Parallel Residential Service

[george t. everett]

Table 310.15(B)(6) allows one to use 2/0 copper type THWN-2 for a 200amp underground residential service. Can 2/0 be paralleled for a 400 amp residential service? Does it make a differance if it goes to 2 200amp main disconnects or 1 400 amp main dsiconnect?

 

[charlie b]

Re: Parallel Residential Service

I don?t think so. First of all, I don't see the word "underground" in paragraph 310.15(B)(6). Secondly, I think the code's authors constructed that Table with a specific configuration in mind. But they did not document their thought process in an FPN or in any other way that permits the reader to extend the logic into a different configuration.

For example, you would normally be limited to 175 amps (75C) for a 2/0 copper. If you double that by paralleling two 2/0 cables, you double the 175 to 350, not to 400. This is one of many cases I?ve seen recently in which I would not recommend doing anything that the Tables, Articles, or notes do not explicitly say is acceptable.

 

[pierre]

Re: Parallel Residential Service

George

You can parallel 2/0 cu to 2 - 200 amp panels for a 400 amp service, but to a 400 amp disconnect you need to run 400 cu kcmil. Stating that this is an underground service don't forget about calculating for voltage drop if this is a long run.

Pierre

 

[george t. everett]

Re: Parallel Residential Service

Pierre,

I think I know what you are saying. If I wanted to parallel to a 400 amp disconnect I would need a conductor size of 200kcmil, half of 400kcmil as permitted. This would have to be a 4/0 copper conductor. Is this OK. Thanks for the help!

 

[don_resqcapt19]

Re: Parallel Residential Service

I would permit the parallel 2/0 for a 400 amp dwelling unit service. The table requires 400 kcmil rated at 335 amps for a 400 amp service. 2/0 is 175 amp wire and a parallel set would be good for 350 amps or 15 amps more than the table permitted 400 kcmil.
Don

 

[george t. everett]

Re: Parallel Residential Service

Pierre,

I think I am missing something! 2/0 copper is rated for 175 amps & 400kcmil is rated for 335 amps. Logic would say 2-2/0s would be better. Please educate me.

 

[jro]

Re: Parallel Residential Service

G T Everett, you would parrallel two sets of 2/0 from the pole or xfrm underground in conduit to a 400 amp meter base,to a set of line side double barrel lugs, and then from the load side of the meter base out of your double barrel lugs, take one set of 2/0 conductors to one 200 amp disconnect and the other set of 2/0 conductors to the other 200 amp disconnect. Just make sure to follow the NEC regulations for parrallel conductors NEC 310.4

 

[el santo]

Re: Parallel Residential Service

jro thats how i would do it but wouldnt u use parrallel 3/0 single phase to ur meter base from the pole or xfmr hey can somebody tell me what u use the little faces for

 

[websparky]

Re: Parallel Residential Service

Hi Guys,

IMO;

Please be sure to read NEC 2002 300.3 (B)(1)Paralleled Installations. There are some restrictions!

Also, I have yet to see a meter enclosure rated for 400A. Maybe in my area, they aren't available?
It has been my experience that the largest meter enclosure is 200A.

Hope this helps,
Dave

 

[roger]

Re: Parallel Residential Service

El Santo, look at article 310.15(B)(6) (the table) and cross reference 310.16 to see what everyone is talking about here.

At the bottom left of your post window you will see "Instant Graemlins" these are to help give emotion or feeling to your typed words since it is so hard to express sentiment with letters.

(unless you are someone like Marjorie Kinnan Rawlings )

Roger

 

[el santo]

Re: Parallel Residential Service

web spark man meter bases i have seen them rated for 600 amps the meter it self would not be thats where cts are used to record the electric use

 

[el santo]

Re: Parallel Residential Service

roger man t310.15 b 6 then u can use parrallel 2/0 because this is residential and t310.15 b 6 allows 2/0 to be rated at 200amps is that what u mean roger hey thats

 

[pierre]

Re: Parallel Residential Service

George

For residential single-phase services up to 400 amps, you do not need to reference 310.16. Table 310.15(B)(6) is what I am referencing. 2/0 cu is rated at 200 amps, 400 kcmil is rated 400 amps. The 2 - 200 amp panels in parallel are an equivalent 400 amp service. Since the main in each panel is 200 amps, the 2/0 cu will work. a 400 amp disco needs to be fed with the 400 kvmil.

We use a 400 amp CT-Meter enclosure, Trans S or Trans C. The Trans S is more common. These units are approved by Con Edison - our utility company.
When ordering the Ct cabinets, you would specify if you needed double lugs (for the 2- 200 amps) or single for the 400 kcmil.
Does this help?

Pierre

 

[el santo]

Re: Parallel Residential Service

pierre man i think u and jro are right and i agree with u 2

 

[george t. everett]

Re: Parallel Residential Service

Pierre, This morning I spoke to a inspector from The N.Y.B.F.U. and to parallel a 400amp underground residential service, I would have to run 4/0 copper from pole or transformer to meter cabinet. I could run 2/0 copper to each 200 amp disconnect. The line side is a true parallel run, the load side is not. This kinda makes sense to me. The 4/0 is run to get the 400kcmil which is required by table 310.15(B)(6). Does this sound right to you? Thanks

 

[jro]

Re: Parallel Residential Service

George T, why would you have to use 4/0 copper if 2/0 copper, according to NEC table 310.15 (B) (6), is rated for 200amps in a residential application, if any thing 3/0 copper parrallel would be ok, it is rated for 200amps at 75 degree NEC Table 310.16.

 

[george t. everett]

Re: Parallel Residential Service

Table 310.159(B)(6) says 400kcmil for 400 amp, to get equivalent to 400kcmil you would need to run 4/0 copper. Thats the way I am being told.

 

[don_resqcapt19]

Re: Parallel Residential Service

George,
I think that you should compare the conductors based on the ampacity and not the cross sectional area. If the 2/0s are in 2 conduits they would have an ampacity of 350 amps. 400 kcmil only has an ampacity of 335 amps. If you are putting the parallel conductors in the same raceway, you will have to derate and in that case 3/0s in parallel in a common conduit have an ampacity of 360 amps after applying the 80% factor. This is clearly equivalent to the ampacity of a 400 kcmil.
Don

 

[george t. everett]

Re: Parallel Residential Service

Don, I agree with what you are saying, but the inspectors are telling me that the cross sectional area has to be met to comply with table 310.15(B)(6). Its seems to me if 2/0 is good for 200 amp, That 2-2/0 is good for 400. The service conductors will be direct buried if that makes a differance.

 

[pierre]

Re: Parallel Residential Service

George

Did you ask the inspector where he was referencing from in the NEC? Also ask him to cite to you in the code where he is deriving his calculations from, the NYBFU is supposed to do this.
The procedure I explained to you is approved by inspectors in our area. Where are you located in NY? Just a question, I am not going to cause trouble for you.

Of course I am assuming that you are using 2, 200 amp main disconnect type panels for your parallel service.
If you like, you can send me a private message if you need more info.

Pierre