Daisy Chained Receptacles in Conduit - 310.15(A) ?

[TwoBlocked]

Pretty sure I got this right, but would like some verification.

A wall in a typical industrial site needs receptacles every so many feet with all raceways being rigid conduit. A horizontal conduit with tees is run up near the ceiling. At each tee a conduit is run to a few feet from the floor where they end in receptacle outlets. The conductors are daisy chained from one receptacle to the next with 4 current carrying conductors in the vertical conduits and 2 current carrying conductors in the horizontal conduits. Lets say 10 receptacles on a 20 amps breaker with #12 THHN wire.

Paragraph 2 of 310.15(A) states "The temperature and correction and adjustment factors shall be permitted to be applied to the ampacity for the temperature rating of the conductor, if the corrected and adjusted ampacity does not exceed the ampacity for the temperature rating of the termination in accordance with the provisions of 110.14(C)."

So we look at Table 310.15(C)(1) and get an adjustment factor of 80%. Applying this to #12 THHN , 90deg column of Table 310.16 we get 24 amps (30 x .80 = 24). This does not exceed the ampacity shown in the 75deg column (25A), Also it is greater than the maximum sized OCPD for #12 wire (20A) as per 240.4(D). I find the same thing with conductors #18 thru #10. They can be daisy chained without lowering the max ampacity of the OCPD.

Bottom line is you can run up to 6 current carrying THHN conductors #18-#10 in a raceway without downsizing the OCPD.

Right or wrong, or is there more?

 

[LarryFine]

You're correct.

 

[infinity]

With #12 THHN you can put up to 9 CCC's in a raceway before the adjustment drops you below 20 amps.

 

[don_resqcapt19]

Pretty sure I got this right, but would like some verification.

A wall in a typical industrial site needs receptacles every so many feet with all raceways being rigid conduit. A horizontal conduit with tees is run up near the ceiling. At each tee a conduit is run to a few feet from the floor where they end in receptacle outlets. The conductors are daisy chained from one receptacle to the next with 4 current carrying conductors in the vertical conduits and 2 current carrying conductors in the horizontal conduits. Lets say 10 receptacles on a 20 amps breaker with #12 THHN wire.

Paragraph 2 of 310.15(A) states "The temperature and correction and adjustment factors shall be permitted to be applied to the ampacity for the temperature rating of the conductor, if the corrected and adjusted ampacity does not exceed the ampacity for the temperature rating of the termination in accordance with the provisions of 110.14(C)."

So we look at Table 310.15(C)(1) and get an adjustment factor of 80%. Applying this to #12 THHN , 90deg column of Table 310.16 we get 24 amps (30 x .80 = 24). This does not exceed the ampacity shown in the 75deg column (25A), Also it is greater than the maximum sized OCPD for #12 wire (20A) as per 240.4(D). I find the same thing with conductors #18 thru #10. They can be daisy chained without lowering the max ampacity of the OCPD.

Bottom line is you can run up to 6 current carrying THHN conductors #18-#10 in a raceway without downsizing the OCPD.

Right or wrong, or is there more?

With 15, 20 and 30 amp breakers, you can use 14, 12, and 10AWG respectively as long as there are no more than 9 current carrying conductors in the raceway.

 

[Little Bill]

With #12 THHN you can put up to 9 CCC's in a raceway before the adjustment drops you below 20 amps.

Beat me to it!

 

[jap]

If the T's were large enough I'd splice in the T's and save wire and reduce the heat.

JAP>

 

[TwoBlocked]

If the T's were large enough I'd splice in the T's and save wire and reduce the heat.

JAP>

You'd have to go pretty big, at least 1-1/4"

 

[TwoBlocked]

With 15, 20 and 30 amp breakers, you can use 14, 12, and 10AWG respectively as long as there are no more than 9 current carrying conductors in the raceway.

Hadn't realized all this, but you are limited to 6 conductors if there are receptacle loads with #10. Can't upsize the OCPD - 240.4(B)(1)

 

[infinity]

Hadn't realized all this, but you are limited to 6 conductors if there are receptacle loads with #10. Can't upsize the OCPD - 240.4(B)(1)

True, but one everyday practice what size 30 amp receptacle loads use duplex receptacles or more than one single on a circuit?

 

[TwoBlocked]

True, but one everyday practice what size 30 amp receptacle loads use duplex receptacles or more than one single on a circuit?

Ya got a point!

 

[TwoBlocked]

If the T's were large enough I'd splice in the T's and save wire and reduce the heat.

JAP>

You'd have to go pretty big, at least 1-1/4"

Looks like you'd have to go to a 2" tee. A box would be better, but there's an advantage to having your connections where you can get to them easily.

 

[jap]

Looks like you'd have to go to a 2" tee. A box would be better, but there's an advantage to having your connections where you can get to them easily.

We could always use the rigid as the EGC and only have to splice 3 #12 hots and 3 #12 neutrals in each T.

JAP>

 

[TwoBlocked]

We could always use the rigid as the EGC and only have to splice 3 #12 hots and 3 #12 neutrals in each T.

JAP>

Guess you could. Something I don't usually do. Lot of broken conduit in manufacturing plants. Third shift fork truck drivers. Can't say I'd do any better.

 

[infinity]

Why would you want to use an oversized T conduit body and splice in it when you can just pull the wires in and out to each receptacle?

 

[electrofelon]

I've always hated tees and can't think of a reason to use them most of the time.

 

[TwoBlocked]

I've always hated tees and can't think of a reason to use them most of the time.

When the storeroom stocks tees and boxes, and covers for the tees, but not the boxes. Yeah, starting new job on Monday.

 

[infinity]

When the storeroom stocks tees and boxes, and covers for the tees, but not the boxes. Yeah, starting new job on Monday.

There are advantages an disadvantegs to both methods. Boxes require support conduit bodies do not so that's one advantage to not using a box. Since you're already splicing at the receptacles why add more splices at the "T" points. You might save some wire with the boxes but will have more labor.

 

[don_resqcapt19]

Hadn't realized all this, but you are limited to 6 conductors if there are receptacle loads with #10. Can't upsize the OCPD - 240.4(B)(1)

Yes with receptacle loads you can't protect the 28 amp conductor with a 30 amp OCPD.

 

[don_resqcapt19]

I've always hated tees and can't think of a reason to use them most of the time.

In my industrial work, I probably used twice as many tees as I did any other conduit body.

 

[infinity]

Yes with receptacle loads you can't protect the 28 amp conductor with a 30 amp OCPD.

Don, what about with only a single receptacle on a circuit