Parallel EGC

[Dennis Alwon]

If I have to parallel my conductors to be sized at 800 kcm(490 amps). If I want to parallel them I could use 2- 250(255*2=510amps)

Now suppose by equipment grounding conductor in a different example needs to be 500 kcm based on 250.122. Do I use Table 8 and use 2-250 kcm or do I use table 310.15(B)(16) as done above for the ungrounded conductors assuming a 75C rating. Thus 500 kcm(380 amps) so I could use 2- 3/0 (200 *2=400 amps).

I feel I should know this. In this example I want to parallel the equipment grounding conductor in one conduit

 

[david luchini]

In this example I want to parallel the equipment grounding conductor in one conduit

I don't believe that you are permitted to do that. But if you were allowed to parallel the egc, I think it would be based on area...(2)250mcm = (1)500mcm.

 

[augie47]

This help ?

 

[Dennis Alwon]

I don't believe that you are permitted to do that. But if you were allowed to parallel the egc, I think it would be based on area...(2)250mcm = (1)500mcm.

I believe this allows it. And why would it based on area when the ungrounded conductors are not based on area.

(2) Conductor and Installation Characteristics. The paralleled
conductors in each phase, polarity, neutral, grounded circuit
conductor, equipment grounding conductor, or equipment
bonding jumper shall comply with all of the following:
(1) Be the same length.
(2) Consist of the same conductor material.
(3) Be the same size in circular mil area.
(4) Have the same insulation type.
(5) Be terminated in the same manner.

 

[david luchini]

I believe this allows it. And why would it based on area when the ungrounded conductors are not based on area.

I don't see anything in that section that would allow a 500mcm egc to be (2) 250mcm's.

And it would be based on area because T250.122 tells you the minimum size of the egc, not the minimum ampacity of the egc.

 

[augie47]

I don't see that section allowing it... that sections gives you the parameters once the wire size has been selected. The Handbook has an expatiation as to why each has to be full size but its a bit long to post.

 

[infinity]

You cannot use multiple smaller EGC's to make one larger one. T250.122 is for singular conductors without exception to use equivalent parallel conductors.

 

[Dennis Alwon]

I don't see anything in that section that would allow a 500mcm egc to be (2) 250mcm's.

And it would be based on area because T250.122 tells you the minimum size of the egc, not the minimum ampacity of the egc.

But it does state the equipment grounding conductor can be in parallel -- perhaps they mean a full size in each conduit but IMO that is not really parallel

 

[infinity]

But it does state the equipment grounding conductor can be in parallel -- perhaps they mean a full size in each conduit but IMO that is not really parallel

I agree that's what that means, full size in each parallel raceway.

 

[charlie b]

This help ?

Gus, the issue is not what size EGC to put into each parallel conduit. It is about whether two smaller EGCs can be installed in parallel in the same conduit, as a substitute for one larger one.

 

[infinity]

Gus, the issue is not what size EGC to put into each parallel conduit. It is about whether two smaller EGCs can be installed in parallel in the same conduit, as a substitute for one larger one.

I believe that Gus's graphic shows (among other things) that you need a full sized EGC in each raceway.

 

[charlie b]

But it does state the equipment grounding conductor can be in parallel.

Yes, a full size EGC in one conduit can be placed in parallel with a full sized EGC in a second conduit. That is not the same as a smaller size EGC in parallel with another smaller size EGC in the same conduit.

. . . but IMO that is not really parallel

Sure it is. If you take two wires, whatever those wires do for a living, connect their "starting points" to each other, and connect their "ending points" to each other, they are in parallel.​

​

 

[charlie b]

I believe that Gus's graphic shows (among other things) that you need a full sized EGC in each raceway.

Agreed. But that has nothing to do with Dennis' question.

 

[infinity]

Sure it is. If you take two wires, whatever those wires do for a living, connect their "starting points" to each other, and connect their "ending points" to each other, they are in parallel.
​

I agree, but we tend to think of parallel conductors as using more than one smaller conductor to create a large one. I can see how that can be a little confusing when applied to EGC's. As you've stated by definition parallel conductors are connected together at both ends.

 

[charlie b]

And why would it based on area when the ungrounded conductors are not based on area.

Because what matters is impedance. Ampacity depends on "conditions of use." Change the ambient temperature or add more wires to a raceway or put the conduits in an underground ductbank, and you may have a different ampacity. But the impedance of a wire is unaffected by such conditions. (OK, I know that a wire's impedance gets higher with higher temperatures. But in the installation conditions we deal with and the time it takes to clear a fault, that is insignificant.)

 

[al hildenbrand]

In this example I want to parallel the equipment grounding conductor in one conduit

There's a new section in the 2017 NEC, 250.122(F)(1):

2017 NEC 250.122 Size of Equipment Grounding Conductors.
(F) Conductors In Parallel.
(1) Conductor Installation In Raceways, Auxiliary Gutters, or Cable Trays.
(a) Single Raceway or Cable Tray. If conductors are installed in parallel in the same raceway or cable tray, a single wire-type conductor shall be permitted as the equipment grounding conductor. . . .

The single wire "shall be permitted", NOT "shall be installed." To me, this implies that the EGC "shall be permitted" to be installed in parallel in the same raceway or cable tray.

2017 NEC 250.122(F)(1)(a) continues:

2017 NEC 250.122 Size of Equipment Grounding Conductors.
(F) Conductors In Parallel.
(1) Conductor Installation In Raceways, Auxiliary Gutters, or Cable Trays.
(a) Single Raceway or Cable Tray. If conductors are installed in parallel in the same raceway or cable tray, a single wire-type conductor shall be permitted as the equipment grounding conductor. The wire-type equipment grounding conductor shall be sized in accordance with 250.122, based on the overcurrent protective device for the feeder or branch circuit. . .

Going back to 310.10(H), Dennis, your quote of 310.10(H)(2) Conductor and Installation Characteristics. doesn't give the permission to parallel the EGC in a single raceway. Rather, the rule gives the "characteristics" of the installation and conductors.

You have to look down to 310.10(H)(5) and read "Where parallel equipment grounding conductors are used. . . " to read that you already have the permission. IMHO

Certainly, the very title of 2017 NEC 250.122(F)(1) says it all: "Size of EGCs, Conductors in Parallel, Conductor Installation In . . . Single Raceway.)

 

[infinity]

There's a new section in the 2017 NEC, 250.122(F)(1):

The single wire "shall be permitted", NOT "shall be installed." To me, this implies that the EGC "shall be permitted" to be installed in parallel in the same raceway or cable tray.

All that means is that if you install parallel conductors in a single raceway that you only need one EGC.

 

[al hildenbrand]

All that means is that if you install parallel conductors in a single raceway that you only need one EGC.

Ahh, but it DOESN'T say a single EGC is required.

A single EGC is "permitted" in lieu of a paralleled EGC.

 

[infinity]

Ahh, but is DOESN'T say a single EGC is required.

A single EGC is "permitted" in lieu of a paralleled EGC.

If you put three sets of parallel conductors in a single raceway it says that I only need to install one EGC, one can certainly install an EGC for each set if you so choose.

 

[al hildenbrand]

If you put three sets of parallel conductors in a single raceway it says that I only need to install one EGC, one can certainly install an EGC for each set if you so choose.

Now suppose my equipment grounding conductor in a different example needs to be 500 kcm based on 250.122. Do I use Table 8 and use 2-250 kcm or do I use table 310.15(B)(16) as done above for the ungrounded conductors assuming a 75C rating. Thus 500 kcm(380 amps) so I could use 2- 3/0 (200 *2=400 amps).

I feel I should know this. In this example I want to parallel the equipment grounding conductor in one conduit

Dennis wants, in his example, to parallel the EGC, in a single raceway, with two conductors.

Since the size of a single EGC, in a single raceway, is only the Table 250.122 AWG for the rating for the OCPD ahead of the EGC and related conductors, why would one NOT halve the OCPD rating (for two parallel EGCs in a single raceway) and use the corresponding conductor size from Table 250.122?