GFI setting calculation

Status
Not open for further replies.
Cloud

Cloud

Member
Location
PH/VN
Hi guys. I just want confirmation on this. As taught, the setting for the GFI is 20% the max amp of the panel. We have 250A 380V panel.
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
I think the NEC only requires GFPE on equipment 1000 amps or greater.

The requirements are in 230.95.

230.95 Ground-Fault Protection of Equipment. Groundfault
protection of equipment shall be provided for solidly
grounded wye electric services of more than 150 volts to
ground but not exceeding 600 volts phase-to-phase for each
service disconnect rated 1000 amperes or more.
 
T

T.M.Haja Sahib

Guest
jumper said:
I think the NEC only requires GFPE on equipment 1000 amps or greater.

The requirements are in 230.95.

230.95 Ground-Fault Protection of Equipment. Groundfault
protection of equipment shall be provided for solidly
grounded wye electric services of more than 150 volts to
ground but not exceeding 600 volts phase-to-phase for each
service disconnect rated 1000 amperes or more.
Click to expand...
I think the intent of the code is to afford protection against arcing faults and blasts and so the OP is not prohibited to provide a GFPE?
 
D

dana1028

Senior Member
Location
San Francisco Bay area
Cloud said:
As taught, the setting for the GFI is 20% the max amp of the panel. We have 250A 380V panel.
Click to expand...

Ignoring the code not requiring the GFPE in 230.95 - what about the OPs querry about the 20% setting? I am not familiar with this...do any of our engineer's have some feedback about this 20% setting? Thank you in advance
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
dana1028 said:
...do any of our engineer's have some feedback about this 20% setting...
Click to expand...
Its called 'pick and click'. It basically ignores the fact that the GF relay is part of a system of protective devices.

In almost every GF coordination I have performed, the time delay setting has been more critical than the current pick up point.
 
brian john

brian john

Senior Member
Location
Leesburg, VA
You have a 250 amp Main Circuit breaker at 480 VAC, with Ground Fault Protection?

Ideally the design engineer should provide the setting of the GFP relay as part of the coordination study, unfortunatly in my expierence 99% of them skip that little bit of work.

Is there GFPE upstream of the 250 Amp CB?

Is the GFPE part of the circuit breaker?

What are the available setings, current and time delay?

What is the maximum size CB in the panel to be protected, excluding the main CB?

If you did 20% or 50 amps, everytime you had a ground fault on a branch circuit the main would trip.
 
brian john

brian john

Senior Member
Location
Leesburg, VA
dana1028 said:
Ignoring the code not requiring the GFPE in 230.95 - what about the OPs querry about the 20% setting? I am not familiar with this...do any of our engineer's have some feedback about this 20% setting? Thank you in advance
Click to expand...

I was taught years ago as a rule of thumb as they say.

This is for main service protection.

20%-30% of the main OCP and time delay at .1 seconds, with the minimum setting at 400 amps as this would allow the majority of the CBs in a building (20 and 30 amp branch circuits) to clear the fault avoidining nusiance tripping

4000 amp main 800-1200 amps
3000 amp main 600-900 amps
2000 amp main 400-800 amps
1200 amp main 400 amps
1000 amp main 400 amps

How this compares to an actual coordination study if one was ever done I do not have any reference.

One job we were involved with the engineer had in the coordination study for a 4000 amp main, the GFPE relay to be set at 200 amps .1 time delay, after countless nusiance trips, he said jack it to 800 amps .5 seconds. I have no clue if he ever did a re-evaluation or was just sick of hearing from the client.
 
Cloud

Cloud

Member
Location
PH/VN
brian john said:
You have a 250 amp Main Circuit breaker at 480 VAC, with Ground Fault Protection?

Ideally the design engineer should provide the setting of the GFP relay as part of the coordination study, unfortunatly in my expierence 99% of them skip that little bit of work.

Is there GFPE upstream of the 250 Amp CB?

Is the GFPE part of the circuit breaker?

What are the available setings, current and time delay?

What is the maximum size CB in the panel to be protected, excluding the main CB?

If you did 20% or 50 amps, everytime you had a ground fault on a branch circuit the main would trip.
Click to expand...

There is no GFI on the upstream of this DB.
The GFI trip unit is stand alone.
I don't have the time delay setting, but it is set to 10 amps.
This is a distribution panel, maximum breaker supported is about 50 amps.

I am just wondering if the settings by the operations are correct- or rather enough to avoid nuisance tripping. The panel is being use by production, we cannot afford any tripping.

Thanks!
 
Cloud

Cloud

Member
Location
PH/VN
zog said:
Then hire an engineer to perform a coordination study. If it is so important perhaps trusting a bunch of yahoos in the web is not the best idea.
Click to expand...

Well, they have had before. All the values are set and tools are already running. I am just curious on how did they compute, and if it is correct- or the 20% thing that I know is correct. Thanks!
 
Status
Not open for further replies.
Top