Does 310.15(B)(7) apply to 120/208v 1ph dwellings and does it supersede 338.10(B)(4)?

[jhall]

I have a PE on one of my projects that has stated 310.15(B)(7) is not applicable to 120/208Volt dwelling services. He has also asserted that 338.10(B)(4) requires the 60degree ampere rating. Therefore the 2/0 SER Alum I planned to use which is feeding 150amp load centers in each apartment must now be 4/0 SER Alum.
In the past, I have never had anyone question the voltage rating when using Note 3 to table 310.16 or 310.15B7.

Can anyone tell me if the NEC addresses this specifically? Or can you provide some article that may help explain the table's relevance?
Thank you

 

[infinity]

You cannot use 310.15(B)(7) for 208/120 volt systems:

Table 310.15(B)(7) Conductor Types and Sizes for
120/240-Volt, 3-Wire, Single-Phase Dwelling Services and
Feeders. Conductor Types RHH, RHW, RHW-2, THHN,
THHW, THW, THW-2, THWN, THWN-2, XHHW,
XHHW-2, SE, USE, USE-2

 

[iwire]

Look at the first words in the section you mentioned.

(7) 120/240-Volt, Single-Phase Dwelling Services and Feeders. For one-family dwellings and the individual dwe11ing units of two-family and multifamily dwellings, service and feeder conductors supplied by a single-phase, 120/240-volt system shall be permitted be sized in accor-dance with 310.15(B)(7)(l) through (4).

So that is out of the question for 208 volt services and feeders.

As far as 338.10(B)(4) the PE is correct if you run SE in insulated walls etc.

( 4) Installation Methods for Branch Circuits and Feeders.

(a) Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Pmt II of Article 334, excluding 334.80. Where installed in thermal insulation the ampacity shall be in accordance with the 60?C (140?F) conductor temperature rating. The maximum conductor temperature rating shall be pel1l1itted to be used for ampacity adjustment and correction purposes, if the final derated ampacity does not exceed that for a 60?C (140?F) rated conductor.

Do you know the calculated load for each unit?

 

[jhall]

Does 310.15(B)(7) apply to 120/208v 1ph dwellings and does it supersede 338.10(B)(4)?

On what theory basis would you reject the that 120/208v services would not be applicable to 310.15B7? The largest dwelling loads, (i.e. Range, Dryer, and electric heat or heat pump) pulls LESS amps at 208volts than 240v. Which I am sure would be the case for all other resistive loads. Therefore the "actual" demand/load would be LESS at 208v than 240v. If the table applies to 240v, it makes zero since that it would not also apply to 208v.
Respectfully. Thank you in advance for your reply.

 

[Dennis Alwon]

On what theory basis would you reject the that 120/208v services would not be applicable to 310.15B7? The largest dwelling loads, (i.e. Range, Dryer, and electric heat or heat pump) pulls LESS amps at 208volts than 240v. Which I am sure would be the case for all other resistive loads. Therefore the "actual" demand/load would be LESS at 208v than 240v. If the table applies to 240v, it makes zero since that it would not also apply to 208v.
Respectfully. Thank you in advance for your reply.

The table heading states 120/240 3 wire single phase dwelling services and feeders.

 

[jhall]

Does 310.15(B)(7) apply to 120/208v 1ph dwellings and does it supersede 338.10(B)(4)?

To answer your previous question about load. The calculated loads for smallest units is 120.6amps the largest is 129.8. All calculations were done using optional, 1st 10kva at 100% remainder at 40%. The PE used 208v in his calcs, but used 240v ratings on all the resistive heat loads. Just FYI.

 

[Dennis Alwon]

[h=2]Does 310.15(B)(7) apply to 120/208v 1ph dwellings and does it supersede 338.10(B)(4)?[/h]

No it does not apply as I mentioned above. In the 2014 the table is removed and we are to use 83%. Thus all ampacity adjustments must be considered. In the 2011 it was not stated that way but apparently that is what they wanted.

 

[iwire]

To answer your previous question about load. The calculated loads for smallest units is 120.6amps the largest is 129.8. All calculations were done using optional, 1st 10kva at 100% remainder at 40%. The PE used 208v in his calcs, but used 240v ratings on all the resistive heat loads. Just FYI.

So going with 130 amps and using 240.4(B) you could use 3/0 AL.