# 277 voltage ?



## Voltech (Nov 30, 2009)

Saw a guy hooked up a 277v light, he pinched the switch leg. Sparks, banging and popping followed. It never threw the breaker thought. Cut the wire and melted the metal where the pinch was. Why?

20 amp BC with no more than 5 amps being used, about 100 ft from Panel


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## Murphy (Dec 10, 2009)

Voltech said:


> Saw a guy hooked up a 277v light, he pinched the switch leg. Sparks, banging and popping followed. It never threw the breaker thought. Cut the wire and melted the metal where the pinch was. Why?
> 
> 20 amp BC with no more than 5 amps being used, about 100 ft from Panel


 
good question....breaker malfunction? i have no clue.. if it was grounded to create sparks.. ovbiously there was a lot of current drawing..


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## Wingnut (Jan 31, 2010)

what manufacture and type of breaker?


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## RIVETER (Sep 26, 2009)

Voltech said:


> Saw a guy hooked up a 277v light, he pinched the switch leg. Sparks, banging and popping followed. It never threw the breaker thought. Cut the wire and melted the metal where the pinch was. Why?
> 
> 20 amp BC with no more than 5 amps being used, about 100 ft from Panel


The point of the pinch became less conductive, actually very resistive. The current flowing caused a lot of heat at the junction and the copper eventually melted.:thumbsup:


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## Voltech (Nov 30, 2009)

Wingnut said:


> what manufacture and type of breaker?



GE bolt in. This panel feeds the entire floor. 250 mcm feeding a 250 amp 480y/277v panel. 1 3p 60amp feeding a 45 Kva Xformer and 110 amp 3p feeding 75 KVA Xformer. With about 10 lighting 20 amp 277 circuits.


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## Bob Badger (Apr 19, 2009)

A 277 volt circuit provides much more power to a short and commonly will blow out a lot of metal before tripping a breaker.


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## Voltech (Nov 30, 2009)

Bob Badger said:


> A 277 volt circuit provides much more power to a short and commonly will blow out a lot of metal before tripping a breaker.


Makes sense, it sounded like a welder, but didnt weld, it was cutting and blowing


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## Bob Badger (Apr 19, 2009)

Voltech said:


> Makes sense, it sounded like a welder, but didnt weld, it was cutting and blowing


Services (230.95) and feeders (215.10) with a voltage exceeding 150 volts to ground and larger than 1000 amps additional ground fault protection is required because in those high capacity circuits a normal breaker or fuse might not ever blow, the conductors would just keep melting the enclosures and raceways.


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## micromind (Aug 11, 2007)

In my experience, if there is ground fault on the main, the main will usually trip before the branch circuit breaker during a short to ground. 

Rob


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## raider1 (Jan 22, 2007)

micromind said:


> In my experience, if there is ground fault on the main, the main will usually trip before the branch circuit breaker during a short to ground.
> 
> Rob


Are you sure the ground fault protection on the main was properly set?

Chris


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## 480sparky (Sep 20, 2007)

Not a bolted fault, but you created a 'fusible link'. Enough resistance to arc & spark, but not enough current flow long enough for the breaker to react. Once things melted, current flow was reduced and the breaker saw it all as just a short surge in current use.


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## BuzzKill (Oct 27, 2008)

480sparky said:


> Not a bolted fault, but you created a 'fusible link'. Enough resistance to arc & spark, but not enough current flow long enough for the breaker to react. Once things melted, current flow was reduced and the breaker saw it all as just a short surge in current use.


best description


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## moman (Apr 15, 2010)

micromind said:


> In my experience, if there is ground fault on the main, the main will usually trip before the branch circuit breaker during a short to ground.
> 
> Rob


I once pinched a wire on a 277v circuit and it dumped the main. Thankfully the building was empty.:whistling2:


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## SparkYZ (Jan 20, 2010)

moman said:


> I once pinched a wire on a 277v circuit and it dumped the main. Thankfully the building was empty.:whistling2:


I once put on a gutter cover and shot a screw thru a 277V lighting circuit. Some wiseguy decided to run the wires right in the corner of the gutter, where it was BEGGING to get hit by a screw...Well, I did...
It shut down ALL of the lighting panels in a WALMART at 2 AM. Tripped the main because of the ground fault protection.
The store was dark, the parking lot was dark, emergency lights were on...

Man...was I embarassed...


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## BuzzKill (Oct 27, 2008)

SparkYZ said:


> I once put on a gutter cover and shot a screw thru a 277V lighting circuit. Some wiseguy decided to run the wires right in the corner of the gutter, where it was BEGGING to get hit by a screw...Well, I did...
> It shut down ALL of the lighting panels in a WALMART at 2 AM. Tripped the main because of the ground fault protection.
> The store was dark, the parking lot was dark, emergency lights were on...
> 
> Man...was I embarassed...


Surely there is a way around this instead of tripping the main....


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## brian john (Mar 11, 2007)

480/277 VAC distribution systems do not respond to arcing faults the same way a 208/120 VAC system does, the peak of the sine wave is sufficient to result in an arc through a high impedance connection this allows the arc to re-establish itself, were as in a 208/120 VAC system the arc will go out.

As for tripping the main this is why GFP systems are installed, the 480/277 VAC arcing ground faults are low amperage (the is not a bolted fault the fault the current is through the arc) and will not open a fuse or circuit breaker (per the NEC 1000 amps or higher, engineering I have no idea of the numbers). Nuisance tripping the GFP this is most likely a result of improper setup, testing and usually no coordination study. Electrical engineers conveniently overlook the coordination study.

While it is not recommend that you adjust a GFP system, in reality electricians do it regularly. Myself we recommend leaving the system set on minimum to avoid liability, till such time as a coordination study is completed and we can adjust and test the system.

It is next to impossible to completely coordinate a GFP system due to the maximum setting of 1200 amps at 1-second. But it is possible to minimize nuisance tripping GFP systems by adjusting the settings to 400 amps or higher and .1 second or higher. I figure 90-95% of the OCPs in a building are 20 and 30 amp circuit breakers, setting at 400 amps 1. seconds gets you outside the curve for most of these OCPs. 

As for the term nuisance tripping the GFP is IMO not nuisance tripping it is doing it job, the engineer and/or knuckle head electrician working hot are the nuisance.


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## Voltech (Nov 30, 2009)

SparkYZ said:


> I once put on a gutter cover and shot a screw thru a 277V lighting circuit. Some wiseguy decided to run the wires right in the corner of the gutter, where it was BEGGING to get hit by a screw...Well, I did...
> It shut down ALL of the lighting panels in a WALMART at 2 AM. Tripped the main because of the ground fault protection.
> The store was dark, the parking lot was dark, emergency lights were on...
> 
> Man...was I embarassed...




Yes sir, this is apart of our free safety check. Looks like everything is working properly :whistling2::whistling2:


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## Skipp (May 23, 2010)

Voltech said:


> GE bolt in. This panel feeds the entire floor. 250 mcm feeding a 250 amp 480y/277v panel. 1 3p 60amp feeding a 45 Kva Xformer and 110 amp 3p feeding 75 KVA Xformer. With about 10 lighting 20 amp 277 circuits.


 It may be of interest to you, that I had the same problem with GE bolt ons. Brand new panel breakers and all wiring at a school. The breakers in this panel would not at all. One guy actually dead shorted some of the load circuit wires to prove the point. Although this was a 120/208 system. It was brand new GE A-series panel with bolt ons w/THQBs. I watched a grounded circuit (on purpose) completely melt wire nut, catch fire, and melt insulation. The breaker never responded. 277 or not your breaker should have tripped in miliseconds. 
For the record, I don't approve of shorting wires to test breakers. But it was there electrical equipment. I was just an observer to the demostration.


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## brian john (Mar 11, 2007)

Skipp said:


> It may be of interest to you, that I had the same problem with GE bolt ons. Brand new panel breakers and all wiring at a school. The breakers in this panel would not at all. One guy actually dead shorted some of the load circuit wires to prove the point. Although this was a 120/208 system. It was brand new GE A-series panel with bolt ons w/THQBs. I watched a grounded circuit (on purpose) completely melt wire nut, catch fire, and melt insulation. The breaker never responded. 277 or not your breaker should have tripped in miliseconds.
> For the record, I don't approve of shorting wires to test breakers. But it was there electrical equipment. I was just an observer to the demostration.


There could be several issues going on here, biggest one is dead shorting anything.

One CB bad OK you have a bad CB multiple CB's and there is an issue you guys are over looking.

Especially if the system has GFP and the GFP did not operate at some point.

Second I would have GE service out there the next day.

What was the final outcome for this issue?


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## Zog (Apr 15, 2009)

Skipp said:


> It was brand new GE A-series panel with bolt ons w/THQBs. I watched a grounded circuit (on purpose) completely melt wire nut, catch fire, and melt insulation. The breaker never responded. 277 or not your breaker should have tripped in miliseconds.


Why would you think the breaker would trip on a ground fault?


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## Skipp (May 23, 2010)

Zog said:


> Why would you think the breaker would trip on a ground fault?


 If a hot wire is wire nutted right to a grounded or grounding conductor, then yes I expect a circuit breaker to trip. Am I expecting too much for a CB to do what it was intended for?


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## brian john (Mar 11, 2007)

Skipp said:


> If a hot wire is wire nutted right to a grounded or grounding conductor, then yes I expect a circuit breaker to trip. Am I expecting too much for a CB to do what it was intended for?


Depending on how the GFP is set maybe maybe not,
Depending on proper installation of grounds maybe maybe not.

What was the final outcome of all this?


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## Zog (Apr 15, 2009)

Skipp said:


> If a hot wire is wire nutted right to a grounded or grounding conductor, then yes I expect a circuit breaker to trip. Am I expecting too much for a CB to do what it was intended for?


That breaker does not have GF protection.


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## Bkessler (Feb 14, 2007)

After I tripped a 1200 amp main in a medical building, I dont' short out wires to locate the breaker. That was the last time I did that and that was over 10 years ago, now every once in a while I will short out a couple wires that I am pretty sure they are all ready dead. Just to be sure.

I remember once turning on a 277 switch where the switch-leg was directly wired to the neutral in the fixture. (the gray looked black when it was spliced by an old timer), when I turned the switch on it was like an m80 was in that switch-box, boy was that loud and it blew the switch apart.


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## brian john (Mar 11, 2007)

Zog said:


> That breaker does not have GF protection.


 
But assuming all components of the distribution system are properly installed, and the main GFP is set high enough that the 20 amp instantaneous has time to operate this should trip the CB.


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## Bob Badger (Apr 19, 2009)

Zog said:


> That breaker does not have GF protection.


Yet many breakers without GFP will open when a ground fault happens, but you know that so maybe you can explain the point you are trying to make.


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## Zog (Apr 15, 2009)

Bob Badger said:


> Yet many breakers without GFP will open when a ground fault happens, but you know that so maybe you can explain the point you are trying to make.


Maybe, maybe not. Ground faults can be either a low impedance type, developing a significant amount of electrical energy, or as an arcing type fault with little total energy consumed. The common breaker is not designed or calibrated to respond to arcing type shorts to ground. 

Circuit breakers typically will respond to a short to ground that is of the low impedance type however the impedence that exists in the system will make the GF current much lower than a short circuit would be. Usually this lower current will not be high enough to cause an INST trip, but after some period of time will likely cause a LT (Overload) trip to occur, but by then the damage is usually already done. 

This is why facilities that have GF protection on thier mains, but not on thier feeders, experience mains tripping from a GF.

The "point I am trying to make" Bob, is that the post I was quoting stated that the breaker without GFP was "intended" to trip on a GF, which it is not.


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## Bob Badger (Apr 19, 2009)

Zog said:


> The "point I am trying to make" Bob, is that the post I was quoting stated that the breaker without GFP was "intended" to trip on a GF, which it is not.



Are you saying a common single pole 277 volt 20 amp breaker supplying a lighting circuit is not intended to provide protection against ground faults?

If that is your point I will have to disagree with you on that. You really are stuck on the big work aren't you?


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## Zog (Apr 15, 2009)

Bob Badger said:


> Are you saying a common single pole 277 volt 20 amp breaker supplying a lighting circuit is not intended to provide protection against ground faults?
> 
> If that is your point I will have to disagree with you on that. You really are stuck on the big work aren't you?


No, I am talking about a single pole 277V 20A breaker, I already offered the explanation on why they are ineffective, and that is the reason GF modules are available as an accessory in residential and commercaial LV applications, just no one buys them because they don't understand the need and do everything possible to cut costs.

Now if you actually read my post before bashing me as usual you would have seen that I stated that it would eventually trip, but as an overload function so the time delay would be signifigant due to the high impedance, if it was an arcing fault to ground the breaker would likely never trip.


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## Skipp (May 23, 2010)

brian john said:


> Depending on how the GFP is set maybe maybe not,
> Depending on proper installation of grounds maybe maybe not.
> 
> What was the final outcome of all this?


 The finall outcome was they did nothing. They just said as long as the circuits don't overload we will be fine! That was in Oct. 2006 and to this day they have done nothing to address the problem. The work was all done by a union contractor. Everything was knew and clean looking. Dedicated Neutrals for every circuit, short runs, tight connections..etc.


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## Bob Badger (Apr 19, 2009)

Zog said:


> No, I am talking about a single pole 277V 20A breaker, I already offered the explanation on why they are ineffective, and that is the reason GF modules are available as an accessory in residential and commercaial LV applications, just no one buys them because they don't understand the need and do everything possible to cut costs.
> 
> Now if you actually read my post before bashing me as usual you would have seen that I stated that it would eventually trip, but as an overload function so the time delay would be signifigant due to the high impedance, if it was an arcing fault to ground the breaker would likely never trip.


Most ground fault events I have witnessed or had to service trip the breaker immediately as the current is well into the instantaneous trip region of the breaker and does not have to wait for a thermal trip.

Does it go that way every time? Nope.

But I still feel it is wrong to say a standard breaker does not provide ground fault protection. It provides just as much ground fault protection as it provided short circuit protection. (Remember we are talking a single phase 277 volt circuit)


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## Bob Badger (Apr 19, 2009)

Lets look back at how the conversation went.



Skipp said:


> It was brand new GE A-series panel with bolt ons w/THQBs. *I watched a grounded circuit (on purpose) *completely melt wire nut, catch fire, and melt insulation. The breaker never responded. 277 or not your breaker should have tripped in miliseconds.





Zog said:


> Why would you think the breaker would trip on a ground fault?





Skipp said:


> *If a hot wire is wire nutted right to a grounded or grounding conductor,* then yes I expect a circuit breaker to trip. Am I expecting too much for a CB to do what it was intended for?





Zog said:


> That breaker does not have GF protection.



Electricians and the NEC expect breakers to protect against ground faults, they are required to.


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## Mike_586 (Mar 24, 2009)

Bob Badger said:


> Electricians and the NEC expect breakers to protect against ground faults, they are required to.


Non-GFP breakers are required to, by design and the NEC to provide GFP protection? Show me one manufacturer spec, UL spec or one NEC article that says that.


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## Bob Badger (Apr 19, 2009)

Mike_586 said:


> Non-GFP breakers are required to, by design and the NEC to provide GFP protection?


Gee, I hope so, and fuses as well. :laughing:

For example Table 430.52 speaks of the requirements for short circuit and ground fault protection of motor conductors.

What kind of ground fault protection do we often use to meet those requirements? Standard fuses and inverse time breakers.


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## Mike_586 (Mar 24, 2009)

OK I glanced at the NEC a little and I'm still a little confused by it. The only ground fault stuff I ever have to worry about is either GFCI's, from the little Class A type up to the bigger adjustable types, or ground fault sensing on high impedance grounded systems. For us the rest is grounding and bonding.

I really don't spend much time looking at the NEC since its only a mild curiosity for me, but it seems to me that what you guys are calling ground fault protection is what we just call plain old grounding and bonding. Do your grounding and bonding right and the current has a low impedance path back to the source to facilitate the proper operation of the over current device. 

I was thinking along the lines of GFCI protection and wondering how the hell you could get that from a standard breaker/fuse.


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## Bob Badger (Apr 19, 2009)

Mike_586 said:


> OK I glanced at the NEC a little and I'm still a little confused by it.


That is normal, even those of us who work with it all the time are confused by it. 





> The only ground fault stuff I ever have to worry about is either GFCI's, from the little Class A type up to the bigger adjustable types, or ground fault sensing on high impedance grounded systems.


I total understand Class As, GFP for bigger stuff, I have never worked with the high impedance systems.



> For us the rest is grounding and bonding.


Of course grounding and bonding are of utmost importance but as you know, neither of those things will actually stop the flow of current, only redirect it.

With proper bonding standard breakers and fuse will open quickly (most times) under ground-fault conditions on branch circuits and smaller feeders.




> I was thinking along the lines of GFCI protection and wondering how the hell you could get that from a standard breaker/fuse.


Without a doubt if we open a standard thermal magnetic breaker there will be no component that we can point to and say 'that part is dedicated to GFP' but assuming a grounded system the instantaneous trip component can and will provide as much ground fualt protection as it does line to line fault protection.


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## Voltech (Nov 30, 2009)

I was working some lighting one time and the SW was grounded, so when I hit the breaker I could hear the lines jumping in the raceway. Still no breaker tripped. I was on the other side of the building ao I turned it right off. What causes those line to jump?

20 amp 277v #10 (because of Voltage drop)


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## Zog (Apr 15, 2009)

Bob Badger said:


> Without a doubt if we open a standard thermal magnetic breaker there will be no component that we can point to and say 'that part is dedicated to GFP' but assuming a grounded system the instantaneous trip component can and will provide as much ground fualt protection as it does line to line fault protection.


No it will not due to the relitively high impendance of the GF compared to the short circuit, the current level will be much lower (10%-30%) and not trip the magnetic element. That is why there are specific versions of most MCCB's designed to protect from GF's per UL 1053 and CSA C22.2 No. 144-M91 standards.


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