P.Oates
New User
- Location
- Siskiyou County Building and Safety
This is an email we received from net metering engineer for Pacific Power. We have an approved installed 180 Kw Gnd. Mtd. PV System. Pacific Power signed off and the system and approved the sites for interconnection, the system is built, inspected, and are currently in operation.
The Pacific Power Engineer did a secondary review of the installation design during a troubleshooting call . . . and he has identified an issue with the design that doesn’t conform to the NEC. He is concerned about having proper protection in place for the customer’s equipment and PP. However, the PP engineer don’t claim to be an NEC expert (the power utility stays out of that arena) and brought it up with the engineering firm that did the design. After a lot of back and forth between PP engineer and engineer of record . . . well, they haven’t reached an agreement.
Can you help us Siskiyou County out in interpreting the code correctly?
Pacific Power required an effective grounding system be included in the installation to prevent the generation system from driving an overvoltage condition during a line-to-ground fault (the circuit feeding this customer already had a sizable amount of private generation before the customer built their systems).
The item in question is hex-marker 6: a fused disconnect switch in front of the generation system and the effective grounding transformer. The PP engineer believes (and here’s where I need your help) that the fuse is too large to protect the effective grounding transformer, per NEC 450.3 (B). When the PP engineer brought this up with the engineering firm, they argued that NEC 450 doesn’t apply here due to the effective grounding transformer being a current transformer (?) and then later referred me to 450.5 for grounding auto-transformers. I can’t see how a wye-delta voltage transformer could be argued this way . . . but I may not have the right interpretation of the NEC.
Can you help settle the debate on whether NEC 450 applies here?
If any further info or clarification is needed, please let me know. I’m happy to provide whatever I can.
Philip
The Pacific Power Engineer did a secondary review of the installation design during a troubleshooting call . . . and he has identified an issue with the design that doesn’t conform to the NEC. He is concerned about having proper protection in place for the customer’s equipment and PP. However, the PP engineer don’t claim to be an NEC expert (the power utility stays out of that arena) and brought it up with the engineering firm that did the design. After a lot of back and forth between PP engineer and engineer of record . . . well, they haven’t reached an agreement.
Can you help us Siskiyou County out in interpreting the code correctly?
Pacific Power required an effective grounding system be included in the installation to prevent the generation system from driving an overvoltage condition during a line-to-ground fault (the circuit feeding this customer already had a sizable amount of private generation before the customer built their systems).
The item in question is hex-marker 6: a fused disconnect switch in front of the generation system and the effective grounding transformer. The PP engineer believes (and here’s where I need your help) that the fuse is too large to protect the effective grounding transformer, per NEC 450.3 (B). When the PP engineer brought this up with the engineering firm, they argued that NEC 450 doesn’t apply here due to the effective grounding transformer being a current transformer (?) and then later referred me to 450.5 for grounding auto-transformers. I can’t see how a wye-delta voltage transformer could be argued this way . . . but I may not have the right interpretation of the NEC.
Can you help settle the debate on whether NEC 450 applies here?
If any further info or clarification is needed, please let me know. I’m happy to provide whatever I can.
Philip
