Multiple Conductors in a Raceway

[viclibo]

Hi All,
I am running 20 #12 circuits in emt, outside, residential, THHN, 45 feet. I have the calc's. Wanna compare notes? Thanks in advance.

 

[cadpoint]

Run the numbers... give us a pitch!

Show the Tail of the Tape...

 

[bob]

You first.

 

[viclibo]

40 current carrying conductors = 40 % ampacity therefore to obtain 20 amp you need a #8. 40 # 8's =2.5 inch emt ( 64 allowed in 2.5 but only 36 in a 2 inch) #8 THHN at 90 degrees is 50 amp @40% =20 amp.

 

[viclibo]

I would run all #8's, 20 hot, 20 neutral and one ground.

 

[LarryFine]

Run a feeder to a sub-panel.


Can these be made into MWBC's?

 

[viclibo]

Thanks Larry........................that is soooooooooooo true and a good lesson learned. A feeder to a sub panel is the way to go.

 

[480sparky]

Thanks Larry........................that is soooooooooooo true and a good lesson learned. A feeder to a sub panel is the way to go.

Larry Fine, ladies and gentlemen! Give 'im a big hand!

He's here all week, and twice on Saturday!
Don't forget to tip your waitress!

 

[JES2727]

Hi All,
I am running 20 #12 circuits in emt, outside, residential, THHN, 45 feet. I have the calc's. Wanna compare notes? Thanks in advance.

40 current carrying conductors = 40 % ampacity therefore to obtain 20 amp you need a #8. 40 # 8's =2.5 inch emt ( 64 allowed in 2.5 but only 36 in a 2 inch) #8 THHN at 90 degrees is 50 amp @40% =20 amp.

If you're running "20 #12 circuits", that calculates to 20 twelve amp circuits. Why are you running #8 for "#12 circuits"? #8 is overkill for a 12 amp load....:grin:

 

[infinity]

Pulling 41-#8's in a 2.5" raceway is a poor design. You should run more than one conduit and use smaller conductors or do what Larry suggested.

 

[viclibo]

Table 310.15 (B)(2)(a) if using 31-40 current carrying conductors in a raceway you have to de rate the conductor. Table 310-16 # 12 is rated at 30 amp and @40 % it goes to 12 amp. # 8 is rated at 55 amp and @ 40% goes to 22 amp. I would never do this but got called on a similar situation recently so this is fresh.

 

[480sparky]

....... Why are you running #8 for "#12 circuits"? #8 is overkill for a 12 amp load....:grin:

Table 310.15(B)(2)(a).

 

[JES2727]

Table 310.15 (B)(2)(a) if using 31-40 current carrying conductors in a raceway you have to de rate the conductor. Table 310-16 # 12 is rated at 30 amp and @40 % it goes to 12 amp. # 8 is rated at 55 amp and @ 40% goes to 22 amp. I would never do this but got called on a similar situation recently so this is fresh.

Of course. I understand that. But you already established in your first post that you plan to install "#12 circuits". Of course you meant "20 amp circuits", I was just pouncing on your wording just to mess things up.

 

[Jim W in Tampa]

Go for it. Please make vidio to share. I want to watch this pull. Seriously ,run more conduits or do as Larry suggested.