GFP too sensitive

[brother]

Just curious if anyone know of a diplomatic way to tell 'others' that it is not legal (code)/or wise to have a 800 amp gfp FEEDER for the panel trip BEFORE a 20 amp branch circuit breaker(with out ground fault) when you short the hot to ground on the 20 amp branch circuit (light fixture)??? Even though a gfp is more sensitive, the 20 amp branch still should trip before it does!!

 

[jim dungar]

Just curious if anyone know of a diplomatic way to tell 'others' that it is not legal (code)/or wise to have a 800 amp gfp FEEDER for the panel trip BEFORE a 20 amp branch circuit breaker(with out ground fault) when you short the hot to ground on the 20 amp branch circuit (light fixture)??? Even though a gfp is more sensitive, the 20 amp branch still should trip before it does!!

Unless an "emergency circuit" is involved, this is a design issue and is not a concern of the NEC.

Hospitals, required standby power, and critical power centers have specific coordination requirements.

 

[brian john]

Just curious if anyone know of a diplomatic way to tell 'others' that it is not legal (code)/or wise to have a 800 amp gfp FEEDER for the panel trip BEFORE a 20 amp branch circuit breaker(with out ground fault) when you short the hot to ground on the 20 amp branch circuit (light fixture)??? Even though a gfp is more sensitive, the 20 amp branch still should trip before it does!!

It is not illegal, bad design yes, poor coordination yes. Would I recommended resolving the issue yes. Where is the engineer on this? I would not recommend just willy nilly adjusting the GFP settings without some direction for CYA reasons.

Oh and why are you shorting loads on a 20 amp CB, or is this accidental faults.

 

[weressl]

Just curious if anyone know of a diplomatic way to tell 'others' that it is not legal (code)/or wise to have a 800 amp gfp FEEDER for the panel trip BEFORE a 20 amp branch circuit breaker(with out ground fault) when you short the hot to ground on the 20 amp branch circuit (light fixture)??? Even though a gfp is more sensitive, the 20 amp branch still should trip before it does!!

230.95 Ground-Fault Protection of Equipment.
.......​

(C) Performance Testing.​

​

​

The ground-fault protection
system shall be performance tested when first installed on
site. The test shall be conducted in accordance with instructions
that shall be provided with the equipment. A written
record of this test shall be made and shall be available to
the authority having jurisdiction.
.......................​

FPN No. 2: This added protective equipment at the service
equipment may make it necessary to review the overall
wiring system for proper selective overcurrent protection
coordination. Additional installations of ground-fault protective
equipment may be needed on feeders and branch
circuits where maximum continuity of electric service is
necessary.

____________________________________________________________
This maybe what you looking for. Although not specifically prohibits 'bad coordination' but requires selective operation that the equipment in your OP does not meet.​

 

[brother]

Oh and why are you shorting loads on a 20 amp CB, or is this accidental faults.

this is by accident of one of our workers. This is not intentional. Im not sure but i think 2005 NEC 110 might have some 'enforcement' here, because i was always told that the GFP feeders had to be tested every 3 or 4 years, or whenever there is MAIN new equipment installed, in accordance with the 'manufacturers instructions'.

 

[brother]

Unless an "emergency circuit" is involved, this is a design issue and is not a concern of the NEC.

Hospitals, required standby power, and critical power centers have specific coordination requirements.

We did have one situation where it WAS an EMERGENCY (Essential equipment) feeder/equipment that tripped.

 

[beanland]

Why GFP?

Why GFP?

GFP is not required on 208Y/120V service disconnects nor on service disconnects less than 1000A. Why would the 208Y/120V feeder OCPD have GFP? Sounds like an inappropriate application.

 

[jim dungar]

We did have one situation where it WAS an EMERGENCY (Essential equipment) feeder/equipment that tripped.

There was a period of time when GF was required on main services only. After awhile hospitals were required to have at least 2 levels of GF protection if they were going to have any. These two levels need to coordinate, but there is no requirement to coordinate any GF with any non-GF branch.

This is a concern that I have with 517 coordination requirements, since 2005 the NEC requires overcurrent coordination from "main to receptacle", but a GF on a branch circuit is allowed to trip off an entire feeder.

 

[brother]

There was a period of time when GF was required on main services only. After awhile hospitals were required to have at least 2 levels of GF protection if they were going to have any. These two levels need to coordinate, but there is no requirement to coordinate any GF with any non-GF branch.

This is a concern that I have with 517 coordination requirements, since 2005 the NEC requires overcurrent coordination from "main to receptacle", but a GF on a branch circuit is allowed to trip off an entire feeder.

I was always taught that GFP was NOT required on the alternate source for Emergency systems. This has been code for a long time. 2005 NEC 700.26

 

[brian john]

GFP is not required on 208Y/120V service disconnects nor on service disconnects less than 1000A. Why would the 208Y/120V feeder OCPD have GFP? Sounds like an inappropriate application.

BUT HOW DID YOU ASSUME it was 208/120? Did I miss something?

 

[jim dungar]

I was always taught that GFP was NOT required on the alternate source for Emergency systems. This has been code for a long time. 2005 NEC 700.26

You are correct, since GFP was first put into the code back in 70's, I am not aware of it ever being required on emergency systems.

I was addressing that "phase" coordination is required for all devices on both normal and emergency sources feeding legally required emergency systems, but GF coordination is only required between devices in hospitals supplied with a GF trip.

 

[brother]

You are correct, since GFP was first put into the code back in 70's, I am not aware of it ever being required on emergency systems.

I was addressing that "phase" coordination is required for all devices on both normal and emergency sources feeding legally required emergency systems, but GF coordination is only required between devices in hospitals supplied with a GF trip.

Yes, its only REQUIRED between the service and feeder gfp. However it is STRICTLY forbidden (and for good reason) to have GFP between the onsite generating unit(s) and the essential electrical system transfer switch or on the load side of the transfer switch, NEC 2005 517.17 (B)(1-3)

But in Gods name i cannot comprehend why ANYONE would want/allow a gfp feeder breaker, required or not, normal power or emergency, to trip before the branch circuit breakers as small as 20 amps when someone or some bad equipment shorts to ground.

 

[brian john]

But in Gods name i cannot comprehend why ANYONE would want/allow a gfp feeder breaker, required or not, normal power or emergency, to trip before the branch circuit breakers as small as 20 amps when someone or some bad equipment shorts to ground.

1. Because the average construction electrician has no idea what to do with GFP.
2. Because the average electrical EC avoids testing and proper setup during construction.
3. Because the average electrical engineer avoids the issue at all cost.

So it is left to the end user to do something they usually do one of three things.

Pull the control fuses, shut it down.
Randomly pick a setting, based on lets try this.
Hire a firm to resolve the issue.

 

[cadpoint]

In the OP and negating GFP for a minute he said it was a light fixture.

Could it have been the load side of the ballast that crossed, high voltage low amps? I've seen this happen before on new gear, not just that, did the bonded item get touched as well ? The big gear tripped.

In our same situation all three where brought together.

We had the basic safety shut-down, what happened, were where you, What, When, Where, Why ? & for our saftey...

Does anything make sense when electricty trying to go to infinity ?

No, It wasn't me, honest...

Great reading, thanks ...

 

[brother]

1. Because the average construction electrician has no idea what to do with GFP..

There really needs to be some serious education on this issue then along mwbcs and etc..

2. Because the average electrical EC avoids testing and proper setup during construction...

this is where the inspectors need to enforce and FINE people for this. This also will help the industry, hopefully stop dumbin it down with NEC excessive codes

3. Because the average electrical engineer avoids the issue at all cost...

I really dont know all the costs involved.

So it is left to the end user to do something they usually do one of three things.

Pull the control fuses, shut it down.
Randomly pick a setting, based on lets try this.
Hire a firm to resolve the issue.

Maybe its best just to hire the firm, the other 2 just seems too 'hacky' and 'diy'.

 

[iwire]

There really needs to be some serious education on this issue then along mwbcs and etc..

I disagree, it is beyond the scope of being a typical electrician to know how to properly set a breaker.

I have done it many times but only following the settings provided by the jobs EE.

The equipment arrives with the settings low and quick I would be a fool to touch those settings without guidance from the EE, it is just not my job to guess.

Maybe its best just to hire the firm, the other 2 just seems too 'hacky' and 'diy'.

There is no choice but to have a coordination study done, that is the only way to determine the proper settings.

In the big picture having the setting low and quick is much safer then having them set to high or to slow.

After a few trips someone will come up with the $ to have coordination study done.

 

[brian john]

Originally Posted by brian john
3. Because the average electrical engineer avoids the issue at all cost...

I really don't know all the costs involved.

THEIR COST:
Not having sold a coordination study as part of the design package.
Personal time and involvement.

There is no choice but to have a coordination study done, that is the only way to determine the proper settings.

In the big picture having the setting low and quick is much safer then having them set to high or to slow.

After a few trips someone will come up with the $ to have coordination study done.

In my experience less than 25% of the time.

1 and 2 are usual options picked.

My thoughts

Set low with no time delay - tripping from 20 amp CB and higher.

Set high. Minimize's so called "nusinace tripping" but extends the possible damage from an arcing ground fault over a lower setting. BUT STILL NEC LEGAL 230.95 (A).

IMO and strictly my opinion, with a 400 amp and .1 sec delay this setting will get you out of the range of 20 and 30 amp OCPs minimizng nusinace tripping.
It is not possible to fully avoid tripping from downstream devices.

I'd like to see the delay as fast as possible.

 

[weressl]

GFP is not required on 208Y/120V service disconnects nor on service disconnects less than 1000A. Why would the 208Y/120V feeder OCPD have GFP? Sounds like an inappropriate application.

The majority of faults start out as ground fault, then escalate into phase-to-phase faults. So protecting your switchboard against ground fault minimizes damage. Not required by Code but good engineering practice.

 

[brian john]

Example:

Went to a job today GFP has been tripping when fire alarm system is in alarm. Electrician before me jacks up the GFP Amperage setting and time delay. Bells ring and it trips they suggest calling me.

Seem simpler than an adjustment issue. Need to give a T&M NTE to investigate and test off hours.

 

[beanland]

GFP Option

GFP Option

The majority of faults start out as ground fault, then escalate into phase-to-phase faults. So protecting your switchboard against ground fault minimizes damage. Not required by Code but good engineering practice.

I agree that GFP is a good idea BUT if it cannot be properly coordinated with other devices, it is a poor option. In POCO high-voltage work, we often use a ground trip that is 50% of the phase trip. This allows unbalance and provides coordination margin for downstream devices. However, only where there is ONLY phase-phase connected load or delta transformers can you safely set the GFP to low values, e.g. below 10% of the phase trip. Otherwise, you will never get coordination.

To get really good switchboard protection, you need differential relaying. That is standard POCO practice.