OCP of outdoor potential transformers
OCP of outdoor potential transformers
(OP)
According to NESC C-2 instrument transformers are not required over current protection. The NEC indicates all transformers need OCP. For medium voltage systems, in switchyards and on poles, is fusing of metering potential transformers optional?






RE: OCP of outdoor potential transformers
Current (CT) and Voltage (VT or PT)
CT do not require an OCP....VT/PT does...
At least I have not seen a VT/PT withoout a fuse on MV systems.
RE: OCP of outdoor potential transformers
RE: OCP of outdoor potential transformers
I've never seen a PT that wasn't fused, though. And I have no idea if the unfused PT's you're dealing with are legal or not.
One more thought on this -- if a PT was manufacturer installed, they would not be held to NEC. But if it was field installed, then NEC would apply. There might be some different requirements if you're not building to NEC. . . .
RE: OCP of outdoor potential transformers
In many cases for revenue-metering applications, metering components are under exclusive control of utilities, so are not bound by the NEC.
NEC 450-3(C) implies that outdoor VTs may be permitted without primary overcurrent protection. NEC 408.32 requires overcurrent protection for instruments served by VTs
Secondary fusing offers limited protection to VTs. ANSI C57.13-1993 §7.7 requires that one-second secondary-side short circuits will not damage VTs.
Some discussion in General Electric GEP-9186-6 — Section 5 Applications Information Primary Fuses For Voltage Transformers
RE: OCP of outdoor potential transformers