Derating

[Capacitorx]

How many #12 thhns can u have in a 3/4 inch emt current carrying conductor wise?i thought because the actual ampacity capacity of a number 12 thhn was 30 amp but not to have over-current protection above 20,but u could still.factor in the 30 for derating purposes so u could use the 70% ADJUSTMENT FACTOR and still fit 9 in.

 

[charlie b]

You have that right. I find it interesting that some people remember the "limit of 9," but don't know where it comes from, and are unaware that it only works for #12 wire. For #10 wire and 30 amp circuits, the corresponding limit is 6.

 

[jumper]

You have that right. I find it interesting that some people remember the "limit of 9," but don't know where it comes from, and are unaware that it only works for #12 wire. For #10 wire and 30 amp circuits, the corresponding limit is 6.

Works for #14 also.

 

[infinity]

For #10 wire and 30 amp circuits, the corresponding limit is 6.

What about 9 CCC's and the next size up rule?

40 amps * 70% = 28 amps, next size up 30 amps.

 

[Dennis Alwon]

What about 9 CCC's and the next size up rule?

40 amps * 70% = 28 amps, next size up 30 amps.

That is assuming the load is 28 amps or less, of course.

 

[don_resqcapt19]

That is assuming the load is 28 amps or less, of course.

And assuming you are not serving multioutlet receptacle circuits.

 

[infinity]

And assuming you are not serving multioutlet receptacle circuits.

Yes, but that seems somewhat unlikely on 30 amp circuits.

 

[Capacitorx]

Derating

I had a discussin with my coworkers one believes that the only way you can get 4.single phase 20 amp circuits into a 3/4 emt was to upsize to 10 wire.they argued that uyou cannot derate using the 30 amp max capacity because the max overcurrent breaker rating your allowed to us is 20 amp.And that because your only supposed to use 80 % of the load on the actual value of the breaker and max capacity of said conductor.he said max allowed in 3/4 emt is 7 for #12 and 9 for #10.so on another note am I rite in thinking I could use adjustment factor 50% for single phase 20 amp circuits by derating to #10 awg thhn based on that #10s max amp capacity is 40 amps so 50% would be 20 amps which is still within the breakers rating,so in a larger pipe I could use 10 to 20 # current carrying conductors as long as I didnt go over 40 percent of the conduit's internal diameter.am I correct in thinking this if anyone could clear this up abit I would be much appreciated

 

[Twoskinsoneman]

I had a discussin with my coworkers one believes that the only way you can get 4.single phase 20 amp circuits into a 3/4 emt was to upsize to 10 wire.they argued that uyou cannot derate using the 30 amp max capacity because the max overcurrent breaker rating your allowed to us is 20 amp.

Kindly point them to 110.14(C)

 

[infinity]

I had a discussin with my coworkers one believes that the only way you can get 4.single phase 20 amp circuits into a 3/4 emt was to upsize to 10 wire.they argued that uyou cannot derate using the 30 amp max capacity because the max overcurrent breaker rating your allowed to us is 20 amp.And that because your only supposed to use 80 % of the load on the actual value of the breaker and max capacity of said conductor.he said max allowed in 3/4 emt is 7 for #12 and 9 for #10.so on another note am I rite in thinking I could use adjustment factor 50% for single phase 20 amp circuits by derating to #10 awg thhn based on that #10s max amp capacity is 40 amps so 50% would be 20 amps which is still within the breakers rating,so in a larger pipe I could use 10 to 20 # current carrying conductors as long as I didnt go over 40 percent of the conduit's internal diameter.am I correct in thinking this if anyone could clear this up abit I would be much appreciated

You're correct except for the part about 80% of the OCPD size. You can use up to 100% as long as it's not a continuos load.