gec routing

[mcelweec@gmail.com]

i have two seperately derived systems each with four parallel sets of conductors located 200ft from a building.Is it permissible to run the gec to the common grounding point with one of the parallel sets from each "sds",I can't see anything in the code book which allows or disallows this method.

 

[chris kennedy]

Is it permissible to run the gec to the common grounding point with one of the parallel sets from each "sds",

You can't run it in 1 of 4.

310.4(C)

 

[raider1]

You can't run it in 1 of 4.

310.4(C)

310.4(C) would not apply to a GEC, but it would apply to an EGC.

Chris

 

[mcelweec@gmail.com]

Each set will have an egc with one set carrying the additional gec.

 

[benaround]

i have two seperately derived systems each with four parallel sets of conductors located 200ft from a building.Is it permissible to run the gec to the common grounding point with one of the parallel sets from each "sds",I can't see anything in the code book which allows or disallows this method.

The GEC only needs to run to the closest building steel for each SDS.

 

[raider1]

Each set will have an egc with one set carrying the additional gec.

The SDS's would be separate structures and need their own grounding electrode systems installed at each SDS. Take a look at 250.50 and 250.32(A).

Chris

 

[chris kennedy]

310.4(C) would not apply to a GEC, but it would apply to an EGC.

Chris

I beg to differ. I don't believe one of the four conduits can have an extra conductor.

(C) Separate Cables or Raceways. Where run in separate cables or raceways, the cables or raceways with conductors shall have the same number of conductors and shall have the same electrical characteristics. Conductors of one phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor shall not be required to have the same physical characteristics as those of another phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor to achieve balance.

 

[raider1]

I beg to differ. I don't believe one of the four conduits can have an extra conductor.

Good point, I got so involved in the GEC VS EGC thought that I didn't think about the fact that adding a GEC to a single conduit of a parallel installation would still violate 310.4(C).

Chris

 

[augie47]

I guess I may be having a brain cloud here, but if it's a SDS feeding another building, could you not just establish your grounding electrode system at the building wihout a gec from the SDS ?

 

[mcelweec@gmail.com]

These are standby generators with main breakers,I can establish a GES using re-bar and if necessary a ground rod.However according to 250.30(4)do I need to connect both generator GEC's to the common building electrode system.

 

[Pierre C Belarge]

These are standby generators with main breakers,I can establish a GES using re-bar and if necessary a ground rod.However according to 250.30(4)do I need to connect both generator GEC's to the common building electrode system.

Are the transfer switches for the generators 4-pole or 3-pole?

 

[mcelweec@gmail.com]

4 pole transfer switches, they are down stream from em switchgear with a tie breaker.

 

[Pierre C Belarge]

I hope you do not mind, but one more question.

Why are the generators so far from the buildings they are supplying?

 

[Twoskinsoneman]

You know that section says taps off of a common system shall be permitted. I don't see where it says it is required.... Am I missing that?

 

[mcelweec@gmail.com]

The reason they are so far away is both for noise and the parking spots the landlord was willing to give up." Twokinsman" you make a good point,but are these generator enclosures considered seperate structures.

 

[raider1]

but are these generator enclosures considered seperate structures.

I would say yes, the NEC definition of structure is "That which is built or constructed".

Chris

 

[mcelweec@gmail.com]

So in the in the case my re-bar and ground rod would be considered my grounding electrodes? on another note,am I correct in saying that any neutral from my two SDSs and utility cannot be solidly connected as i also see issues with the set-up of the emergency switchgear.

 

[Pierre C Belarge]

Also, do not forget about 700.12(B)(6) or 701.11(B)(5) or 702.11...

 

[mcelweec@gmail.com]

had a better look at the job today and found the neutral in the emergency sw gear common to both generators,however the neutral from the utility is isolated through the 4-pole transfer switches.Can I use 250.30(a)(1) exception 1 and bond both systems in the em switch gear leaving the neutrals isolated at the generators even though Im downstream of the ocpd.The em gear consists of 2 main breakers(one for each generator)with a main tie breaker and a solidly bolted neutral.

 

[RUWired]

had a better look at the job today and found the neutral in the emergency sw gear common to both generators,however the neutral from the utility is isolated through the 4-pole transfer switches.Can I use 250.30(a)(1) exception 1 and bond both systems in the em switch gear leaving the neutrals isolated at the generators even though Im downstream of the ocpd.The em gear consists of 2 main breakers(one for each generator)with a main tie breaker and a solidly bolted neutral.

MC, article 250.30(A)1 requires the bonding jumper be made at the source up to the first OCPD. If the gensets have OCP, thats where the jumper goes.

The exception that allows the common output to be bonded applies to SDS's the are duel fed. This exception would not apply to your generators.

Rick