leroy.martin
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- Ephrata, Pa., Usa
I need clarification on Article 705.12(D)(3)
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Ground Fault
- Thread starter leroy.martin
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BillK-AZ
Senior Member
- Location
- Mesa Arizona
This can be a difficult requirement.
Unfortunately, on larger systems, a significant part of any ground fault current may be sourced by the PV inverter, reducing the ground fault current through the main device below the trip point for the GFP main breaker.
One common situation is connecting a utility-interactive inverter to an electrical system that requires ground-fault protection (see Art 210.12) such as 3-phase 480-volt services of 1000A or higher. This requires that both the main overcurrent/ground-fault device and the utility-interactive inverter overcurrent/ground-fault device (usually a CB) have ground-fault protection and that the ground fault detection levels be coordinated.
Sounds simple, but this is difficult in practice because most overcurrent/ground-fault devices are marked Line and Load and are not suitable for back-feeding. This is because breakers are listed to UL 489 and UL 489 makes no reference to NEC Art 690.64(B)(3), but it does make reference to Art 210.12 that requires the GFP feature. As a result, the test sequence for UL 489 does not test breakers that have the ground-fault option for proper operation when back fed. Back in 2008 I discussed this with an UL test engineer involved with these tests and he stated that UL had never tested any CBs with ground fault protection options for operation when back fed as that would be an extra cost. Some manufacturers have done their own in-house testing and will issue letters that specific breakers are suitable for back-feeding and ground fault protection, but it is not 'Listing' and the AHJ will need convincing. The problem is legal risk, not actual operation as desired.
There is a real problem in that some older ground-fault protection devices use a coil to trip the breaker or switch in the event that a ground fault is detected, and rely on the opening of the breaker or switch to remove power from the coil quickly before the coil is damaged. If there is an utility-interactive inverter on the load side of the breaker or switch and it continues to operate for the maximum time allowed by UL-1741, the coil can be damaged.
There is also a problem in that many panelboards use fused switches that are operated by separate ground-fault protection (GFP) devices made by other manufacturers and the combination has not been tested for suitability for back feeding, but each of the parts taken separately will operate with current flow in either direction. Siemens has made panelboards with a Siemens fused switch and a Pringle GFP controller (Pringle is a division of Eaton).
The above is likely to be more confusion than clarification for many. Dealing with this on large systems can be difficult and expensive.
Line side connections avoid this problem.
Unfortunately, on larger systems, a significant part of any ground fault current may be sourced by the PV inverter, reducing the ground fault current through the main device below the trip point for the GFP main breaker.
One common situation is connecting a utility-interactive inverter to an electrical system that requires ground-fault protection (see Art 210.12) such as 3-phase 480-volt services of 1000A or higher. This requires that both the main overcurrent/ground-fault device and the utility-interactive inverter overcurrent/ground-fault device (usually a CB) have ground-fault protection and that the ground fault detection levels be coordinated.
Sounds simple, but this is difficult in practice because most overcurrent/ground-fault devices are marked Line and Load and are not suitable for back-feeding. This is because breakers are listed to UL 489 and UL 489 makes no reference to NEC Art 690.64(B)(3), but it does make reference to Art 210.12 that requires the GFP feature. As a result, the test sequence for UL 489 does not test breakers that have the ground-fault option for proper operation when back fed. Back in 2008 I discussed this with an UL test engineer involved with these tests and he stated that UL had never tested any CBs with ground fault protection options for operation when back fed as that would be an extra cost. Some manufacturers have done their own in-house testing and will issue letters that specific breakers are suitable for back-feeding and ground fault protection, but it is not 'Listing' and the AHJ will need convincing. The problem is legal risk, not actual operation as desired.
There is a real problem in that some older ground-fault protection devices use a coil to trip the breaker or switch in the event that a ground fault is detected, and rely on the opening of the breaker or switch to remove power from the coil quickly before the coil is damaged. If there is an utility-interactive inverter on the load side of the breaker or switch and it continues to operate for the maximum time allowed by UL-1741, the coil can be damaged.
There is also a problem in that many panelboards use fused switches that are operated by separate ground-fault protection (GFP) devices made by other manufacturers and the combination has not been tested for suitability for back feeding, but each of the parts taken separately will operate with current flow in either direction. Siemens has made panelboards with a Siemens fused switch and a Pringle GFP controller (Pringle is a division of Eaton).
The above is likely to be more confusion than clarification for many. Dealing with this on large systems can be difficult and expensive.
Line side connections avoid this problem.
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