IEEE Std 141-1993 11.8.1 Current Transformers 4th paragraph states:
"Current transformers must have a secondary circuit ground at one point when they are required to be grounded. The National Electrical Code (NEC), ANSI/NFPA 70-1993 [B5], Section 250-L, specifes minimum grounding requirements for instrument transformers. The ground will establish a firm ground reference point and will restrict the buildup of static voltages caused by the high-voltage conductor(s)."
I am unable to locate Section 250-L in the 2005 NEC, the only copy I have access to.
Can someone summarize what the section intends? Is it common to ground the neutral conductors of a 3-phase CT arrangement for safety reasons? What situations would make it legitimate to leave it ungrounded.
Our particular arrangement was feeding information into a genset control panel and the manufacturer's info suggested grounding was optional. Unfortunately as I write this I no longer have a copy of the manual in front of me (it is at site) and cannot recall if there were criteria attached the the "optional" statement.
This is for a Canadian installation and I cannot locate any specific reference in the Canadian code for such installations. It appears it was also removed from the NEC but I am wondering what was there and why, and why it was removed.
Regards,
Mark Dumont
Calgary, Alberta
"Current transformers must have a secondary circuit ground at one point when they are required to be grounded. The National Electrical Code (NEC), ANSI/NFPA 70-1993 [B5], Section 250-L, specifes minimum grounding requirements for instrument transformers. The ground will establish a firm ground reference point and will restrict the buildup of static voltages caused by the high-voltage conductor(s)."
I am unable to locate Section 250-L in the 2005 NEC, the only copy I have access to.
Can someone summarize what the section intends? Is it common to ground the neutral conductors of a 3-phase CT arrangement for safety reasons? What situations would make it legitimate to leave it ungrounded.
Our particular arrangement was feeding information into a genset control panel and the manufacturer's info suggested grounding was optional. Unfortunately as I write this I no longer have a copy of the manual in front of me (it is at site) and cannot recall if there were criteria attached the the "optional" statement.
This is for a Canadian installation and I cannot locate any specific reference in the Canadian code for such installations. It appears it was also removed from the NEC but I am wondering what was there and why, and why it was removed.
Regards,
Mark Dumont
Calgary, Alberta
