request for info

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For the personal safety GFIs, according to UL, the trip time formula is
T = (20/I)^1.43.

For GFIs other than those that protect people, those that trip at higher currents, does anyone have the generic current vs. trip time formulas or curves, possibly from UL?

Thanks.
 
langjahr@comcast.net said:
For GFIs other than those that protect people, those that trip at higher currents, does anyone have the generic current vs. trip time formulas or curves, possibly from UL?

Thanks.
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If your asking about GFP (Ground Fault Protection for equipment) then the settings are usually determined by the engineer on a job by job basis.
 
GFP maximum trip settings are NEC mandated 1200 amps pickup, 1.0 second delay, specific trip curves are part of the system design per manufacture. I have actual trip curves for different manufactures if you care to view.
 
actual trip curves

actual trip curves

Yeah, thanks, I'd like to see them.

I'm not sure what exactly these devices are protecting, if it's not people.

Are they used to notify the user that leakage current in increasing, so equipment failure is imminent?
 
Basically the prime design is equipment protection which will also afford people protection.

If an arcing ground fault is limited to a maximum of 1200 amps for 1 second in lieu of 1200+ amps for an indeterminate amount of time, both equipment and people are afforded some protection.
 
Brain I am confused as in my limited experience the GFP setting are not determined by the manufacture but by the engineer of record for the particular job.

I'm not sure what exactly these devices are protecting, if it's not people.
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I was told that at the GFP is to protect the equipment from total self destruction. If you had a ground fault at the current levels that GFP is required it would keep burning / melting the equipment without tripping standard overcurrent protective devices.

Are they used to notify the user that leakage current in increasing, so equipment failure is imminent?
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I am sure that can be an option but I have never seen it, normally it just opens the circuit.

When we get the equipment from the factory for a new job all the settings are set for the most sensitive trip. If we do not get an engineers report telling us how to set the breakers / GFP we leave them that way.

This often results a simple 20 amp branch circuit ground fault dumping the main breaker for the building.

I once shorted out a 277 volt 20 amp lighting circuit only to have it open the 3000 amp feeder that eventually supplied that branch circuit.
 
How do you know that what you just installed is going to work. Just because you opened the box in which the mfg. shipped it to you, and you visually look and see the settings - That does not mean it will even operate, especially at those settings - it needs to be tested! Manufacturers make lots of mistakes - or should I say, those people building those items make mistakes.
 
do you have a specific application in mind?

do you have a specific application in mind?

No; I've been occasionally hearing about these things from this forum, and I'm curious as to why someone would need them and how they work, or are supposed to work.

If there are problems with these it helps to know what's inside even if only to the block-diagram level.
 
Johnson: I TEST EVERYTHING I INSTALL. All GFP,s are tested with a high current test set at all factory presets for current and time delay is tested at the delay setting per the coordination study if supplied. Otherwise the GFP is left set at minimum and tested for delay operation at the minimum setting.

Bob:

The equipment protection is foremost IMO because at 1200 amps 1.0 delay a sizable arc flash is still possible. Additionally you get across the bus and well you know the answer there. If GFP were advertised as people protection and someone died touching the bus, the lawyers would have a field day.
 
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brian john said:
Bob:

The equipment protection is foremost IMO because at 1200 amps 1.0 delay a sizable arc flash is still possible. Additionally you get across the bus and well you know the answer there. If GFP were advertised as people protection and someone died touching the bus, the lawyers would have a field day.
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Was that aimed at me? :confused:

I never said GFP was people protection, I said it was to prevent a melt down.
 
The jobs I have seen lately are specified by the engineer and tested by the manufacturer's techs.

If I am inspecting a service that requires GFP protection, I request a notification of the date of testing so I can be a witness.


My alterior motive is to ask the techs a lot of questions. Those guys are pretty talented in ways I never had an education. It has been good for me.
I have actually stayed and watched most of the different tests they perform on the equipment, it is very interesting.
 
Pierre C Belarge said:
The jobs I have seen lately are specified by the engineer and tested by the manufacturer's techs.
I have actually stayed and watched most of the different tests they perform on the equipment, it is very interesting.
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Pierre, there are many different protective relays to test. In my work we would contract that testing out to a company whose business is Electrical Testing. They would come in with their test equipment and go through all the different protective relays, taking as long as 3 days to perform all the testing. If you have the opportunity don't miss out on the chance to observe that.
The engineering company on these projects who did the design will have determined the required settings. The POCO will be generally have checked out the settings, and will even walk the system - often trips or permissives will tie in with their breakers. Initial energization they like to be there also.
The POCO would not be to happy if things were tripping off in their yard!
 
RHJohnson said:
Pierre, there are many different protective relays to test.
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That sounds like substation work?

I thought the discussion here was about NEC required GFP for services and feeders. :smile:
 
iwire said:
That sounds like substation work?

I thought the discussion here was about NEC required GFP for services and feeders. :smile:
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That is not sub station work...Some services are quite large..
 
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