GEC for Tranformer in High Rise Building

[infinity]

Can someone explain why you would need to run a GEC from a transformer to building steel or a common grounding electrode on the 20th floor of a high rise building? What actual purpose would this serve? IMO it don't really do much.

 

[augie47]

This Article helps a little:
http://www.ecmag.com/section/codes-standards/ground-or-not-ground-question

I can see where you would want to establish a zero reference between systems so would not have potential between other systems (communication, piping, etc)

 

[electrofelon]

Can someone explain why you would need to run a GEC from a transformer to building steel or a common grounding electrode on the 20th floor of a high rise building? What actual purpose would this serve? IMO it don't really do much.

I assume you are not questioning the reasons or value of system grounding, but rather, why isn't the egc run with the supply sufficient for system grounding of the SDS? If so, I do not know the answer. I would conjecture that, like many people, the NEC puts disproportionate importance on grounding/earthing and the integrity of the GEC.

 

[ActionDave]

I agree with electrofelon, there is so much irrationality surrounding GEC/earthing you are lucky to find somebody that can talk about them in something other than reverent, hushed tones.

 

[infinity]

I assume you are not questioning the reasons or value of system grounding, but rather, why isn't the egc run with the supply sufficient for system grounding of the SDS? If so, I do not know the answer. I would conjecture that, like many people, the NEC puts disproportionate importance on grounding/earthing and the integrity of the GEC.

Yup that's it. The transformer has an EGC run with the primary conductors that's already connected to the system GES at the service. At the transformer that same EGC is connected to the X0 through the system bonding jumper. Seems like the GEC is serving little or no purpose.

 

[mbrooke]

Yup that's it. The transformer has an EGC run with the primary conductors that's already connected to the system GES at the service. At the transformer that same EGC is connected to the X0 through the system bonding jumper. Seems like the GEC is serving little or no purpose.

I fully agree. The most logical conclusion that I can think of being that the NEC really doesn't want the EGC getting lost, so the GEC is simply a backup for fault current. Much like medical areas in the code.


But in all honesty it might come from the grounding myth days. (Think of when pools had to be bounded around a single ground rod) If the earth truthfully was a great electron sponge, that GEC would be an expressway... assuming your building is not steal. In reality regardless of what soil is capable of, building steal has an ohm reading well below any practical GEC going up 20 stories.

 

[big john]

Even just changing the wording would do a lot to convince me that this isn't arcane voodoo. But when all this emphasis is still put on "grounding" while the reality is the earth plays a very minor role in most LV electrical systems, it makes me think the guys writing the standards are just sticking with their outdated boilerplate because they're afraid of change.

 

[mbrooke]

Even just changing the wording would do a lot to convince me that this isn't arcane voodoo. But when all this emphasis is still put on "grounding" while the reality is the earth plays a very minor role in most LV electrical systems, it makes me think the guys writing the standards are just sticking with their outdated boilerplate because they're afraid of change.

You want my honest opinion contrary to the popular? I think they simply don't understand it in full. Its the only conclusion I can reach. They don't know the outcome- and in turn the perceived liability- which would require their understanding of theory to be articulated.

 

[infinity]

This Article helps a little:
http://www.ecmag.com/section/codes-standards/ground-or-not-ground-question

I can see where you would want to establish a zero reference between systems so would not have potential between other systems (communication, piping, etc)

I get the zero reference idea but in many cases the system EGC(s) that are part of the transformer supply are larger than the maximum required GEC of #3/0. In that case I don't see much of a point in using any GEC.

 

[Smart $]

Yup that's it. The transformer has an EGC run with the primary conductors that's already connected to the system GES at the service. At the transformer that same EGC is connected to the X0 through the system bonding jumper. Seems like the GEC is serving little or no purpose.

You are aware you can run a combo EGC/GEC, right?

FWIW, it will typically be larger than the required EGC... and if you have building steel in the immediate area, it may be a lot less expensive to just run the separate GEC to that building steel than running the combo EGC/GEC.

 

[electrofelon]

Even just changing the wording would do a lot to convince me that this isn't arcane voodoo. But when all this emphasis is still put on "grounding" while the reality is the earth plays a very minor role in most LV electrical systems, it makes me think the guys writing the standards are just sticking with their outdated boilerplate because they're afraid of change.

I agree. Not only are the strict requirements for the gec not commensurate with the importance of their purpose, but also, and perhaps worse, it helps perpetuate grounding myths.