

A couple of years ago when I was an apprentice my journeyman was landing a lighting circuit on a 15 or 20 amp breaker. He skinned the wire and it shorted to the detail. The fault bypassed the main 200 amp breaker at that particular panel and blew the 400 amp fuse at the bus plug. For some reason it happens with 277/480 more often than 120/208. That's strictly from experience and it could have nothing to do with voltage. This is due to the interrupting ratings of the breaker being set incorrectly. The ratings should be lower downstream in order to trip at the main breaker as opposed the distribution. before the


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## Zog (Apr 15, 2009)

Control Freak said:


> A couple of years ago when I was an apprentice my journeyman was landing a lighting circuit on a 15 or 20 amp breaker. He skinned the wire and it shorted to the detail. The fault bypassed the main 200 amp breaker at that particular panel and blew the 400 amp fuse at the bus plug. For some reason it happens with 277/480 more often than 120/208. That's strictly from experience and it could have nothing to do with voltage. This is due to the interrupting ratings of the breaker being set incorrectly. The ratings should be lower downstream in order to trip at the main breaker as opposed the distribution. before the


You can't adjust interuption ratings of a breaker. :blink:


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## micromind (Aug 11, 2007)

Zog said:


> You can't adjust interuption ratings of a breaker. :blink:


True, the AIC rating is a design function built in to the breaker at the time of manufacture and is not adjustable.

I think he meant the instantaneous trip current and time.


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## Meadow (Jan 14, 2011)

GFP aside, If the 20amp breaker was faulty wouldnt the 12 guage burn up or get really hot?


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## Spark Master (Jul 3, 2012)

So who's going to reset a 1000amp 480 V breaker ?? Especially after a dead short. You would not see me doing that task. Not even in a moon suit.


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## nolabama (Oct 3, 2007)

Spark Master said:


> So who's going to reset a 1000amp 480 V breaker ?? Especially after a dead short. You would not see me doing that task. Not even in a moon suit.


I would do it in a moon suit over my nomex wirh a six foot 2x4. Lol.


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## Hippie (May 12, 2011)

Spark Master said:


> So who's going to reset a 1000amp 480 V breaker ?? Especially after a dead short. You would not see me doing that task. Not even in a moon suit.


At my old job we had a 800A breaker on a chiller that would trip every so often, mounted open in a cabinet. I reset it many times with nothing but a piece of 2x4.. I didn't like doing it at the time but thinking about it now I can't believe I was that dumb. It was probably 30 years old and usually took 5-10 tries to get it to reset


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## Big John (May 23, 2010)

Spark Master said:


> So who's going to reset a 1000amp 480 V breaker ?? Especially after a dead short. You would not see me doing that task. Not even in a moon suit.


 I had an emergency call where a guy had closed a 15kV breaker into a fault multiple times. It was only after, and I quote: "Fire started shooting out of the vents" on the switchgear, that he decided to stop and call somebody. :wallbash: :wallbash:

-John


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## FastFokker (Sep 18, 2012)

Spark Master said:


> So who's going to reset a 1000amp 480 V breaker ?? Especially after a dead short. You would not see me doing that task. Not even in a moon suit.


There's electricians on this website who would do it in their underwear while smoking a cigarette and standing in gasoline.


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## Speedlimit190 (Apr 29, 2012)

There's electricians on this website who would do it in their underwear while smoking a cigarette and standing in gasoline.[/QUOTE]

Fix the fault, strip down to your undies so the potential arc flash doesn't brand you with your shops logo off of your shirt your life, light your cancer stick and throw the switch. Another day in the life of an electrician. Give me something hard to do.


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## Zog (Apr 15, 2009)

I have robots that do that for me.


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## Vintage Sounds (Oct 23, 2009)

Speedlimit190 said:


> Fix the fault, strip down to your undies so the potential arc flash doesn't brand you with your shops logo off of your shirt your life, light your cancer stick and throw the switch. Another day in the life of an electrician. Give me something hard to do.


Those undies better be natural cotton


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## frenchelectrican (Mar 15, 2007)

Zog said:


> I have robots that do that for me.


I used Chicken switch from time to time.

Merci,
Marc


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## Spark Master (Jul 3, 2012)

During the hurricane outage, I was backfeeding my panel. So I had the 200 amp main off. *The main hasn't been touched in 25 years.*

When it came time to turn the main back on, 3am, I actually put on 2 layers of clothes. hooded sweat shirt, looked the other way, with my back towards the panel. with my hand behind my back, I put the main back on.

I unloaded the whole panel first. Then I slowly turned all the breakers back on. But I have seen conflicting information about turning on mains loaded or unloaded. I like the unloaded method to avoid a surge. But I understand there is more energy to flash over if you unload the panel.


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## Zog (Apr 15, 2009)

frenchelectrican said:


> I used Chicken switch from time to time.
> 
> Merci,
> Marc


One trick pony, only works on pistol grips. I have over 200 different versions to remotely (Wireless) operate anything.


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## Zog (Apr 15, 2009)

Spark Master said:


> But I understand there is more energy to flash over if you unload the panel.


Um, no. In fact, if you have motors, the motor contribution would add to the available fault current so it would be more energy on a loaded panel in that case.


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## Spark Master (Jul 3, 2012)

Zog said:


> Um, no. In fact, if you have motors, the motor contribution would add to the available fault current so it would be more energy on a loaded panel in that case.


 
So then my thinking is correct, to unload the entire panel, before touching the main.


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## Zog (Apr 15, 2009)

Spark Master said:


> So then my thinking is correct, to unload the entire panel, before touching the main.


Yes, that is considered the best practice.


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## nolabama (Oct 3, 2007)

Spark Master said:


> So then my thinking is correct, to unload the entire panel, before touching the main.


I do that. I have had a contractor laugh at me for it too


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