sparky_007
Electrical
- Jan 16, 2019
- 7
Hello,
We have an existing 20MVA 13.8kV/6.9kV Wye-Delta transformer and the client wants to add another spare transformer (10MVA, 13.8kV/6.9kV Wye-Delta) that they have as back-up. Not possible to connect the 6.9kV secondary of the spare transformer to a spare breaker on the 6.9kV switchgear as it is a 1000ft run in an existing facility. Our manager suggested to add a 6.9kV 2000A manual transfer switch and connect to two transformer secondaries via cable bus directly without an Over Current Protection Device (OCPD).
Per the NEC 240.21(C)(4) and CEC 14-100(d) code, the transformer primary OCPD does not protect secondary side conductors and only exception allowed is when the cable directly terminates on an OCPD with other requirements as mechanical protection, etc. A fuse on each switch of the manual transfer switch would solve this problem but max rating available is 1200A.
Is my code understanding correct? Also, I wanted to know if anyone has faced this scenario before or any other solutions.
See attached sketch (without fuses)
We have an existing 20MVA 13.8kV/6.9kV Wye-Delta transformer and the client wants to add another spare transformer (10MVA, 13.8kV/6.9kV Wye-Delta) that they have as back-up. Not possible to connect the 6.9kV secondary of the spare transformer to a spare breaker on the 6.9kV switchgear as it is a 1000ft run in an existing facility. Our manager suggested to add a 6.9kV 2000A manual transfer switch and connect to two transformer secondaries via cable bus directly without an Over Current Protection Device (OCPD).
Per the NEC 240.21(C)(4) and CEC 14-100(d) code, the transformer primary OCPD does not protect secondary side conductors and only exception allowed is when the cable directly terminates on an OCPD with other requirements as mechanical protection, etc. A fuse on each switch of the manual transfer switch would solve this problem but max rating available is 1200A.
Is my code understanding correct? Also, I wanted to know if anyone has faced this scenario before or any other solutions.
See attached sketch (without fuses)