Neutral Conductor Sizing & 310.15(B)(7)

[George Stolz]

I didn't say the neutral could not be smaller. I am saying that it's ampacity must match the neutral load. 310.15(B)(6) is not an ampacity table. Compare table 310.15(B)(6) with table 310.16. What differences do you see?

 

[jumper]

I didn't say the neutral could not be smaller. I am saying that it's ampacity must match the neutral load. 310.15(B)(6) is not an ampacity table. Compare table 310.15(B)(6) with table 310.16. What differences do you see?

The ampacity of the ungrounded conductors does not match in the two tables either.

 

[George Stolz]

The key I see are the titles of the tables, differences in figures aside.

 

[jumper]

The key I see are the titles of the tables, differences in figures aside.

Where does it say this only applies to ungrounded conductors?

(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services
and Feeders. For individual dwelling units of one family,
two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(6), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance conductors,
service-lateral conductors, and feeder conductors

Table 310.15(B)(6) 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

This applies, but it does not say I cannot use T310.15(B)(6) to size the neutral here.

The grounded conductor shall be permitted to be
smaller than the ungrounded conductors, provided the requirements
of 215.2, 220.61, and 230.42 are met.

 

[Smart $]

Where does it say this only applies to ungrounded conductors?

It does not. But the conductor sizes permitted under the Table are based on the service rating, not the minimum required ampacity (i.e. calculated load).

This applies, but it does not say I cannot use T310.15(B)(6) to size the neutral here.

The grounded conductor shall be permitted to be
smaller than the ungrounded conductors, provided the requirements
of 215.2, 220.61, and 230.42 are met.

In order to go smaller than the Table allows, you have to meet the cited requirements, period. Nowhere does it say any single conductor can be sized smaller than given per the service or feeder rating because its calculated load is less than said rating.