250.121 Exception

m sleem

Senior Member
Location
Cairo
If i have an AHU connected supplied by 5 wires, can the EGC being terminated to water pipes per the exception of NEC 250.121?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
I don't think so. Are you dealing with an equipment grounding conductor or grounding electrode conductor? 250.121 is about the equipment grounding conductor being used as a grounding electrode conductor.
 

m sleem

Senior Member
Location
Cairo
I understand that the egc connected to AHU along with life conductors, the bonding between AHU's egc and water pipe is called gec. Correct?
 

m sleem

Senior Member
Location
Cairo
I don't think so. Are you dealing with an equipment grounding conductor or grounding electrode conductor? 250.121 is about the equipment grounding conductor being used as a grounding electrode conductor.
I mean the EGC of the AHU if bonded to chilled water pipes and acts as GEC, i know the EGC of water pipes shall be extended from the electrical source e.g. MCC panel, but i am trying to understand the exception and use it.

Note:
IMHO, This forum is not the same as it was before, all members were cooperative and quick to respond unlike what we are now :(
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
I think the issue is trying to understand what the ahu has to do with the grounding electrode conductor. Doesn't the electrical system already have a gec at the service.
 

m sleem

Senior Member
Location
Cairo
Hi Dennis,

I thought GEC could be any location as long as it bonds different electrodes not only at service.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Hi Dennis,

I thought GEC could be any location as long as it bonds different electrodes not only at service.
GEC per NEC definition is "a conductor used to connect the system grounded conductor" (neutral) "or the equipment" (if supplemental grounding) "to a grounding electrode or to a point on the grounding electrode system."
How do you call the supplemental bonding wire from AHU body to nearest grounding bar?
Per NEC definition of EGC: "the conductive path(s) that provides a ground-fault current path and connects normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both."

NEC definition: "Bonding Conductor or Jumper. A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected."
I mean the EGC of the AHU if bonded to chilled water pipes and acts as GEC, i know the EGC of water pipes shall be extended from the electrical source e.g. MCC panel, but i am trying to understand the exception and use it.
I dont think your chiller pipe would fit definition of GEC, metal water pipes must be bonded to to the GE (Gounding Electrode) eventually, but it's not acting as an EGC or a GEC, it simply is an attempt to limit objectionable current from presenting on the metal part. Metal conduit can serve as an EGC if installed in a manner to allow continuous bond, but not the GEC. The metal water pipes can be used as the GE under specific criteria none of which you have mentioned. Thus your attempt to use the exception in 250.121 for this seems to be not applicable.
Trying to understand your reason to want to use the exception?
 
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