actual numbers of current carrying conductors in conduit

[sparky00004]

in the code book under emt conduit fill for #12 thhn,thwn it is allowed 16 number 12,but it also says that more than three current carrying conductors in raceway or cable,you must derate and apply adjustment factors so 4-6=80% 7-9=70% 10-20=50%
it also says that a 12thwn at 75 degrees terminatin under a 75 degree terminal is capable of handling up to 25 amps ans 12thhn at 90degrees can handle up to 30 amps,but most terminations are under 75 degrees terminals
so that tells me that if i had six number 12 in 3/4 emt conduit thhn,thwn conductors i will derate at a value of 25 amps*80%=20 amps.

so i want to new if six number 12 thhn,thwn in a 3/4 emt conduit is the most wires allowed before i would have to go to the next size wire.

 

[George Stolz]

It's always a max of 9 CCCs when dealing with EMT and THHN, since you begin derating from the 90? column.

 

[480sparky]

It's always a max of 9 CCCs when dealing with EMT and THHN, since you begin derating from the 90? column.

Nine is the magic number for me as well. You derate according to the column in T310.16 (Art. 310.15 tells you this), not according to the terminal temp. limit of 110.14(C).

Oh, and welcome to the forum!

 

[iwire]

It's always a max of 9 CCCs when dealing with EMT and THHN, since you begin derating from the 90? column.

Nine is the magic number for me as well.

To clarify, 9 is the number when dealing with 10, 12 and 14 AWG 90 C conductors.

Once you get into 8 AWG and larger things change and you may have issues with 4 or more.

 

[infinity]

in the code book under emt conduit fill for #12 thhn,thwn it is allowed 16 number 12,but it also says that more than three current carrying conductors in raceway or cable,you must derate and apply adjustment factors so 4-6=80% 7-9=70% 10-20=50%
it also says that a 12thwn at 75 degrees terminatin under a 75 degree terminal is capable of handling up to 25 amps ans 12thhn at 90degrees can handle up to 30 amps,but most terminations are under 75 degrees terminals
so that tells me that if i had six number 12 in 3/4 emt conduit thhn,thwn conductors i will derate at a value of 25 amps*80%=20 amps.

so i want to new if six number 12 thhn,thwn in a 3/4 emt conduit is the most wires allowed before i would have to go to the next size wire.

For THHN you would use the 90 degree ampacity for derating. THWN you would use the 75 degree ampacity for derating. So for #12 conductors THHN would give you up to 9 CCC's before needing to increase the condcutor size. For THWN that would become 6 CCC's before increasing condcutor size.

THHN-30 amps * 70% = 21 amps
THWN-25 amps * 80% = 20 amps

 

[TOOL_5150]

For THHN you would use the 90 degree ampacity for derating. THWN you would use the 75 degree ampacity for derating. So for #12 conductors THHN would give you up to 9 CCC's before needing to increase the condcutor size. For THWN that would become 6 CCC's before increasing condcutor size.

THHN-30 amps * 70% = 21 amps
THWN-25 amps * 80% = 20 amps

All the spools from southwire I get are dual rated. FWIW

~Matt

 

[tkb]

It depends on how you use the wire.
In dry locations you can use is as THHN and in wet locations, like underground as THWN.

 

[Smart $]

To clarify, 9 is the number when dealing with 10, 12 and 14 AWG 90 C conductors.

Once you get into 8 AWG and larger things change and you may have issues with 4 or more.

To make it a bit more clear, 9 ccc's is the magic number if using the maximum permitted rating for the ocpd under the small conductor rules of 240.4(D), i.e.

#14@15A
#12@20A
#10@30A​

An alternative to upsizing the wire is to downsize the ocpd, but this depends heavily on the load served.

However, I often wonder about #14 on a 15A-ocpd-protected circuit... the way the code is currently worded. If we were to run 10-20 #14 thhn ccc's derated to 50% of their 90?C 25A rating, would not the adjusted ampacity of 12.5A (or lower if derated for ambient temperature) permit the next larger standard ocpd of 15A???

 

[hillbilly]

To make it a bit more clear, 9 ccc's is the magic number if using the maximum permitted rating for the ocpd under the small conductor rules of 240.4(D), i.e.

#14@15A
#12@20A
#10@30A​

An alternative to upsizing the wire is to downsize the ocpd, but this depends heavily on the load served.

However, I often wonder about #14 on a 15A-ocpd-protected circuit... the way the code is currently worded. If we were to run 10-20 #14 thhn ccc's derated to 50% of their 90?C 25A rating, would not the adjusted ampacity of 12.5A (or lower if derated for ambient temperature) permit the next larger standard ocpd of 15A???

Sounds right to me.
Although, you would be limited to 12.5 amps load on the conductor.

steve

 

[iwire]

would not the adjusted ampacity of 12.5A (or lower if derated for ambient temperature) permit the next larger standard ocpd of 15A???

Sure if it is not supplying a mutli receptacle circuit and the load is still under the derated conductor amapcity.

 

[iwire]

It depends on how you use the wire.
In dry locations you can use is as THHN and in wet locations, like underground as THWN.

Most wire is now "-2" which means 90C wet or dry.

 

[infinity]

Most wire is now "-2" which means 90C wet or dry.

That's true. I was only responding to the question in the OP which said:

12 in 3/4 emt conduit thhn,thwn conductors

 

[George Stolz]

Er, uh, yeah! That's my excuse too!

 

[tkb]

Most wire is now "-2" which means 90C wet or dry.

I forgot about that.

 

[charlie b]

To clarify, 9 is the number when dealing with 10, 12 and 14 AWG 90 C conductors.

I would agree for 12 and 14, but not for 10.

With 9 ccc's, and #10 THHN wire, you get 70% of 40, or 28 amps. You can protect that with a 30 amp breaker, but you cannot use it for a calculated load (i.e., accounting for both continuous and non-continuous) of 30 amps. So my rule of thumb is that the magic number for #10 wire is 6 ccc's.

 

[Smart $]

I would agree for 12 and 14, but not for 10.

With 9 ccc's, and #10 THHN wire, you get 70% of 40, or 28 amps. You can protect that with a 30 amp breaker, but you cannot use it for a calculated load (i.e., accounting for both continuous and non-continuous) of 30 amps. So my rule of thumb is that the magic number for #10 wire is 6 ccc's.

Good point!!!

 

[pierrewoody]

conduit fill

conduit fill

Hello,

So, for any size PVC, the ccc's is always 9? What about the number of conductors, could I run 8 hot, 4 neutral all no 14 THHN without derating? I need 8-15A circuits.