Wires in an EMT Conduit

[ABEN]

Hi all, I am relatively new to electrical estimation and I need some answers from the more experienced people (estimating for Commercial Public Work projects):

1) How many #12 current-carrying conductors are practically acceptable in a 1" EMT (for home runs)? Some online conduit fill calculators show (26) #12 to be just 40% fill ratio but then there's a question about heat dissipation.

2) Are the numbers the same for residential projects? If not what is practically allowed in those scenarios?

 

[Dennis Alwon]

If you keep the runs to 2' or less then there is not an issue with heat. The tables are good for both residential and commercial. Remember the type of insulation is also a factor when using the tables.

Also 60% fill is allowed. Chapter 9 Note 4

 

[ABEN]

Thanks for the reply, Dennis. My runs are somewhere between 60-80'. The type is THHN rated for 600V. What should I consider in that case?

 

[Dennis Alwon]

Well you will have to derate to 50% if you put 12 conductors in there. I wouldn't do what you are doing but if I did I would probably run 3 full boats-- that is 3 neutrals and 9 current carrying conductor's-- in that case the neutrals wouldn't be considered current carrying conductor's so the de-rating would be 70%

Table 310.15(B)(3)9a)

 

[infinity]

To use the 20 amp rating of #12 THHN you need to keep the CCC's below 10.

 

[tom baker]

And just a note EMT is not conduit. Picky, maybe, but if you had bid a job where the specs called for conduit, and you bid EMT, you lost money on that bid.

 

[Ponchik]

Are the loads continuous?

 

[ABEN]

Well you will have to derate to 50% if you put 12 conductors in there. I wouldn't do what you are doing but if I did I would probably run 3 full boats-- that is 3 neutrals and 9 current carrying conductor's-- in that case the neutrals wouldn't be considered current carrying conductor's so the de-rating would be 70%

Table 310.15(B)(3)9a)

Got it, thank you

 

[ABEN]

And just a note EMT is not conduit. Picky, maybe, but if you had bid a job where the specs called for conduit, and you bid EMT, you lost money on that bid.

Well, it actually calls for EMT, but thanks for pointing out.

 

[kwired]

To use the 20 amp rating of #12 THHN you need to keep the CCC's below 10.

yes.

If supplying multiple general receptacle outlets, you sort of have to assume you can load them to 20 amps.

If you have fixed loads you only need to consider actual connected load when adjusting conductor ampacity.

 

[acin]

Well you will have to derate to 50% if you put 12 conductors in there. I wouldn't do what you are doing but if I did I would probably run 3 full boats-- that is 3 neutrals and 9 current carrying conductor's-- in that case the neutrals wouldn't be considered current carrying conductor's so the de-rating would be 70%

Table 310.15(B)(3)9a)

Is that table from 2017 ? 310 .15 (b) (3) (a)

 

[acin]

Got it Dennis , shift key pren .