Article 250.122(F)

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Dale001289

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Georgia
Article 250.122(F), 2014 NEC: Let’s say I have 4parallel circuits, consisting of single conductors, triangular configuration installed in cable tray (see exhibit 392.4, NEC Handbook); do I need an individual EGC, (sized per Table 250.122),in each set of the four parallel circuits, or can use 1 EGC to suffice for all four sets?
 

Carultch

Senior Member
Location
Massachusetts
Article 250.122(F), 2014 NEC: Let’s say I have 4parallel circuits, consisting of single conductors, triangular configuration installed in cable tray (see exhibit 392.4, NEC Handbook); do I need an individual EGC, (sized per Table 250.122),in each set of the four parallel circuits, or can use 1 EGC to suffice for all four sets?

Each conduit or wiring structure requires a full sized EGC. I see a single cable tray as a single wiring structure, and thus requiring only 1 EGC for all four sets.
 

Dale001289

Senior Member
Location
Georgia
more on Parallel Circuits and EGC's

more on Parallel Circuits and EGC's

I see an issue with the 'one EGC for all four sets' philosophy. Art 300.3 (B) describes how all conductors, including the EGC, must be containedwithin the same raceway or cable or heat will increase as well asimpedance. Each set of 'parallels' represents a cable; thus if a single EGC is routed externally to 3 of the 4 sets, the low-impedance/low heat benefit isreduced.
 

david luchini

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Connecticut
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I see an issue with the 'one EGC for all four sets' philosophy. Art 300.3 (B) describes how all conductors, including the EGC, must be containedwithin the same raceway or cable or heat will increase as well asimpedance. Each set of 'parallels' represents a cable; thus if a single EGC is routed externally to 3 of the 4 sets, the low-impedance/low heat benefit isreduced.


300.3(B) says all conductors shall be contained within the same raceway, auxilliary gutter, CABLE TRAY, cablebus assembly, trench, cable or cord...
 

Dale001289

Senior Member
Location
Georgia
300.3(B) says all conductors shall be contained within the same raceway, auxilliary g

300.3(B) says all conductors shall be contained within the same raceway, auxilliary g

It also says CABLE - one does not preclude the other, at least that's the way I see it - the physics don't change when it comes to heat and impedance.
 

david luchini

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Connecticut
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It also says CABLE - one does not preclude the other, at least that's the way I see it - the physics don't change when it comes to heat and impedance.

You didn't describe a situation with cables...you described individual conductors installed in a cable tray. Only one EGC is required to comply with 250.122.

You could run parallel sets in a single conduit, and only one EGC would be required.
 

Dale001289

Senior Member
Location
Georgia
250.122(F) 2002 NEC

250.122(F) 2002 NEC

You didn't describe a situation with cables...you described individual conductors installed in a cable tray. Only one EGC is required to comply with 250.122.

You could run parallel sets in a single conduit, and only one EGC would be required.



2002 NEC: 250.122(F) “Conductors in Parallel. Whereconductors are run in parallel in multiple raceways or cables as permitted in310.4, the equipment grounding conductors, where used, shall be run in eachraceway or CABLE…”
Clearly the 2002 code had it right. What happened? Did they decide to skip the physics and theIEEE Green Book and go with their 'gut' feeling?
 

GoldDigger

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Placerville, CA, USA
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If you have multiple bundles in parallel in the cable tray, that does not make them separate cables. It is necessary to bundle all CCCs into each bundle, but no great harm in separating the EGC which carries only fault current.
If you want to include a fractional size EGC in each bundle I see no reason not to do that either.
 

david luchini

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Location
Connecticut
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Engineer
2002 NEC: 250.122(F) “Conductors in Parallel. Whereconductors are run in parallel in multiple raceways or cables as permitted in310.4, the equipment grounding conductors, where used, shall be run in eachraceway or CABLE…”
Clearly the 2002 code had it right. What happened?Did they decide to skip the physics and theIEEE Green Book and go with their 'gut' feeling?

The installation you describe does NOT have conductors run in parallel in multiple raceways or cables.

The section you reference would not have applied to your installation in 2002.
 

Dale001289

Senior Member
Location
Georgia
If you have multiple bundles in parallel in the cable tray, that does not make them separate cables. It is necessary to bundle all CCCs into each bundle, but no great harm in separating the EGC which carries only fault current.
If you want to include a fractional size EGC in each bundle I see no reason not to do that either.


I disagree with "no harm in separating the EGC" - yes, the EGC only carries fault current, but a fault focused on bundles 1, 2 or 3 would react differently than a fault focused on bundle 4, that is, if bundle 4 carried the lone EGC. As far as a 'fractional size EGC in each bundle' - what would be the guideline for sizing this if not T250.122?
 

Dale001289

Senior Member
Location
Georgia
You didn't describe a situation with cables...you described individual conductors installed in a cable tray. Only one EGC is required to comply with 250.122.

You could run parallel sets in a single conduit, and only one EGC would be required.


David: parallel circuits in a single conduit would only need ONE EGC because a low impedance path for all current carrying conductors would exist - due proximity of magnetic flux between phases. This is not the same when parallel conductors are separated, as in cable tray applications.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
I disagree with "no harm in separating the EGC" - yes, the EGC only carries fault current, but a fault focused on bundles 1, 2 or 3 would react differently than a fault focused on bundle 4, that is, if bundle 4 carried the lone EGC.
Say that's true. Is it going to make enough difference to affect how the OCPD operates? The consensus as expressed in the NEC is no.

Cheers, Wayne
 

Dale001289

Senior Member
Location
Georgia
There is nothing giant in it.

Using one full sized EGCs in a cable tray is safe, compliant and nothing to worry about.

Feel free to link us to the articles describing the problems it causes.

Code Panels are obviously confused on this topic since earlier versions (2002, e.g.) made no mention whatsoever of the one EGC per tray scenario.
As far as links as to why each bundle should have its own EGC, see IEEE Green book and do a search.

"one of the marks of true manhood is admitting you are wrong" - Dale
 
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