Ground Fault Protection Article 2.30.95

[poweringtech]

Why is it that ground fault is only required for voltage greater than 150 volts to ground?

Is it safe not to have ground fault protection if system voltage is 240Y/139 volts for main disconnect having 1000Amps and above?

Has there been a study on the effect of ground fault for this system voltage?

Do you have refeence material on the explanation of this provision?

Have a great day to everybody

 

[don_resqcapt19]

Re: Ground Fault Protection Article 2.30.95

GFP is required only for systems operating at over 150 volts to ground because the arcing fault tends to self extinguish at each zero crossing on lower voltage systems.
Don

 

[infinity]

Re: Ground Fault Protection Article 2.30.95

if system voltage is 240Y/139 volts

Where would you use this system?

 

[redfish]

Re: Ground Fault Protection Article 2.30.95

if system voltage is 240Y/139 volts

Please explain.

 

[steve66]

Re: Ground Fault Protection Article 2.30.95

The handbook says:

this "was first required in the 1971 code because of the unusually high number of burndowns reported on those types of service."

I'm not exactly sure what a "burndown" is. If they meant a fire, why didn't they just say a fire.

Steve

[ August 19, 2005, 04:09 PM: Message edited by: steve66 ]

 

[charlie b]

Re: Ground Fault Protection Article 2.30.95

I think the "240Y/139" was merely using, as an example, the highest voltage system that the OP could think of, for which the voltage to ground was lower than 150 volts.

 

[charlie b]

Re: Ground Fault Protection Article 2.30.95

Originally posted by steve66:I'm not exactly sure what a "burndown" is. If they meant a fire, why didn't they just say a fire.

Simple. In 1971, the year 1984 was still way in the future. In recognition of this fact, the handbook statement was written in the "newspeak" language of George Orwell's book, "1984."

 

[iwire]

Re: Ground Fault Protection Article 2.30.95

Originally posted by steve66:
I'm not exactly sure what a "burndown" is. If they meant a fire, why didn't they just say a fire.

Steve what I think they mean is that the conductors (buss bars, wire, metal enclosures) just keep melting away without opening the overcurrent device.

I do not think we are talking about a self supporting fire, once the power is cut the burndown stops.

 

[poweringtech]

Re: Ground Fault Protection Article 2.30.95

Thank you very much for your answers.

Steve66
Where can I buy the handbook you are mentioning? What is the title of the handbook?

 

[iwire]

Re: Ground Fault Protection Article 2.30.95

Originally posted by poweringtech:
Do you have the technical explanation why at less than 150 volts to ground arcing ground fault is not a factor? :

Don already posted the reason, first post after your question.

Originally posted by don_resqcapt19:
GFP is required only for systems operating at over 150 volts to ground because the arcing fault tends to self extinguish at each zero crossing on lower voltage systems.
Don

 

[rcwilson]

Re: Ground Fault Protection Article 2.30.95

Maybe melt down or arc down would be a better description. But the end result leaves a lot of smoke and ash so it looks like a fire.(I helped shovel out what was left of a 3200A 480/277 board in a manufacturing plant. Many wheelbarrows full of melted copper, slag and ash.)

480/277 systems have enough voltage to ground to maintain an arc but not enough voltage to make a large breaker or fuse trip in a reasonable amount of time. The arc voltage keeps the fault current below the instantaneous trip of the breaker so the breaker sees the fault as a temporary overload and takes it time in tripping. The resulting energy released in the arc melts the gear to the ground.

Many cases of complete switchboard melt downs led to the ground fault protection requirement for larger services. The ground fault protection measures only ground faults so it does not need to be set above the maximum load current like normal over current protection. It can trip quickly on ground faults, arcing or not.

As stated in other posts, lower voltages to ground can't maintain the arc so the breaker trips or there is a lot less damage.