mbrooke
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- United States
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- Technician
I need a sanity check, when paralleling wire there will be times when I need a full size EGC, correct?
Parallel Wire Size
- Thread starter mbrooke
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
Each EGC needs to be sized as if it was the only one.
mbrooke
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Suspected such. If I decide to do a 4000 amp feeder in 4/0 sets, I can get away with a 4/0 EGC, correct?
Carultch
Senior Member
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- Massachusetts
You use the same EGC size that you would use, as if it weren't paralleled. One EGC per raceway (or otherwise per wiring structure), full size as if it were the only EGC. The EGC's then get paralleled themselves at both ends. Unlike parallel conductors in general that require a minimum of 1/0 in order to parallel, it is OK to have any size EGC's in parallel. There will be circuits for which the EGC size ends up being just as large as the ungrounded conductors, if you have a circuit with a lot of sets in parallel.
250.122(A) indicates that EGCs never have to be larger than the circuit’s ungrounded conductors. So yes it is correct.
You probably won't find 4000A equipment that is built for 18 sets of 4/0 in parallel, so it is an unlikely example. A more likely example is 12 sets of 400 kcmil on a 4000A circuit, with the 400 kcmil EGC.
250.122(A) indicates that EGCs never have to be larger than the circuit’s ungrounded conductors. So yes it is correct.
You probably won't find 4000A equipment that is built for 18 sets of 4/0 in parallel, so it is an unlikely example. A more likely example is 12 sets of 400 kcmil on a 4000A circuit, with the 400 kcmil EGC.
mbrooke
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Alright, thanks! 
- Location
- Illinois
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- retired electrician
No...full sized in each raceway based on the 4000 amp OCPD. CMP 5 is on record saying that the size of the circuit conductors for a parallel system is the sum of all of the conductors connected in parallel and it is not the size of the ungrounded conductors in each raceway.
You need a 500 kcmil EGC in each raceway for that system, no matter what size the ungrounded conductors are in each raceway.
mbrooke
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mbrooke
Batteries Included
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Can you elaborate more on this or link to it? I'm a bit confused by this statement. I'm reading it to take the EGC as part of that sum... however I can't see the EGC being larger than the current carrying conductors in any given conduit.
packersparky
Senior Member
- Location
- Wisconsin
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- Inspector
The size of the ungrounded conductors in this case would be the the size of all of one set of parallel conductors. 18 x whatever kcmil size 4/0 is.
mbrooke
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Basically the mm2 of a single equivalent conductor divided to the number of sets?
packersparky
Senior Member
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- Wisconsin
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- Inspector
Let's say I want to use 3 sets of 600 kcmil copper for a 1200 amp feeder. The size of the ungrounded conductor is 1800 kcmil.
Carultch
Senior Member
- Location
- Massachusetts
The sizes of the ungrounded conductor add up to 1800 kcmil, but isn't 1800 kcmil itself. The size of the ungrounded conductor per set, is still 600 kcmil.
winnie
Senior Member
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- Springfield, MA, USA
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- Electric motor research
I think this might be a case of invoking Charlie's rule and that what the code _says_ might be different from what the code making panel wants it to say.
The code says that the EGC does not need to be larger than the ungrounded conductors.
One can easily interpret this to mean no larger than the individual wires making up the ungrounded conductors.
I personally agree with CMP 5's interpretation as reported by don_resqcapt19. Given that any given _single_ EGC might be called to carry the fault supplied by _all_ of the ungrounded conductors in parallel, the rule that each EGC be full sized makes sense to me. In particular look at the wording in 310 where we have the rules for parallel conductors: 'electrically joined at both ends to form a single conductor'. So other portions of the code support sets of wires joined at both ends being treated as a 'single conductor'.
But the code says what it says.
-Jon
- Location
- Illinois
- Occupation
- retired electrician
CMP 5 says that for a parallel circuit the size of the ungrounded conductor is the sum of the areas of the conductors connected in parallel.
Not going to take the time needed to research all of the ROPs and ROCs to find the statement. You can find PDFs of the 2014 and older codes on the NFPA website and the 2017 and 2020 stuff is there too, but in a different format.
There were a couple of PIs on this issue for the 2023 code, and the panel statements will be easy to find when the First Draft Report is published on 7/2/21.
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