1200 amp 120/240 Residential Service

[Daetiogar]

OK...
We are wiring a 1200 amp service in a RESIDENTIAL single family dwelling.

We are planning on running 3 sets in parrell and we ending up in a great debate...

According to 240.40(C) the wiring being protected by our 1200 amp breaker "...shall be equal to or greater than the rating of the overcurrent device defined in 240.6"

Which tell us we need to run 3 sets of 600 kcmill for the load of a 1200 amp breaker. The counter argument giving to us was in 310.15(B)(6) which points us to the table 310.15(B)(6) saying that 400 kcmill can feed 400 amps which gave the interpretation of 3 sets of 400 kcmill = 1200 amp

which is correct or are we both wrong?

 

[iwire]

In my opinion the way 310.15(B)(6) and the table is written it cannot be used as basis for parallel conductors.

However one of the other moderators has posted some information from the code making panel members that shows they feel 310.15(B)(6) can be used for parallel conductor sizing.


In any event I am very sure 3 sets of 400 would not be overloaded.

 

[charlie b]

The counter argument giving to us was in 310.15(B)(6) which points us to the table 310.15(B)(6) saying that 400 kcmill can feed 400 amps which gave the interpretation of 3 sets of 400 kcmill = 1200 amp

I don't think the debate can be settled here, for you are likely to get at least two viewpoints on the question.

My viewpoint is that the table does not say that the ampacity of a 400 MCM, under the conditions of use as described in the table and the related text, is 400 amps. The word "ampacity" does not appear in the table. What the table says is that if the service or feeder is 400 amps, then you can use a 400 MCM. It does not go on to say that you can parallel a set of three 400's to get an "ampacity" of 1200, since again it does not use the word "ampacity," nor does it say that a 1200 amp service or feeder can be fed via three sets of 400's. It says what it says, and it doesn't tell us how to extend its reasoning beyond the actual values as shown in the table. Therefore, I side with the group who say you need a set of three 600's.

Now let us see how many other viewpoints appear.

 

[charlie b]

In any event I am very sure 3 sets of 400 would not be overloaded.

I agree with this.

However one of the other moderators has posted some information from the code making panel members that shows they feel 310.15(B)(6) can be used for parallel conductor sizing.

I don't know if that was me who posted that information. But it might have been. One of my proposals for the 2011 NEC was intended to clarify that you cannot use the posted values as though they were ampacity values, so as to justify parallelling conductors. The CMP rejected my proposal, and stated that they disagreed with my interpretation that parallel conductors were beyond the scope of the table. I haven't seen how the 2011 is worded, so I don't know if they made any related changes at all.

 

[Daetiogar]

I haven't seen how the 2011 is worded, so I don't know if they made any related changes at all.

I checked in the 2005 2008 and 2011 the phrasing is the same in all... baring the relocation of the table desgination

 

[iwire]

I was actually thinking of Don, I am pretty sure he posted some CMP statements.

 

[adelle]

Any residence owner that requires a 1200a service should not have to worry about the price difference between 400 and 600mcm :roll:

 

[Daetiogar]

HAHA truth but the word budget has been used a lot in this 20,000 sq ft house... in any event I will run what ever I am told too run, I just want to know if I was right with my 600 kcmill call or if they are right with the 400 kcmill call. An inspector who I know personally says 600s too but its seems to be one of those questions I get 20 differnent people all saying different things.

 

[don_resqcapt19]

From the ROP for the 1996 code.

6-74- (Article 310, Notes to Ampacity Tables of 0 to 2000 Volts, Note 3):
SUBMITTER: R.W. Worthing, Auberry, CA
RECOMMENDATION: Add new text at the beginning of the second sentence to read:
Application of this Note shall not be permitted for conductors connected in parallel.
SUBSTANTIATION: At a recent Section meeting of the IAEI, the question of the applicability of Note 3 to parallel conductors was raised. No consensus was established. Actions, by CMP 6, whether in acceptance or rejection of this Proposal, will establish, for the record,the position of the Panel.
PANEL ACTION: Reject.
PANEL STATEMENT: Conductors 1/0 and larger are permitted to be paralleled by Section 310-4. This would apply to Note 3.
NUMBER OF PANEL MEMBERS ELIGIBLETO VOTE: 10
VOTE ON PANEL ACTION:
AFFIRMATIVE: 10

 

[steve66]

FWIW, Charlie, I would of agreed with you. Especially since 800 amps seems to be a cutoff point where we aren't allowed to use a breaker rating that is even slightly above the wire rating. So why should be assume a table that only goes to 400 amps can be extended to 1200 amps?

However, looking at the table makes me wonder - is the OP really going to have a 1200 amp single phase service? Will the POCO provide that?

If its a 3 phase service, the table wouldn't apply.

240V, 1200A, 1 phase just happens to turn out to be almost exactly the same KVA rating as 208V, 800 amps, 3 phase.

Steve

 

[Daetiogar]

So in your opinion you think that 400 kcmill in parallel is fine? part of the reason it is single phase is the local power authority cl and p ( Conn light and power ) will not provide 3 phase to residential dwellings

 

[don_resqcapt19]

From the ROC

6-32 - (Article 310, Notes to Ampacity Tables of 0 to 2000 Volts, Note 3): Reject
SUBMITTER~ Jim Pauley, Square D Company
COMMENT ON PROPOSAL NO: 6-74
RECOMMENDATION: The Panel should Accept this proposal in Principle by action on 6-77 and 6-73a.
SUBSTANTIATION: The action on 6-73a incorporated the wording suggested by 6-77. This proposal clearly was intended to keep conductors in Note 3 from being used in parallel. The revision to the table heading is completely accurate and necessary. We are not dealing with conductor ampacity in this section, We are dealing with service/feeder ratings. In the 1990 NEC the table headings clearly indicated that the ampacity column in the table was for a service size and not for a conductor ampacity. The change of the heading in '93 to "Rating in Amps" seems to imply that the conductor is rated at this value and was interpreted that it could be paralleled (I disagree with this interpretation). The accepted wording of "Service or Feeder.Rating" will again clearly imply that you find your needed service or feeder rating in the right column and the conductor sizes sbown in that row are permitted to be used for that rating. No basis or method for paralleling two 4/0 AI conductors is given in the
table. If the Panel agrees that this paralleling is still OK, I must be able to parallel two 600Kcmil aluminum conductors for an 800A dwelling service as well. Obviously the Panel has had no substantiation to permit this practice.
PANEL ACTION: Reject..
PANEL STATEMENT: The service or feeder ratings in the tabular portion of Note 3 are permissible current radngs for the wire sizes indicated, similar to the allowable ampacities permitted in Table 310-16 through Table 310-19. Table 310-16 is used for paralleling conductors; likewise, Note 3 to these same tables permits paralleling
of conductors in accordance with Section 310-4.
NUMBER OF PANEL MEMBERS ELIGIBLE TO VOTE: 10
VOTE ON PANEL ACTION: AFFIRMATIVE: 10

 

[Dennis Alwon]

IMO, 1200 amps is not listed for residential in 310.15(B)(6) therefore you cannot apply this table. The table is only good to 400 amps and I also believe that parallel conductors are not an option. I vote 600 kcm.