parallel conduits different sizes

[dickfitzgerald1960@gmail.]

Existing 200A 120/240v 1-phase residential meter-main w/ a 2" pvc feeder. Service to be upgraded to 400A w/ addtl. parallel pvc conduit. Is there any reason why new conduit cannot be bigger than 2"?

Dick Fitzgerald

 

[infinity]

So you want to create parallel conductors with one raceway being larger than the other?

310.10(H)(3) Separate Cables or Raceways. Where run in separate cables or raceways, the cables or raceways with conductors shall
have the same number of conductors and shall have the same electrical characteristics. Conductors of one phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor shall not be required to have the same physical characteristics as those of another phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor

Welcome to the Forum.

 

[dickfitzgerald1960@gmail.]

One pvc conduit larger than the existing other if that doesn't violate "same electrical characteristics."

 

[LarryFine]

PVC would not affect impedance characteristics, so ought need not match, as long as the conductors still do.

 

[infinity]

If both raceways are made from PVC IMO the electrical characteristics are the same.

 

[qcroanoke]

If size of raceway is a characteristic then you can't do that. Although I can't see where it could possibly matter

 

[Coppersmith]

Just make sure the wire is the same type, size, and length.

Also, if this second conduit is terminating in a second (separate) panel, then you aren't creating parallel runs and none of the above advice applies.

 

[norcal]

You should check PoCo specs to see what they allow/want, if I am reading this correctly.

 

[winnie]

If size of raceway is a characteristic then you can't do that. Although I can't see where it could possibly matter

If the raceway is metallic, and especially if it is ferromagnetic, then the characteristics of the raceway will measurably alter the electrical characteristics of the conductors. In such a case the size of the raceway would clearly matter.

With non metallic raceway, I don't think there would be any significant difference in conductor characteristics.

Jon

 

[paulengr]

If the raceway is metallic, and especially if it is ferromagnetic, then the characteristics of the raceway will measurably alter the electrical characteristics of the conductors. In such a case the size of the raceway would clearly matter.

With non metallic raceway, I don't think there would be any significant difference in conductor characteristics.

Jon

I agree in theory but is it significant? I mean there’s not much difference going to 2.5”. By the time you go to 3-3.5” you might as well just take advantage of the fact that now you can use the 90 C rating but derating for more than 3 conductors works out to virtually the same. We check this all the time in the motor business. So with 1-3 conductors using say THWN-2 it’s 90 C rated wet or dry in the conduit but at the terminals it’s nearly always 75 C rated so we use the lower ampacity limit or 75 C. With two conductors per phase in the same conduit again we take the 90 C column but then derate to 80% which just happens to be the same as the 75 C column. So if you are wanting to increase the conduit size anyway check how much bigger you need to go for fill reasons with the increased conductors. You will find in most cases this is easier. Plus you don’t have to match conductor sizes, types, lengths, etc. Wire is cheap. Conduit is cheap and you’re already paying the labor to pull it.