I need a sanity check on using an equipment grounding conductor (EGC) also as a grounding electode conductor (GEC). For example, for a 150A 12kv feeder to a 3000kva 480x277V pad mount transformer feeding a 4000A 480V service, if I size my equipment grounding condutor at 3/0 CU in lieu of #6 CU , could it serve as both the equipment ground and as a grounding electrode conductor and thus bonding both electrode systems together (based on both the 12kv and 480 systems each have their own grounding electodes)? Or would I need to pull separate equipment ground and grounding electrode conductor to bond the systems together?
Use of an EGC as a GEC
- Thread starter Richard S
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ibew441dc
Senior Member
:smile:IMO you have some terms mixed up a bit that are crucial in properly sizing and applying the appropriate rules.
(Paraphrasing) Based on the above you have a 150A 12KV feeder to a 3000kva 480/277V transformer to a 4000A 480V service
That does not make sense to me.....
1) the 150A 12kv feeder is feeding a 3000 KVA transformer(feeder) which is feeding a 4000A 480V feeder,
2)or it is 150A 12KV service supplying 3000 KVA transformer(feeder) feeding a 480/277V feeder
3)or it is a 480/277 volt service that is being supplied by the utility 3000kva transformer (12kv primary/ 480/277v secondary)
Don't take it the wrong :smile:way but failing to present the accurate scenario will make it impossible to accurately answer your question.
A few of questions I would have for you would be...
1) Where is the service point?
2) How did you come up with a 6 AWG EGC?
3) What is the justification of a 3/0 over a 6AWG?
Again don't take this the wrong way, but I recommend visiting article 100 and reviewing , all conductors associated with Service, Feeder, EGC, GEC, and GE.
- Location
- Illinois
- Occupation
- retired electrician
I see no issue using a single conductor for both purposes as long as you meet the installation rules for both. I understand that there is an accepted proposal for the 2011 code that will prohibit this practice.
As Dan said, there appears to be an issue with the terms you used in your question. You can't have a feeder for the primary of the transformer and a service on the secondary side of the transformer.
As Dan said, there appears to be an issue with the terms you used in your question. You can't have a feeder for the primary of the transformer and a service on the secondary side of the transformer.
M. D.
Senior Member
Well this guy thinks it needs to be separate
http://www.mikeholt.com/technical.p...g Electrode Conductor at Transformer (12-7-2K)
I love the way he answered this one ,.. must have been a good day..
http://www.mikeholt.com/technical.p...g Electrode Conductor at Transformer (12-7-2K)
I love the way he answered this one ,.. must have been a good day..
Thanks for your input Dan, I see how I was unclear.
Service point (Utility metering) is at 12kv primary switchgear (PSG). PSG has 3 ea fused load interupter switches that feed 3 ea 3000kva 12kv x 480/277V pad mount transformers that feed 3 ea 4000A 480/277V distribution boards (not services)
I came up with 6 CU AWG EGC for 150A 12kv feeder per 250.122
The 3/0 CU was based on required size of GEC for 3000kva transformers per 250.30(3).
What we would like to accomplish is to efficiently bond each of the grounding electodes present for the building which include 4 separate electrodes for the primary switch gear and each of the 3000kva Transformers. Each of the 3000kva transformers and 4000A distribution boards are located at different areas arround a building where a single grounding grid won't work.
Per 250.50 "All grounding electrodes ... that are present at each building served shall be bonded together to form the grounding electrode system." I didn't see where the code reference necessary size of GEC to accomplish this necessary bonding. This can all be done via feeders from PSG to each of the transformers, but do I need to pull separate EGC and GEC for PSG to each tranformer or would one combined EGC and GEC be sufficient and how to size such combined conductor. Another post with link to a Mike Holt comment disputes the ability to do this.
Appreciate the input
IMO, there is no reason in your installation to even consider doing this.Thanks for your input Dan, I see how I was unclear.
Service point (Utility metering) is at 12kv primary switchgear (PSG). PSG has 3 ea fused load interupter switches that feed 3 ea 3000kva 12kv x 480/277V pad mount transformers that feed 3 ea 4000A 480/277V distribution boards (not services)
I came up with 6 CU AWG EGC for 150A 12kv feeder per 250.122
The 3/0 CU was based on required size of GEC for 3000kva transformers per 250.30(3).
What we would like to accomplish is to efficiently bond each of the grounding electodes present for the building which include 4 separate electrodes for the primary switch gear and each of the 3000kva Transformers. Each of the 3000kva transformers and 4000A distribution boards are located at different areas arround a building where a single grounding grid won't work.
Per 250.50 "All grounding electrodes ... that are present at each building served shall be bonded together to form the grounding electrode system." I didn't see where the code reference necessary size of GEC to accomplish this necessary bonding. This can all be done via feeders from PSG to each of the transformers, but do I need to pull separate EGC and GEC for PSG to each tranformer or would one combined EGC and GEC be sufficient and how to size such combined conductor. Another post with link to a Mike Holt comment disputes the ability to do this.
Appreciate the input
Run an EGC from MV switchgear to transformer and bond to case.
There is no need to run an EGC for secondary side of the transformer as bonding will be taken care of with the grounded conductor (aka neutral). Drive a ground rod at each xfmr and bond it to the neutral. Also bond the neutral to the case. BTW, each xfmr is a separately derived system. At each secondary "distribution" switchgear, make up your local GES and bond it to the neutral or grounding bus, and also install a system bonding jumper. Done.
- Location
- Illinois
- Occupation
- retired electrician
I wish Mike would have cited a code section. I am not aware of any code section that would prohibit a dual use conductor. That is assuming that you can meet the code requirements for both.
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