mcelweec@gmail.com
CMAC1
- Location
- NYC
- Occupation
- Electrician
On a service over 1000a at 480v are there any parameters on the control circuit feeding the GFP relay?.I cant find anything in the NEC.
gfp relay
- Thread starter mcelweec@gmail.com
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rcwilson
Senior Member
- Location
- Redmond, WA
GFP Power Supply
GFP Power Supply
It's been a few years since I tested a GF system. I believe there is a UL requirement:
Control circuit should be from 480 phase-phase, not 277V phase-ground and not from some downstream panelboard. The Control Power Transformer (CPT) and associated fuses have to be sized to supply tripping current during a ground fault when the faulted phase is at 0 volts to ground. During the ground fault the 120V control voltage could drop to 67 V or less since the 480 V input is down to 277V.
Usually, the ground fault power supply is tapped off the line side of the breaker or switch. Otherwise there is no protection when the device is first closed.
When testing GFP's we would simulate fault current and verify trip timing. The last test was putting 277V on the CPT and simulating a fault. Several times the low voltage caused the devices to pull enough current to blow the control fuse. (I think the low voltage slowed down the trip solenoid, making its current last too long for the fuse.)
GFP Power Supply
It's been a few years since I tested a GF system. I believe there is a UL requirement:
Control circuit should be from 480 phase-phase, not 277V phase-ground and not from some downstream panelboard. The Control Power Transformer (CPT) and associated fuses have to be sized to supply tripping current during a ground fault when the faulted phase is at 0 volts to ground. During the ground fault the 120V control voltage could drop to 67 V or less since the 480 V input is down to 277V.
Usually, the ground fault power supply is tapped off the line side of the breaker or switch. Otherwise there is no protection when the device is first closed.
When testing GFP's we would simulate fault current and verify trip timing. The last test was putting 277V on the CPT and simulating a fault. Several times the low voltage caused the devices to pull enough current to blow the control fuse. (I think the low voltage slowed down the trip solenoid, making its current last too long for the fuse.)
mcelweec@gmail.com
CMAC1
- Location
- NYC
- Occupation
- Electrician
I agree 100%,the engineer missed the GFP,the manufacturer has given up on correcting his mistakes and i am stuck in the middle.The trip unit "approved" is 120v,this is why my mind is wandering.
brian john
Senior Member
- Location
- Leesburg, VA
Most GFPs are 120 VAC some older Brown Boveri were 240 VAC, then there are some DC trips, these are 120 VDC.
mcelweec@gmail.com
CMAC1
- Location
- NYC
- Occupation
- Electrician
Where does the control voltage originate from?
brian john
Senior Member
- Location
- Leesburg, VA
Depends on the manufacture and the type of distribution system.
Typically a line bus tap to control fuses and then a 480 VAC to 120 VAC transformer.
This feeds the GFP relay, Blown fuse device, phase failure relay , for trip operation if these are installed.
Typically a line bus tap to control fuses and then a 480 VAC to 120 VAC transformer.
This feeds the GFP relay, Blown fuse device, phase failure relay , for trip operation if these are installed.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I often include a 'capacitor trip' device rather than just a control power transformer. These are especially helpful when Phase Loss has been added to the protection circuit.
ATSman
ATSman
- Location
- San Francisco Bay Area
- Occupation
- Electrical Engineer/ Electrical Testing & Controls
I have never seen a capacitor trip device used (nor required) on LV systems.
Usually they are seen on 4160V systems and above. Can someone explain why? Code? :-?
Please do not go into a lengthy discussion on how they work.
Tony
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
People don't understand what they are specifying/installing.
After all if the CODE does not require it why pay for it.
I hardly ever put capacitor trip on my MV equipment, I usually put in a battery bank. I almost always use a cap trip with phase loss. I can't remember putting a cap trip on a GF only system.
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