mini-load center bonding

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don_resqcapt19 said:
However it is not completely clear. I read it as permitting the SDS to be remote from the service equipment and running the GEC to the service equipment. I think that may not be what the intent is. I think the intent may be that the SDS is physically installed in the service equipment.
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Yeah, that could be the difference between power for the SDS originating in the service and the actual origin of the SDS conductors (i.e. the secondary terminals) being in the service. You can argue either way. Maybe there are some CMP comments in the archives to clarify their intention?
 
Equipment grounding conductor can not be used as a grounding electrode conductor. I can understand that.

How about using a grounding electrode conductor for equipment grounding?

At grain storage bin locations I often find myself with 480/277 service panel supplying mostly motor loads and maybe some 277 volt lighting. We often have a 5 to 10 KVA 120/240 transformer for some general purpose receptacles. The service panel, or even a feeder supplied panel in some cases, along with the transformer and its supplied loadcenter are all mounted on same free standing structure, which may be metal but in no way ever has enough buried/concrete encased metal to qualify as a grounding electrode.

So if I have a 5 KVA transformer, do I have to run the minimum 250.122 EGC of 14 AWG for the transformer primary plus a 250.66 8 AWG minimum GEC (the only electrode to tie it to is the ground rod(s) at the 480/277 panel) or is a single 8 AWG acceptable to do both the EGC and GEC job for the SDS? Seems stupid to me to run both, and I never have in the past, and never have been called on any violations either, that don't mean the inspector necessarily knows exactly what is NEC compliant here though. We are usually talking about total conductor length of maybe 6 feet max.
 
don_resqcapt19 said:
Prior to the 2011 code, I could see no reason why you could not unsize the primary EGC and use it both as the primary EGC and the GEC for the secondary of the transformer. Yes, you would have to comply with the rules for both conductors, but it was doable...now comes the 2011 code and they specifically tell us that you cannot use the EGC as a GEC.
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This is what we always did, we sized (unsized?) the GEC per table 250.66 and used it as also the EGC, when 250.121 showed up, I took it to confirm that you must size the conductor per table 250.66 and not table 250.122, so it made sense that you couldn't use a EGC because in many cases it would be undersized, but as long as the conductor was sized for the GEC it would still be allowed to run one conductor to serve both, but I think someone posted something that said it was still not allowed, which makes no sense if it is sized from table 250.66? 250.121 says you can't use a EGC for a GEC which makes sense because the conductor will be to small, but why can't it be the other way around? to me the code doesn't say you can't use a GEC for a EGC and is done in other parts of the code such as an alternative method to ground ungrounded receptacles?
 
kwired said:
Equipment grounding conductor can not be used as a grounding electrode conductor. I can understand that.

How about using a grounding electrode conductor for equipment grounding?
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I think this is semantics. If the grounding electrode conductor is used for the equipment grounding conductor then the equipment grounding conductor is being used as the grounding electrode conductor.
 
The code making panels point in not using a single conductor for both purposes is that under normal operating conditions an EGC should not have current flow, but a GEC can have current flow under normal operating conditions.
 
Thanks

Thanks

Thank you to all who responed to this quest.. And thanks for the code references.I will make certain we bond/cadweld the transformer secondary to the building steel.And yes they would like to tar and feather me.
 
don_resqcapt19 said:
The code making panels point in not using a single conductor for both purposes is that under normal operating conditions an EGC should not have current flow, but a GEC can have current flow under normal operating conditions.
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Understandable for a GEC at a service, where is the current going to come from/go to under normal operating conditions for a separately derived system that is installed properly?
 
don_resqcapt19 said:
The code making panels point in not using a single conductor for both purposes is that under normal operating conditions an EGC should not have current flow, but a GEC can have current flow under normal operating conditions.
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I must ask, why would a GEC have current flowing on it between the transformer and the service feeding the transformer? if it does so will the EGC as when run like this they will be in parallel with each other.

To me that reason makes no sense at all?

It also make no electrical sense to require another conductor to be run in the same raceway between the service equipment and a transformer the service equipment feeds, when one sized for the larger requirement of 250.66 would do the same thing and like I said they would be paralleled anyways.

The second problem in requiring a grounding electrode system for a SDS is if you don't have building steel or a water pipe available exception 1 to 250.30(A)(4) allows installing a 250.52(A) electrode which does not relinquish the requirement to bond this new electrode to existing electrode system of the same building as pointed out by the FPN #2 to 250.4(A)(4) so you can't even drill a rod in a call it a day as you would still have to run an electrode bonding jumper back to the buildings electrode system, so even installing a made electrode does nothing to help.

Last if you have run a metallic raceway to supply the transformer then you have to make it electrically continuous because it contains the electrode conductor as required in 250.64(E)

I have never understood why a SDS in the same building as the service should ever need an electrode conductor, while we can run branch circuits or feeders to the same location and the EGC is just fine, unless someone in the code making panel believes that lightning knows to only take the path of the GEC and thinks it won't take the path of the EGC, yep its that stupid.

It makes installing a SDS at a remote location in a non steel structure so costly that most will just install it at the main service with a disconnect and run feeders to the sub panel where they need the circuits because then all they need is an EGC.
 
kwired said:
Understandable for a GEC at a service, where is the current going to come from/go to under normal operating conditions for a separately derived system that is installed properly?
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I agree that there should not be any current on the GEC for a SDS as there should not be any parallel paths like there are for the service, but that was part of the panel statement for the rule that says you can't use a single conductor for both purposes.
I guess that the GEC for the SDS would be connected via EGCs to conductive objects that have a path to earth and some of the service grounded conductor current would flow on that path.
 
hurk27 said:
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I have never understood why a SDS in the same building as the service should ever need an electrode conductor, while we can run branch circuits or feeders to the same location and the EGC is just fine, unless someone in the code making panel believes that lightning knows to only take the path of the GEC and thinks it won't take the path of the EGC, yep its that stupid.
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I submitted a proposal a couple of cycles ago to permit exactly that, but CMP5 did not like it...don't remember what their statement was for sure.
 
don_resqcapt19 said:
I agree that there should not be any current on the GEC for a SDS as there should not be any parallel paths like there are for the service, but that was part of the panel statement for the rule that says you can't use a single conductor for both purposes.
I guess that the GEC for the SDS would be connected via EGCs to conductive objects that have a path to earth and some of the service grounded conductor current would flow on that path.
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Any EGC could have unintended current on it, if we really wanted that to stop as well as help eliminate many "stray voltage" issues we would stop using grounded conductors as normal current carrying conductors. But I don't see that happening anytime soon.
 
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