SFD Service for 2014

[1793]

I just finished a Continuing Education class that covered some of the changes in the 2014 Edition of the NEC. We are currently under the 2011 edition and are due to adopt the 2014 this July.

According to the Instructor Table 310.15(B)(7) has been removed and the verbiage in 310.15(B)(7)(1)-(4) which says the conductor "shall be permitted to have an ampacity not less than 83% of the Service rating."

So, a new 200A service would need to have a #3/0 CU conductor instead of the before allowed #2/0 CU.

100A would now be a #2.

Is this correct?

Thanks

 

[infinity]

According to the Instructor Table 310.15(B)(7) has been removed and the verbiage in 310.15(B)(7)(1)-(4) which says the conductor "shall be permitted to have an ampacity not less than 83% of the Service rating."

So, a new 200A service would need to have a #3/0 CU conductor instead of the before allowed #2/0 CU.

What is 83% of 200 amps? Wouldn't that be your minimum conductor size? Still #2/0 for 200 amps.

 

[1793]

What is 83% of 200 amps? Wouldn't that be your minimum conductor size? Still #2/0 for 200 amps.

83% of 200 is 166 using 2/0 is good for 175A at 75deg and according to 240.6 175 is a standard size breaker so I cannot upsize to 200.
yes / no

 

[infinity]

83% of 200 is 166 using 2/0 is good for 175A at 75deg and according to 240.6 175 is a standard size breaker so I cannot upsize to 200.
yes / no

I see your point, sorry I didn't do the calculation first before posting. This seems to be going in the wrong direction.

 

[infinity]

I thought that the proposal was to keep the existing conductor sizes intact just change from a table to a calculation. :?

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).

 

[augie47]

Allow a little more fuel on the fire.
For the last two or three Code cycles we have had this big albatross hanging abound our neck concerning 338.10(4)(a).
Without Table 310.15(B)(7) are we now back to the ampacity of SE cable when installed in insulation will be the 60? rating. The removal of 310.15(B)(7) seems to have us relying totally on conductor ampacity.

 

[texie]

I thought that the proposal was to keep the existing conductor sizes intact just change from a table to a calculation. :?

It does. It is a little confusing. What it is saying is that you only need 83% of ampacity for given service size. For example, a 200 amp service only needs a conductor ampacity that is 83% of 200. In other words you need an ampacity of 166 amps which is 2/0 CU @75 degree. This makes it work out to the same values as the old table.
The reason for this change is to account for ampacity adjustments to conductors that may be required that the old table did not address.

 

[texie]

Allow a little more fuel on the fire.
For the last two or three Code cycles we have had this big albatross hanging abound our neck concerning 338.10(4)(a).
Without Table 310.15(B)(7) are we now back to the ampacity of SE cable when installed in insulation will be the 60? rating. The removal of 310.15(B)(7) seems to have us relying totally on conductor ampacity.

Yes, I agree. We will have to look at the ampacity before applying the 83%. That will lead to some differences in some applications from the old table.

 

[texie]

augie,
To illustrate your Art 338 concern, this is something we have discussed in our organization.

For example, the typical 4/0 AL SE cable used under the 2011 code would be allowed for 200 amp even in insulation as 310.15(B)(7) said you could. It made no mention of adjusted ampacity.

Under the 2014 code that same 4/0 AL SE in insulation will have to be considered at 60 degree before applying the rules of 310.15(B)(7). So, for a 200 amp service (or feeder) needing an ampacity of 166 amp the 4/0 AL SE will not work as it only has an ampacity of 150 @60 degrees. You will then need a 250 AL SE cable.

I think this is going to be a big issue for many.

 

[1793]

It does. It is a little confusing. What it is saying is that you only need 83% of ampacity for given service size. For example, a 200 amp service only needs a conductor ampacity that is 83% of 200. In other words you need an ampacity of 166 amps which is 2/0 CU @75 degree. This makes it work out to the same values as the old table.
The reason for this change is to account for ampacity adjustments to conductors that may be required that the old table did not address.

We can only up size to the NEXT standard size OCD. In this case 2/0 @ 75 degree is 175A, which is the next standard breaker, so a 200A breaker cannot be used. I have not found anything in print that states we can up-size past the 175A.

Table 310.15(B)(7) being removed only complicates things. While the intent may be as follows:

"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."

but the above, red, is not spelled out in the 2014 book.

 

[texie]

We can only up size to the NEXT standard size OCD. In this case 2/0 @ 75 degree is 175A, which is the next standard breaker, so a 200A breaker cannot be used. I have not found anything in print that states we can up-size past the 175A.

Table 310.15(B)(7) being removed only complicates things. While the intent may be as follows:

"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."

but the above, red, is not spelled out in the 2014 book.

You are misunderstanding 310.15(B)(7). This has nothing to do with the next size up OCD rules. It is telling you that if you meet the conditions of 310.15(B)(7) then you can have a conductor ampacity of not less than 83% of the OC device.
Back to my example for a 200 amp service: 83% of 200 is 166. You then choose a conductor with an ampacity of 166 amps. A 2/0 CU conductor @75 degree has an ampacity of 175 amps. This is more than 166, so it meets the requirements and can be used on a service with an OC device of 200 amps.

 

[texie]

but the above, red, is not spelled out in the 2014 book.[/QUOTE]

Yes it is....310.15(B)(7) (1) and (2). This language just replaces the old table with a formula.

 

[infinity]

It does. It is a little confusing. What it is saying is that you only need 83% of ampacity for given service size. For example, a 200 amp service only needs a conductor ampacity that is 83% of 200. In other words you need an ampacity of 166 amps which is 2/0 CU @75 degree. This makes it work out to the same values as the old table.
The reason for this change is to account for ampacity adjustments to conductors that may be required that the old table did not address.

Thanks for clearing that up.

 

[1793]

You are misunderstanding 310.15(B)(7). This has nothing to do with the next size up OCD rules. It is telling you that if you meet the conditions of 310.15(B)(7) then you can have a conductor ampacity of not less than 83% of the OC device.
Back to my example for a 200 amp service: 83% of 200 is 166. You then choose a conductor with an ampacity of 166 amps. A 2/0 CU conductor @75 degree has an ampacity of 175 amps. This is more than 166, so it meets the requirements and can be used on a service with an OC device of 200 amps.

After a night of sleep and thinking, I do not yet have a hard copy of 2014, I follow what you are saying.

but the above, red, is not spelled out in the 2014 book.

Yes it is....310.15(B)(7) (1) and (2). This language just replaces the old table with a formula.[/QUOTE]

I think it was a mistake to remove Table 310.15(B)(7). This new wording is going to cause some unnecessary confusion. :?

 

[augie47]

I don't have a copy of the 2014 as of yet. Is there anything in Art 338 that opened a door to allow us to use a 4/0AL at mandatd the 60? rating. (B)(7) used to give us that door.

 

[texie]

After a night of sleep and thinking, I do not yet have a hard copy of 2014, I follow what you are saying.



Yes it is....310.15(B)(7) (1) and (2). This language just replaces the old table with a formula.

I think it was a mistake to remove Table 310.15(B)(7). This new wording is going to cause some unnecessary confusion. :?[/QUOTE]

The reality here is that as long as there are no ampacity adjustments required and you are using 75 degree conductors the old table will still work out to the 83%. I suspect that a lot of people will be pasting in the old table for reference.

The issue comes though when you need to make ampacity adjustments for, say, SE cable in insulation as it wiould have to be considered at the 60 degree value. Then you will have to do the calculations and the answer will not be the same as the table. This was the whole point of removing the table and replacing it with a calculation in order to make an ampacity calculation based on the installation conditions. Under the old rules there was no ampacity adjustments, it just simply said use XXX size conductor regardless of conditions.

But I agree that this will take some getting used to for many and many are not going to like the calculated answer when ampacity adjustments are made.

 

[1793]

I think it was a mistake to remove Table 310.15(B)(7). This new wording is going to cause some unnecessary confusion. :?

The reality here is that as long as there are no ampacity adjustments required and you are using 75 degree conductors the old table will still work out to the 83%. I suspect that a lot of people will be pasting in the old table for reference.

The issue comes though when you need to make ampacity adjustments for, say, SE cable in insulation as it wiould have to be considered at the 60 degree value. Then you will have to do the calculations and the answer will not be the same as the table. This was the whole point of removing the table and replacing it with a calculation in order to make an ampacity calculation based on the installation conditions. Under the old rules there was no ampacity adjustments, it just simply said use XXX size conductor regardless of conditions.

But I agree that this will take some getting used to for many and many are not going to like the calculated answer when ampacity adjustments are made.

I think you and I are now on the same sheet of music. It has been a good discussion and one that I think will be had again across the country over the next few months.

 

[infinity]

Just my 2 cents, this type of change just makes it unnecessarily more confusing for the everyday code user. :rant:

 

[1793]

Just my 2 cents, this type of change just makes it unnecessarily more confusing for the everyday code user. :rant:

...and I would like to add that Inspectors are going to have a field day with this. :?:?:?:?