Parallel EGC

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FWIW, my understanding of the change was to permit a single grounding conductor in a cable tray where paralleled tray-cables often have undersized equipment grounds,
(We were told that in an IAEI class.. I have not seen the ROP, etc)
 
charlie b said:

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.
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.​


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Yes, but there is conductors in parallel and there also is paralleling multiple smaller conductors to effectively create one larger conductor. EGC's can not be combined to create an equivalent larger conductor. As already mentioned, if you need 500 kcmil according to 250.122 you can not combine two runs of 250 kcmil to get a 500 equivalent conductor.

infinity said:
All that means is that if you install parallel conductors in a single raceway that you only need one EGC.
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infinity said:
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.
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If you have multiple EGC's in a run for whatever reason, they all must be sized per largest overcurrent device supplying any conductor in the raceway, so again if a 500 kcmil is called for by 250.122, and for whatever reason you did run three EGC's in one raceway they would all need to be 500 kcmil.
 
I hear you all but I do not see anything that states I cannot run 2- 250 kcms in the same conduit in lieu of a 500 kcm. Some are saying that 310.10(H) means ..... but that is not clear in the wording. It is not that I don't believe that you need a single larger conductor but I am not hearing the words say that.
 
Dennis Alwon said:
I hear you all but I do not see anything that states I cannot run 2- 250 kcms in the same conduit in lieu of a 500 kcm. Some are saying that 310.10(H) means ..... but that is not clear in the wording. It is not that I don't believe that you need a single larger conductor but I am not hearing the words say that.
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Let's assume that you can do something like this, please show me where the calculation for for finding the equivalent size of the single EGC is in the NEC.
 
al hildenbrand said:
. . . 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?
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  1. Because the NEC does not say that that shall be permitted.
  2. Because that table assigns the same EGC for a range of OCPD ratings. The table would have to be arranged proportionally, in order for a "half of this yields half of that" rule to work out.
  3. Because the total impedance of two smaller wires, even if they are in parallel and thus have an equivalent impedance of half that of a single conductor, may yet be higher than the desired impedance you would get from one larger wire.
 
kwired said:
If you have multiple EGC's in a run for whatever reason, they all must be sized per largest overcurrent device supplying any conductor in the raceway, so again if a 500 kcmil is called for by 250.122, and for whatever reason you did run three EGC's in one raceway they would all need to be 500 kcmil.
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I have to disagree with this statement. I believe that we can run a pair of #8s protected by a 60 amp breaker and include a #10 EGC in the same conduit as a pair of #12s protected by a 20 amp breaker and include a #12 EGC. The "same size EGC in each conduit" rule has to do with a single circuit that is fed via two or more conduits.

Edited to add: 250.122(C) talks about using the EGC that is sized for the largest OCPD serving any conductor in the raceway. But that refers to a single EGC that serves all circuits in the raceway. If each circuit has its own EGC, then this rule does not come into play.

 
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infinity said:
. . . please show me where the calculation for for finding the equivalent size of the single EGC is in the NEC.
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Dennis Alwon said:
Is there a calculation for the ungrounded conductors?
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While we are on that subject, can anyone point out a statement in the NEC that explicitly states that if you run two conductors in parallel, the total ampacity becomes double that of a single conductor?​

 
charlie b said:
  1. Because the NEC does not say that that shall be permitted.
  2. Because that table assigns the same EGC for a range of OCPD ratings. The table would have to be arranged proportionally, in order for a "half of this yields half of that" rule to work out.
  3. Because the total impedance of two smaller wires, even if they are in parallel and thus have an equivalent impedance of half that of a single conductor, may yet be higher than the desired impedance you would get from one larger wire.
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infinity said:
Let's assume that you can do something like this, please show me where the calculation for for finding the equivalent size of the single EGC is in the NEC.
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Then why can the last sentence of 2017 NEC 310.10(H)(5) allow the summing of the EGC circular mils of multiple cables, cables that can even have EGCs smaller than 1/0?

I submit that this is the guideline for the calculating of smaller parallel EGCs in a single raceway, auxiliary gutter or cable tray.
 
al hildenbrand said:
Then why can the last sentence of 2017 NEC 310.10(H)(5) allow the summing of the EGC circular mils of multiple cables, cables that can even have EGCs smaller than 1/0?
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I can't answer that one just now. I don't have the 2017 handy. The 2014 mentions "sectioned equipment." I don't know what that means.

 
This thread has veered of to a place where it's trying to find words in the NEC do not exist, I'll let you guys hash it out.
 
Here is 310.10

(H) Conductors in Parallel.
(1) General. Aluminum, copper-clad aluminum, or copper
conductors, for each phase, polarity, neutral, or grounded
circuit shall be permitted to be connected in parallel (electrically
joined at both ends) only in sizes 1/0 AWG and larger
where installed in accordance with 310.10(H)(2) through
(H)(6).


Exception No. 1: Conductors in sizes smaller than 1/0 AWG shall be
permitted to be run in parallel to supply control power to indicating
instruments, contactors, relays, solenoids, and similar control devices,
or for frequencies of 360 Hz and higher, provided all of the following
apply:


(a) They are contained within the same raceway or cable.
(b) The ampacity of each individual conductor is sufficient to
carry the entire load current shared by the parallel conductors.
(c) The overcurrent protection is such that the ampacity of each
individual conductor will not be exceeded if one or more of the parallel
conductors become inadvertently disconnected.


Exception No. 2: Under engineering supervision, 2 AWG and 1 AWG
grounded neutral conductors shall be permitted to be installed in parallel
for existing installations.


Informational Note to Exception No. 2: Exception No. 2 can be
used to alleviate overheating of neutral conductors in existing
installations due to high content of triplen harmonic currents.


(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.


(3) 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.


(4) Ampacity Adjustment. Conductors installed in parallel
shall comply with the provisions of 310.15(B)(3)(a).


(5) Equipment Grounding Conductors. Where parallel equipment
grounding conductors are used, they shall be sized in
accordance with 250.122. Sectioned equipment grounding
conductors smaller than 1/0 AWG shall be permitted in multiconductor
cables, if the combined circular mil area of the
sectioned equipment grounding conductors in each cable
complies with 250.122.


(6) Bonding Jumpers. Where parallel equipment bonding
jumpers or supply-side bonding jumpers are installed in raceways,
they shall be sized and installed in accordance with
250.102.
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charlie b said:
I have to disagree with this statement. I believe that we can run a pair of #8s protected by a 60 amp breaker and include a #10 EGC in the same conduit as a pair of #12s protected by a 20 amp breaker and include a #12 EGC. The "same size EGC in each conduit" rule has to do with a single circuit that is fed via two or more conduits.

Edited to add: 250.122(C) talks about using the EGC that is sized for the largest OCPD serving any conductor in the raceway. But that refers to a single EGC that serves all circuits in the raceway. If each circuit has its own EGC, then this rule does not come into play.
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In some instances I see what you are saying. Say you had non metallic raceway ran both circuits to a T conduit body then went separate ways with each circuit - but you aren't tying the two EGC's together other then at the source end so they are not "in parallel".

What I was getting at is if they are "in parallel" they would both need to be sized per the largest overcurrent device involved.

Reality is they might be indirectly in parallel anyway via metal machine or building components, but that happens all the time.
 
charlie b said:
I can't answer that one just now. I don't have the 2017 handy. The 2014 mentions "sectioned equipment." I don't know what that means.
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Here, let me provide a copy.
2017 NEC 310.10(H)(5) Equipment Grounding Conductors. Where paralleled equipment grounding conductors are used, they shall be sized in accordance with 250.122. Sectioned equipment grounding conductors smaller than 1/0 AWG shall be permitted in multiconductor cables, if the combined circular mil area of the sectioned equipment grounding conductors in each cable complies with 250.122.
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al hildenbrand said:
Here, let me provide a copy.
2017 NEC 310.10(H)(5) Equipment Grounding Conductors. Where paralleled equipment grounding conductors are used, they shall be sized in accordance with 250.122. Sectioned equipment grounding conductors smaller than 1/0 AWG shall be permitted in multiconductor cables, if the combined circular mil area of the sectioned equipment grounding conductors in each cable complies with 250.122.
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Seems to be describing a listed cable assembly to me that happens to have the EGC broken up into multiple components - perhaps certain VFD cables would be a good example.
 
than you can run a feeder to a secound building or structure using say two 4/0 direct buried cables in parallel

paralleling the equipment grounds for a 400 amp circuit
 
So if I have a 5000 amp feeder with 12 sets of 700 kcm's many of you think that a 1200 kcm aluminum conductor (Table 250.122) must be pulled in each conduit and not- 2 sets of 600 kcm's. Wow, that would be a nightmare, IMO
 
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