Looking for confirmation on Neutral sizing

s-park-er

Member
Location
Oroville, CA
Occupation
Building mechanic - specialty problem-solver.
I just want to confirm before pulling...
This project is interesting and keeps getting more so - the owner is an impulse buyer of building materials; he finds great deals but not always what is needed, so he modifies the plan to accommodate sometimes. Here's the latest. POCO drop is at roadside, 400A to two 200's (house and shop). House is 250ft pull in 3" PVC. at the start he told me that he has 4/0 wire to pull to the house panel (which we will be changed for the correct one for those who saw my last post). I assumed copper, but I was wrong!:eek: So, after convincing him that we cannot use the aluminum as he planned, we looked at options. Buying new copper $$$$$ yikes!! Buying the correct size AL $$$$ also yikes! but alas, he has PLENTY of the Al 4/0; Thousands of feet!!! Sooooo.... we are going to pull parallels of that and call it good.

I'd just like to be certain of my assumption that we can use a SINGLE 4/0 AL for the grounded circuit conductor (neutral) Quick load calcs come up with ~~133A, with 200A OCPD at each end, and we will be using #2CU EGC (which he found somewhere for a deal...)

Thanks in advance, you all are great!!
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Look at 250.122(B)... If you upsize the conductors then you must proportionately upsize the equipment grounding conductor.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
What is wrong with 4/0 Al to a 200A panel? A utility wouldn't even use that large of a conductor for a 250' run. I've got about that length to my house and the utility is half #2 Al (overhead) and half 1/0 Al (buried) for a 200A service.
 
What is wrong with 4/0 Al to a 200A panel? A utility wouldn't even use that large of a conductor for a 250' run. I've got about that length to my house and the utility is half #2 Al (overhead) and half 1/0 Al (buried) for a 200A service.
Yeah not sure exactly what the setup is, if its a 400 A feeder or 2-200's, same pipe or separate.....but yeah about 200-250 feet is where I change from 4/0 to 250 AL for residential. Not sure why everyone puts disconnects with their 320 meter bases....run it as a service using the exception i stayed before and save a bunch of wire and extraneous equipment.
 

s-park-er

Member
Location
Oroville, CA
Occupation
Building mechanic - specialty problem-solver.
Yeah not sure exactly what the setup is, if its a 400 A feeder or 2-200's, same pipe or separate.....but yeah about 200-250 feet is where I change from 4/0 to 250 AL for residential. Not sure why everyone puts disconnects with their 320 meter bases....run it as a service using the exception i stayed before and save a bunch of wire and extraneous equipment.
For clarity, service entrance conductors are dropped to the meter panel at the roadside. Two 200 amp breakers supply circuits that exit there and go in separate 3" pipes, one to the house (250 ft. total), and one for the future shop (not yet sited or built). There is a Christy box in the run where the shop and house pipes depart from each other.
All lookup tables and calculators I used all say 250mcm AL, and the AHJ agrees as well (I did not ask him about the neutral at that time, but I thought it would be appropriate).
In looking at table 250.102(C)(1), two 4/0 = 423200 cmils. AL or CCA over 250 up to 500, would require minimum 1/0AL. 1/0 would be more than adequate for the 133A load calc. Am I not applying this correctly?
@Dennis Alwon , "Proportionally" upsizing the conductor would bring us back to the table mentioned above, no? A 4/0 AL neutral should be more than enough I would think.
Just want to be sure I am interpreting this code correctly...

Thanks again all!!!
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
The neutral or grounded conductor can be as small as the equipment grounding conductor required for the feeder as long as it is big enough for the calculated load.

If what I said above is true then you would have to calculate the cm difference between what you would need to what is compliant. So if 250kcm is the minimum required then you must find the equipment grounding conductor needed for 200 amps --#4 alum then multiply the cm of the #4 by the ratio of the 2 x 4/0 cm / 250 kcm.

A #1 would be needed in each run for the equipment grounding conductor.

For a feeder I don't believe you can use 250.102(C)(1) but 1/0 would work.

215.2(A)(2) Grounded Conductor. The size of the feeder circuit
grounded conductor shall not be smaller than that required by
250.122, except that 250.122(F) shall not apply where grounded
conductors are run in parallel.
Additional minimum sizes shall be as specified in
215.2(A)(3) under the conditions stipulated.
 
Last edited:

Mr. Serious

Member
Location
Oklahoma, USA
Occupation
Electrical Contractor
I just ran these calculations recently, for an estimate for a very similar job (although I didn't buy the wire before I had the job).

My results from my recent calculation: 2 parallel 4/0 for the hots, a single 250kcmil for the neutral, and a #2 for the ground. Design ampacity was 200 for the hots, about 170 for the neutral (or 150, I can't remember which). So, if you used a single 4/0 instead of 250, 133 sounds reasonable for its ampacity. And, I have no doubt that Dennis' calculation in reply #8 is correct, so if you upsize the hot wires to 4/0, the ground wire proportionally upsized should be #1. I would have made a mistake running it with #2.
 

s-park-er

Member
Location
Oroville, CA
Occupation
Building mechanic - specialty problem-solver.
Thanks all for your kind input. As it turns out, the owner-builder of this project; the hoarder of all sorts of building materials; who is a chronic auctioholic, also had acquired a couple of spools of 2/0 AL wire, so we used that for the equipment grounding conductor, saving him >$1000 on copper!
 

retirede

Senior Member
Location
Illinois
Thanks all for your kind input. As it turns out, the owner-builder of this project; the hoarder of all sorts of building materials; who is a chronic auctioholic, also had acquired a couple of spools of 2/0 AL wire, so we used that for the equipment grounding conductor, saving him >$1000 on copper!

Adding “auctioholic” to my vocabulary!
 
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