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The common 30, 45, 75, 112.5, and 150 KVA 480/208/120 Volt, Delta to Y
Dry-type transformers are being found without grounding electrode conductors and
without a grounding electrode as required by the NEC section 250-26. These
transformers of the solidly-grounded type are "separately derived AC
systems," and the grounding requirements are almost like a service. The
grounded conductor terminal, commonly referred to as XO, on the secondary side
must be grounded to the nearest available effectively grounded structural member
(building steel), water pipe, or other electrodes as specified in NEC section
250-81 and 250-83 where the effectively grounded structural member (building
steel) or water pipe are not available. "The grounding electrode shall be
as near as practical to and preferably in the same area as the grounding
conductor connection to the system." This system is not the service system
but the separately derived A.C. system.
Also, a bonding jumper sized in accordance to 250-79(d) for the derived
phase conductors must bond the grounded conductor to the equipment grounding
conductors.
Engineers and installers repeatedly attempt to use the equipment grounding
conductor brought in with the primary power as a grounding electrode conductor.
This is a clear violation of NEC section 250-26.
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