# 310.15(B)(6) vs IRC E3603.1



## jar546 (Jul 15, 2013)

Situation for debate:  (hopefully we can all sort this out as I am a bit confused by language and intent)

A 200A service is installed on a single family dwelling.  The UG or AG service feeds a 200 combo meter base with disco/panelboard on the outside.

From there it feeds a 200 panel inside the home that supplies 100% of the loads of the dwelling.

The EC runs 2/0 copper from the main disco to the interior sub feed which again, serves 100% of the loads in the dwelling.

So far so good because Table 310.15(B)(6) says we can reduce the conductors to 2/0 copper(IRC= Table E3603.1).  This would normally be 3/0 copper for a commercial establishment.

Now the question becomes this:

If the electrician utilizes the exterior main disco/panel for any other purpose and installs an OCPD in it for another circuit, the interior panel is no longer serving "all" loads of the dwelling and the reduction in 310.15(B)(6), (IRC E3603.1)no longer applies, does he have to change the size of the service wire or feeder?

Where it gets confusing is the fact that the language in both section states



> The feederconductors to a dwelling unit shall not be required to have an
> 
> allowable ampacity greater than that of the service-entrance
> 
> conductors that supply them.


So, can 310.15(B)(6) & E3603.1 apply to the service conductors from the weather head to the main disco if the main and sub panel share the loads of the dwelling?

You can thank Chris Kennedy for this one as he discovered a problem on a recent field trip we were on.


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## Dennis (Jul 15, 2013)

IMO, the 2/0 is legal to the first disconnect and 3/0 would be required to the interior even though a load has been removed from the interior panel.  It is one of those anomalies.

Now 215.2(A)(4) as quoted above seems to come into play and many people believe it says that the 3/0 should not be required since it should not have to be larger than the service conductors.

Here is how I see it.  The ampacity does not have to be greater than the service conductors.  So what is the ampacity of 2/0 on a residence for the service--- 200 amps.  Now what is the ampacity of 3/0 when pulled to the sub panel when other loads are taken from the service-- T.310.16 says 200 amps.  So it is not a higher ampacity although the wire is larger.

I believe in the 2014 art. 215.2(A)(4) will be gone


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## raider1 (Jul 15, 2013)

Dennis said:
			
		

> IMO, the 2/0 is legal to the first disconnect and 3/0 would be required to the interior even though a load has been removed from the interior panel.  It is one of those anomalies.Now 215.2(A)(4) as quoted above seems to come into play and many people believe it says that the 3/0 should not be required since it should not have to be larger than the service conductors.
> 
> Here is how I see it.  The ampacity does not have to be greater than the service conductors.  So what is the ampacity of 2/0 on a residence for the service--- 200 amps.  Now what is the ampacity of 3/0 when pulled to the sub panel when other loads are taken from the service-- T.310.16 says 200 amps.  So it is not a higher ampacity although the wire is larger.
> 
> ...


Correct, because Table 310.15(B)(7) (2011 NEC) will also be gone and replaced with a permitted reduction instead of a Table.

Chris


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## jar546 (Jul 15, 2013)

If this were an underground service where the POCO provides the lateral, and it was a combo meter/panelboard, then technically there is no service cable that is provided for and installed by the electrician so 3/0 would have to be installed at a minimum IF there were to be breakers in the exterior combo panelboard.


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## gfretwell (Jul 15, 2013)

The way I read this thread, I would say the SE to the house was OK with the reduced size but the SE from the disconnect up to the service point would need to be full size since that segment was not just the dwelling load.

It does bring up the question of whether everything on a single family property would be considered dwelling load tho.

IE, if we fed a spa from the house panel, it is clearly dwelling load but if we put the same spa on that disconnect away from the home, is it still dwelling load?

As a related question, my house is fed from a main panel in a detached garage. Is that service entrance from the service head a 310.15(B)(6)? Is the feeder to the house from the garage a 310(B)(6)?


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## Dennis (Jul 15, 2013)

gfretwell said:
			
		

> The way I read this thread, I would say the SE to the house was OK with the reduced size but the SE from the disconnect up to the service point would need to be full size since that segment was not just the dwelling load.


  If the cable to the meter is power company's then the nEC has no say in the matter.  If it is the ec's then yes (B)(7) would apply





> It does bring up the question of whether everything on a single family property would be considered dwelling load tho. IE, if we fed a spa from the house panel, it is clearly dwelling load but if we put the same spa on that disconnect away from the home, is it still dwelling load?


  There was an addition in the 2008 I believe that stated dwelling units and related structures but I don't have time to check what it is related to-- I am cooking...





> As a related question, my house is fed from a main panel in a detached garage. Is that service entrance from the service head a 310.15(B)(6)? Is the feeder to the house from the garage a 310(B)(6)?


  IMO the feeder to the house from the garage could be based on (B)(7)


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## jar546 (Jul 16, 2013)

I'm still in the 2008 with my B(6) and you fancy guys are in your 2011.  I can't even think about 2014 since we are still in the 08.


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## north star (Jul 16, 2013)

*= % =*

Does anyone actually know when the `14 NEC will be out ?....I am needing to upgrade on the Handbook as well !

*% = %*


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## chris kennedy (Jul 16, 2013)

north star said:
			
		

> *= % =*Does anyone actually know when the `14 NEC will be out ?....I am needing to upgrade on the Handbook as well !
> 
> *% = %*


I pre-ordered and they ship in September.


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## jar546 (Jul 16, 2013)

In PA at our IAEI meetings a few years ago we bought the 2011 and started training on it to prepare for the 2011 to go in effect for 2013 (we have a 2 year lag due to the 1 year lag on the I-Codes in PA) but, in true PA fashion, they decided to skip 2012 I-Codes so we will have the 2008 until well past the time the 2014 comes out.  My biggest issue was using the new windmill section since I have done a bunch of these under the 05 and 08.  Finally got a windmill section that I cannot use at all.

OK, no thread drift.................what am I doing?

Back on topic.

So under the 08 & 011 with an underground service provided by the POCO, the 3/0 would be required for the feeder to the sub if the combo meter/panel had a circuit installed but with an OH service, the feeder would be OK to stay at 2/0 because the SE conductors were able to stay 2/0.  Is that what I am getting from you guys?


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## Dennis (Jul 16, 2013)

I don't know why you think there is a difference between the overhead and underground.  If the contractor installs overhead or underground then they must follow the NEC.   Some areas the electrical contractor is responsible for the underground so I want that clarified.

IMO, If there is a circuit in the first disconnect then the wire to the sub panel would need to be 3/0.  I think that is bogus but that is how I interpret it and I explain why in my first post.  Not everyone agrees with that and some think that 2/0 is all that is needed.


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## chris kennedy (Jul 16, 2013)

The install we looked at has a POCO supplied UG service lateral making the 'service point' the line side lugs of the meter in the meter/main combo. From the load side of meter is bussing to the main 200A main breaker. So the 'service conductors' are not a wire type. Had this been overhead the EC supplies the riser conductors and POCO supplies the drop.


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## jar546 (Jul 16, 2013)

chris kennedy said:
			
		

> The install we looked at has a POCO supplied UG service lateral making the 'service point' the line side lugs of the meter in the meter/main combo. From the load side of meter is bussing to the main 200A main breaker. So the 'service conductors' are not a wire type. Had this been overhead the EC supplies the riser conductors and POCO supplies the drop.


Yes, absolutely.  Here is a quick review and update:

This is a 200A single phase 120/240 service for a single family dwelling.

The service lateral conductors are supplied by and installed by the POCO.  It is an UG installation.

The POCO service laterals land inside the combo box on the exterior which consists of a meter and main disco/panelboard seen below.  (cont.....below picture)







This exterior disco acts as the main disco for the house.  Fed from the load side of this disconnect is a pane inside the garage of the SFR.  It also supplies the buss for the available breaker spaces that you see above.

The electrician ran 2/0 copper feeders (except for neutral of course) to the panel in the garage.

It is my understanding that when an OCPD is placed in this exterior panelboard for a circuit, the feeders to the other panelboard no longer serve all of the circuits of the dwelling, therefore 310.15(B)(6) of 2008, 310.15(B)(7) of 2011 does not apply and the conductors must be 3/0.

The service entrance conductors are the bars that connect the load side of the meter with the line side of the main disconnect outside.  There are no wire conductors for service conductors since the POCO provides those laterals and only God will know what size they will be.

Palm Beach County has notified me that they do not enforce that rule for any feeders inside the dwelling per their electrical AHJ.


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## chris kennedy (Jul 16, 2013)

jar546 said:
			
		

> Palm Beach County has notified me that they do not enforce that rule for any feeders inside the dwelling per their electrical AHJ.


I would be very interested in seeing PBC's written amendment.


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## jar546 (Jul 17, 2013)

chris kennedy said:
			
		

> I would be very interested in seeing PBC's written amendment.


Is one required in Florida when a municipality removes a code requirement?


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## Dennis (Jul 17, 2013)

jar546 said:
			
		

> This exterior disco acts as the main disco for the house.  Fed from the load side of this disconnect is a pane inside the garage of the SFR.  It also supplies the buss for the available breaker spaces that you see above.
> 
> The electrician ran 2/0 copper feeders (except for neutral of course) to the panel in the garage.
> 
> ...


This could be looked at differently.  If the service riser is the responsibility of the contractor and he puts 3/0 to the meter then IMO if the garage is detached then he would only need 2/0 into the house since that wire supplies the total load to the dwelling.  (B)(7) would not apply to the service conductors since they serve the house and another structure.  It is really how the ahj looks at it


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## jar546 (Jul 17, 2013)

Dennis said:
			
		

> This could be looked at differently.  If the service riser is the responsibility of the contractor and he puts 3/0 to the meter then IMO if the garage is detached then he would only need 2/0 into the house since that wire supplies the total load to the dwelling.  (B)(7) would not apply to the service conductors since they serve the house and another structure.  It is really how the ahj looks at it


yes, but, the facts are that this is a SFR with a built in garage, not detached and the panel in the garage supplies 100% of the load for the entire home until a breaker is added in the exterior panel for another dwelling circuit.


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## gfretwell (Jul 17, 2013)

I have still not heard why the feeder would ever need to be larger than the SE.

"The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors."


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## chris kennedy (Jul 17, 2013)

Who is saying they need to be ???


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## jar546 (Jul 17, 2013)

gfretwell said:
			
		

> I have still not heard why the feeder would ever need to be larger than the SE."The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors."


the service-entrance conductors are metal bars directly connected to the load side of the meter.  They are not wires.  That was explained, hence this issue.  I could probably put 250MCM in and be the equivalent of those bars.


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## Dennis (Jul 17, 2013)

jar546 said:
			
		

> yes, but, the facts are that this is a SFR with a built in garage, not detached and the panel in the garage supplies 100% of the load for the entire home until a breaker is added in the exterior panel for another dwelling circuit.


  Agreed..  I was thinking detached


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## Dennis (Jul 17, 2013)

gfretwell said:
			
		

> I have still not heard why the feeder would ever need to be larger than the SE."The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors."





			
				chris kennedy said:
			
		

> Who is saying they need to be ???


I did n a sense.  I said the ampacity does not need to be larger however what is the conductor size for a residential 200 amp service--- 2/0 copper...310.15(B)(7) or (B)(6) for 2008

Now if 310.15(B)(7) is not allowed to be used as in a feeder that does not supply the entire load then what is the conductor size for the 200 amp sub panel--- 3/0.  Although the wire is larger the ampacity of the conductor is not.   I stated this in my first post.


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## Gregg Harris (Jul 17, 2013)

Proposal to Change 2011 NEC

6-49a Log #CP604 NEC-P06 Final Action: Accept

(310.15(B)(7))

________________________________________________________________

TCC Action: The Correlating Committee directs that the panel clarify their action on this proposal.

   The Correlating Committee also directs the panel to revise the Informational Note as it contains permissive language, i.e. the word “may”.

   This action will be considered as a public comment.

Submitter: Code-Making Panel 6,

Recommendation: Delete Table 310.15(B)(7) and replace 310.15(B)(7) with the following:

   (7) 120/240 Volt, Single-Phase Dwelling Services and Feeders. For service and feeder conductors of 120/240-volt, single-phase, individual dwelling unit one-family, two-family, and multifamily service ratings from 100 through 400 amperes, an adjustment factor of 0.83 of the service ampere rating shall be permitted to be used to determine the size of the ungrounded conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided that the requirements of 215.2, 220.61, and 230.42 are met.

   Informational No. 1: The conductor ampacity may require other correction or adjustment factors applicable to the conductor installation.

   Informational No. 2: See example DXXX in Annex D.

Substantiation: It was determined that during the 1956 Proceedings of the Sixteenth NFPA Annual Meeting that 84 percent was used to establish the aluminum residential service conductor size. However, if the panel used 84 percent in the changed language, it would have resulted in larger sizes for some of the conductors, compared to the sizes in the 2011 NEC. Since the panel had no technical substantiation to justify these changes, 83 percent was used to maintain consistency with the sizes in the 2011 Table 310.15(B)(7).

   In order to address the various proposals submitted suggesting changes to 310.15(B)(7), the panel analyzed the existing language and determined that the conductor sizes in Table 310.15(B)(7) are equivalent to those that would be used if a 0.83 multiplier was applied to each service ampere rating. The resulting conductor size will be the same as existing text in Table 310.15(B)(7), if the same conductor types and installation conditions are applied.

   The informational note was added to make it clear that adjustment and correction factors apply depending on conditions of use. This action no longer requires the definition of a “main power feeder” in 310.15(B)(7).

Panel Meeting Action: Accept

Number Eligible to Vote: 10

Ballot Results: Affirmative: 9 Negative: 1

Explanation of Negative:

   WALL, C.: Removal of the table does not add clarity or usability to the NEC.

Comment on Affirmative:

   CLINE, S.: This proposal is the result of many, many hours of panel member time over many code cycles. It is intended to clearly and easily express the ongoing intent of the panel over these many code cycles of misinterpretation. This wording gives a simple “duty cycle” type adjustment which, through a simple mathematic multiplication, yields a minimum ampacity requirement for conductor sizing. Hopefully the twelve submitters who also spent their time trying to resolve the misunderstandings will be satisfied with this result.

   It recognizes the long-known diversity of load for this exact class of load. It recognizes that conditions of installation may also affect the ampacity of the conductor. It recognizes that feeders, only if sized in relation to the service rating, may safely be allowed the same diversity adjustment since they are either carrying 100% of the diversified load, OR only loads too small to change the effective diversity have been removed ahead of the feeder, OR large enough loads have been removed ahead of the feeder to make the 17% adjusted ampacity a moot point. The concerns about increased dwelling loads in general is addressed in 230.79 where the service rating amperage itself is determined.

   It should now be clear that while feeders may also use the diversity adjustment, it must be based on the 230.79 service rating, not the size of the OCPD for the feeder. If you run a 200 amp feeder from a 200 amp rated service, you get to use the adjustment, start with a 166 minimum ampacity conductor, apply any other required adjustments, and choose your conductor. If you run a 100 amp feeder from a 200 amp rated service, you still get use the adjustment, but of course the 166 minimum ampacity conductor then required might not be an advantage over the normal 100 amp conductor. You may not use 100 amps (the feeder OCPD size) to apply the adjustment to - you must use the service rating.

   Separate issue No. 1:

   Please note: I believe that the following editorial changes to the new wording recommendation of 6-49a need to be made for the publications of the ROP and Draft.

   Final Edited wording:

   (7) 120/240-Volt, Single-Phase Dwelling Services and Feeders. For service and feeder conductors of 120/240-volt, single-phase, individual dwelling units of one-family, two-family, and multifamily service ratings of 100 through 400 amperes, 83 percent of the 230.79 service ampere rating shall be permitted to be used as the minimum ampacity to determine the size of the ungrounded conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided that the requirements of 215.2, 220.61, and 230.42 are met.

   Informational Note No. 1: The conductor ampacity may require other correction or adjustment factors applicable to the conductor installation.

   Informational Note No. 2: See example DXXX in Annex D.

   Editorial changes to be considered (in order of occurrence):

   (Legislative text will not paste into this comment area.)

   1) change “an adjustment factor of 0.83” to “83 percent”

Examples elsewhere in the code (within text sentences as opposed to within Tables), such as 310.60©(2)(b), 430.122(A), 630.31(A)(1), etc, utilize the percentage wording. It is consistent with existing NEC usage.

   2) add “230.79” in front of “service ampere rating”

Direct reference to the NEC source of the “Service Rating” amperage value.

   3) add “as the minimum ampacity” before “to determine”

To proactively state the mathematically obvious result of scientific units which results from the multiplication of the service rating (amps) times 0.87 (87%), and that it is a minimum number still subject to the other adjustments of 310.15(B).

   Separate issue No. 2:

   I believe that an Informational Note No. 3, showing a restructured form of the 2011 NEC Table 310.15(B)(7), would be very helpful as a transition from Table to adjustment factor.

The title and title heading would be unused. Only the portion of the existing Table 310.15(B)(7) below the double line would be used, and one column heading must be edited:

   “Informational Note No. 3: Partial listing of conductor AWG or kcmil sizes for 310.15(B)(7) applications, showing only 75°C (167°F) conductors, under conditions of installation which do not require any other adjustments.”

The heading of the first column would need to have “or Feeder” deleted since the relationship is always to the “Service Rating” even for feeders. It should read “Service Rating (Amperes)” - OR it should read “230.79 Service Rating (Amperes)” if the addition of “230.79” within the body of the 310.15(B)(7) text is approved.

   The rest of the Table could be used as-is.

   “AWG or kcmil” is used purposefully in the note to avoid the ambiguity of the word “size” as it relates to conductors. Does “size” mean “physical size” or “ampacity”?

   I believe that in general the unqualified word “size” should not be used anywhere in the code in reference to conductors. “AWG or kcmil size” or “ampacity” would be unambiguous terms.

   Separate issue No. 3:

   I recommend another Informational Note:

“Informational Note No. 4: Section 310.15(B)(7) excludes 208Y/120-Volt supplied systems (single or three phase) due to the additional heat from the presence of a third conductor carrying current.”

   I realize that the NEC is not a design manual, but this issue is so often misunderstood that it seems worth the print space to help assure that AHJs have proper and easy tools to use, and to help avoid repeated proposals and comments.

   KENT, G.: This proposal is correct as a Reject, however, I disagree that permission exists in the code to allow this type of wiring.

   LAIDLER, W.: I’m voting to accept the proposal. I would also recommend that the editorial changes recommended by NFPA staff be incorporated into the proposal (as stated below).

(7) 120/240-Volt, Single-Phase Dwelling Services and Feeders. For service and feeder conductors of 120/240-volt, single-phase, individual dwelling units of one-family, two-family, and multifamily service ratings of 100 through 400 amperes, 83 percent of the 230.79 service ampere rating shall be permitted to be used as the minimum ampacity to determine the size of the ungrounded conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided that the requirements of 215.2, 220.61, and 230.42 are met.

   Informational Note No. 1: The conductor ampacity may require other correction or adjustment factors applicable to the conductor installation.

   Informational Note No. 2: See example DXXX in Annex D.

   These recommended changes will provide better clarity for the user on how to apply this new language.


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## gfretwell (Jul 17, 2013)

jar546 said:
			
		

> the service-entrance conductors are metal bars directly connected to the load side of the meter.  They are not wires.  That was explained, hence this issue.  I could probably put 250MCM in and be the equivalent of those bars.


Article 100 disagrees with that



> The service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop.


There are several replies up thread that imply the feeder beyond that disconnect with another load attached must be 310.16, not 310.15(B)(6).


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## Span (Jul 17, 2013)

IMO 200A panel can not sub to another 200A sub-panel.

1. No slot at main able to accomandate another 200A breaker, lower A maybe.

2. 2/0 feeder bending radius.

If they realley need 200A to house, use meter socket instead of meter panel at garage then 2/0 to main panel at house, and have another feeder or sub to garage. Will this way aceptable?


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## Dennis (Jul 18, 2013)

Span said:
			
		

> IMO 200A panel can not sub to another 200A sub-panel. 1. No slot at main able to accomandate another 200A breaker, lower A maybe.
> 
> 2. 2/0 feeder bending radius.
> 
> If they realley need 200A to house, use meter socket instead of meter panel at garage then 2/0 to main panel at house, and have another feeder or sub to garage. Will this way aceptable?


That is not correct.  There are feed thru lugs on some 200 amp panels.  In this setup you do not add a 200 amp breaker but instead you are using the main breaker as the lugs are attached to the buss.

You are correct in that many panels will not allow more than 110 amps or so across any stab.  This is not the case with all panels especially the meter main panels.


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## gfretwell (Jul 19, 2013)

I have a QO 150a in my garage panel that grabs 8 slots. I think they also make that in 200


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## jar546 (Jul 19, 2013)

gfretwell said:
			
		

> There are several replies up thread that imply the feeder beyond that disconnect with another load attached must be 310.16, not 310.15(B)(6).


Is that your opinion too?

What is the general consensus?


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## gfretwell (Jul 19, 2013)

If you can (and do) use 310.15(B)(6) for the service, you should never need bigger wire anywhere on that service. That is how I read the first paragraph.


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## Dennis (Jul 19, 2013)

gfretwell said:
			
		

> If you can (and do) use 310.15(B)(6) for the service, you should never need bigger wire anywhere on that service. That is how I read the first paragraph.


It seems like we are still caught up on the bigger wire rather than a higher ampacity.  Either no one understands what I have been saying or you all think I am nuts.

Okay

You run 3/0 copper to a panel next to the meter.  Short nipple from meter to service panel.  3/0 @75C is rated 200 amps.  Not a problem.  Now I run 3/0 copper ser cable from the main panel to the sub panel 50 feet away.  I go thru a crawl space and up thru the bottom plates.  Now SER is rated 75C if it is not run in insulation and there is no caulk in the hole where you come up from the crawl area.  Since we must caulk that hole the SER is now rated 60C.  3/0 SER cable at 60C is rated 165 amps.  Now it is no longer and good for 200 amps so we must use 4/0 as long as the load is not greater than 195 amps.

So when you say it never has to be bigger that is not always the case.  This is why I pipe all my 200 amp panels if possible.


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## jwelectric (Jul 19, 2013)

We are allowed diversity when doing a service calculation that we are not allowed when doing a remote panel calculation.

In a dwelling the service will never see the total calculated load but it is possible to have a remote panel loaded to the full amount of the rating.

When the NEC addresses the feeder as outlined in this thread then the remote panel could have a full load even in the scenario outlined in the original post therefore the feeder conductor must be sized to the calculated load.

In the case of the feeder of the dwelling unit all one has to do is protect the feeders by 240.4(B)

See 215.3

Once we leave the service overcurrent device then the feeders must comply with 240.4(B) as far as the overcurrent protection


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## peach (Jul 20, 2013)

we are still under 2005 (having recently crawled from 1996), and will only be going as far as 2011 any time soon (probably next year).

Since the POCO can deliver 200 amp using #2 if they chose to (and we can't tell THEM that they are wrong - perish the thought), I'm guessing the meter must transform power somehow.  Look up at a service entrance from the transformer once.

I will boot this over to my senior electical inspector (hub/selectric from the old BB) for his consideration.


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