Parallel Conducotrs and its corresponding ground conductor

[JBUDA54]

We have multiple feeders from a piece of SWGR to multiple SWBDs. These feeders are 1600A’s each so we are running parallel feeders using a separately run #4/0 AWG Ground. The Contractor wrote an RFI in order to try a save the owner money and requested that we run a single ground cable for the multiple feeders and tap off the single ground into the SWBDs instead of running individual grounds back to the SWGR. His justification was that it met Article 250.122 (c). My initial thought was that this is something that can save money and seems to make sense in doing as such. I believe that further down in that article in 250.122 (f) for parallel feeders it points to article 310.10(h) and stipulates that the parallel feeder (phase, neutral, and ground) must adhere to 310.10 (h) (2) which says it must have the same length, consist of the same material, be the same size, have the same insulation, and be terminated in the same manner. This reads to me that the contractor’s suggestion is not allowed because the same length and circular mill, and being terminated in the same manner would not be satisfied.


Am I reading the code properly or is this not it’s intent?

 

[GoldDigger]

Please use the term Equipment Grounding Conductor (EGC) instead of just "ground". I will avoid all sorts of ambiguities and complications. :happyyes:

Also note that the NEC will from time to time refer to "ungrounded circuit conductors" (hot) and "grounded circuit conductors" (usually neutral but may be corner ground of delta or just grounded wire of a single ended single phase circuit.) Neither of these includes the EGC, which is not considered a "circuit conductor" since it does not carry current under normal conditions.

That said, the presence or absence of an EGC (wire or raceway) associated with a set of circuit conductors could be considered as affecting the physical and electrical environment of the circuit conductors, but only in the event of a fault.

So it is at least in part an AHJ interpretation whether the proposed EGC arrangement is allowed.
Note also that each conductor set within a parallel setup must have a "full sized" EGC associated with it if a wire EGC instead of a raceway EGC is used.

 

[JBUDA54]

Please use the term Equipment Grounding Conductor (EGC) instead of just "ground". I will avoid all sorts of ambiguities and complications. :happyyes:

Also note that the NEC will from time to time refer to "ungrounded circuit conductors" (hot) and "grounded circuit conductors" (usually neutral but may be corner ground of delta or just grounded wire of a single ended single phase circuit.) Neither of these includes the EGC, which is not considered a "circuit conductor" since it does not carry current under normal conditions.

That said, the presence or absence of an EGC (wire or raceway) associated with a set of circuit conductors could be considered as affecting the physical and electrical environment of the circuit conductors, but only in the event of a fault.

So it is at least in part an AHJ interpretation whether the proposed EGC arrangement is allowed.
Note also that each conductor set within a parallel setup must have a "full sized" EGC associated with it if a wire EGC instead of a raceway EGC is used.

Thank you for your response and please accept my apologies for not using the EGC. I am still not sure if you are agreeing or disagreeing with the interpretation. The contractor is proposing that a full size ground be run but is taking the 250.122 (c) in that they would like to run a single ECG for all of the parallel feeders and then tap the ECG as it drops into each SWBD. I believe that this violates 310.10(h)(2) but I am not fully convinced that this is the code's intent.:?

 

[ron]

Thank you for your response and please accept my apologies for not using the EGC. I am still not sure if you are agreeing or disagreeing with the interpretation. The contractor is proposing that a full size ground be run but is taking the 250.122 (c) in that they would like to run a single ECG for all of the parallel feeders and then tap the ECG as it drops into each SWBD. I believe that this violates 310.10(h)(2) but I am not fully convinced that this is the code's intent.:?

250.122(C) says the single EGC needs to be in the same raceway, cable or tray. Will the paralleled runs all be in a single raceway, cable or tray?

 

[don_resqcapt19]

What wiring method is being used for the feeder cables?

 

[charlie b]

I don't quite understand what the contractor is suggesting. But I believe that 250.122(C) will not get them what they want. Suppose I run a single conduit from a branch circuit panel to a junction box. Inside that one conduit, I run conductors for three separate circuits. I run a pair of #12's for a 20 amp circuit, a pair of # 10's for a 30 amp circuit, and a pair of #4s for a 70 amp circuit. In the junction box, I separate the three circuits and run them to their respective loads. Those three circuits, if run separately, would need EGCs of sizes 12, 10, and 8 respectively. 250.122(C) says you can use a single EGC in the one conduit with all three circuits, but that one EGC has to be sized for the highest rated circuit. It has to be a #8. I don's see your situation as being related to this scenario in any way.

If I were to design a 1600 amp feeder, it would have 5 conduits, each carrying 400 KCMIL ungrounded conductors and a 4/0 EGC. If you have, for example, four switchboards, then you would have 20 conduits, and 20 EGCs each sized at 4/0. How does this relate to what your contractor is suggesting?

 

[JBUDA54]

250.122(C) says the single EGC needs to be in the same raceway, cable or tray. Will the paralleled runs all be in a single raceway, cable or tray?

Yes they will be in the same tray dropping out to their respective SWBDs.

 

[JBUDA54]

I don't quite understand what the contractor is suggesting. But I believe that 250.122(C) will not get them what they want. Suppose I run a single conduit from a branch circuit panel to a junction box. Inside that one conduit, I run conductors for three separate circuits. I run a pair of #12's for a 20 amp circuit, a pair of # 10's for a 30 amp circuit, and a pair of #4s for a 70 amp circuit. In the junction box, I separate the three circuits and run them to their respective loads. Those three circuits, if run separately, would need EGCs of sizes 12, 10, and 8 respectively. 250.122(C) says you can use a single EGC in the one conduit with all three circuits, but that one EGC has to be sized for the highest rated circuit. It has to be a #8. I don's see your situation as being related to this scenario in any way.

If I were to design a 1600 amp feeder, it would have 5 conduits, each carrying 400 KCMIL ungrounded conductors and a 4/0 EGC. If you have, for example, four switchboards, then you would have 20 conduits, and 20 EGCs each sized at 4/0. How does this relate to what your contractor is suggesting?

The feeders will all be run in a commonf cable tray and drop out the their respective SWBD.

 

[JBUDA54]

What wiring method is being used for the feeder cables?

They are running 4 sets of 3/C 500s (1200A feeder) and running a #4/0AWG EGC tapping the single EGC for the multiple set of feeders dropping into each respective SWBD via conduit. There is one 1600A feeder that is running 5 sets of 500s 3/C and also using a #4/0 separate EGC.

My apologies for not making that clear in the original post.

 

[don_resqcapt19]

They are running 4 sets of 3/C 500s (1200A feeder) and running a #4/0AWG EGC tapping the single EGC for the multiple set of feeders dropping into each respective SWBD via conduit. There is one 1600A feeder that is running 5 sets of 500s 3/C and also using a #4/0 separate EGC.

My apologies for not making that clear in the original post.

Assuming that is in cable tray, the 2017 code will permit a single EGC in the tray.

(2) Multiconductor Cables.
(a) If multiconductor cables are installed in parallel, the equipment grounding conductor(s) in each cable shall be connected in parallel.
(b) If multiconductor cables are installed in parallel in the same raceway, auxiliary gutter, or cable tray, a single equipment grounding conductor that is sized in accordance with 250.122 shall be permitted in combination with the equipment grounding conductors provided within the multiconductor cables and shall all be connected together.
(c) Equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)(1)(c). Cable trays complying with 392.60(B), metal
raceways in accordance with 250.118, or auxiliary gutters shall be permitted as the equipment grounding conductor.
(d) Except as provided in 250.122(F)(2)(b) for raceway or cable tray installations, the equipment grounding conductor in each multiconductor cable shall be sized in accordance with 250.122 based on the overcurrent protective device for the feeder or branch circuit.

There has been some debate on this issue under the rules found in the 2014 NEC, without a consensus conclusion. Some say you can do what it now permitted in the 2017, and others say that you need a full size EGC in each cable.
In my opinion, even under the new rule in the 2017 code, the fact that conduit is used between the cable tray and the equipment is a deal breaker. In my opinion that conduit requires a full size EGC in the cables.