MWBC Romex capacity at 208/120 (3W 1ph) vs 120/240 home power

[Flicker Index]

While all three conductors are considered current carrying conductors, they don't add up the same way.

If you put a 120v 1200w light bulb on each pole, you'll have 10A on each line. In 120/240, the neutral will carry zero or negligible amount of current.
In 208/120 3W 1ph, all three conductors will carry 10A, thus 1.5 x the I^2R loss within the same jacket.

Does this have to be taken into consideration?

 

[CoolWill]

Yes, you have to count the neutral as a current carrying conductor for derating purposes when two of the three phase conductors are used. Not so for 120/240 V.

 

[retirede]

The way you’re describing your scenario, you will have 3 bulbs in the 3 phase case, so the load is 1.5 times. So losses are proportionally equivalent.

 

[wwhitney]

The way you’re describing your scenario, you will have 3 bulbs in the 3 phase case, so the load is 1.5 times. So losses are proportionally equivalent.

The title should say 120/208 rather than the 208/120, but the parenthetical comment clarifies that it is 3W 1ph. So there are only two bulbs, and the losses are proportionally more (3 CCCs @ 10A rather than 2) than on 120/240. Add a 3rd bulb on a 208Y/120, and your comment applies.

Cheers, Wayne

 

[retirede]

The title should say 120/208 rather than the 208/120, but the parenthetical comment clarifies that it is 3W 1ph. So there are only two bulbs, and the losses are proportionally more than on 120/240. Add a 3rd bulb on a 208Y/120, and your comment applies.

Cheers, Wayne

Missed that! Thanks.