circuits in 3/4"emt

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ginnia

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How many circuits usin #12 thhn in emt 3/4". I have to use 75c b/c term blocks are speced . I came up with 4 cir. (we have to use seperate n AND seperate not isolated grounds) Using uglys book i came up with 7to 9 current carr. cond tbl I ythen used corr factors to come up with 15.4 a is it ok to use 4 cir? thanks jj
 

jwjrw

Senior Member
Your answer will depend on the ampacity needed. If you only need 15 amps, you can get 20 CCCs.


3/4 emt will hold 22 thhn wires according to table c1. Are you saying after he adjusts ampacity he could still get 20 ccc?
 

infinity

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3/4" EMT can only have 16-#12 THHN conductors for 40% fill.

How many CCC's do you have?

You can use the 90? C rating for THHN for derating.
 

jwjrw

Senior Member
Right table, wrong conductor size. :grin:


Yea when I saw you posted 16 I had to go look again. :D

Ok say you has 9 CCC.

310.16 says THHN #12 is good for 30 amps 90 deg. So 30a x .70 = 21 amps. Correct?
 
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kwired

Electron manager
Location
NE Nebraska
How many circuits usin #12 thhn in emt 3/4". I have to use 75c b/c term blocks are speced . I came up with 4 cir. (we have to use seperate n AND seperate not isolated grounds) Using uglys book i came up with 7to 9 current carr. cond tbl I ythen used corr factors to come up with 15.4 a is it ok to use 4 cir? thanks jj

there is no point in separate grounding conductors in a raceway except for isolated grounds

Read 250.148 they will all need to be tied together in every outlet or junction box effectively making them one - which also would be a violation of 310.4(A) because they would be in parallel and you can't parallel conductors smaller than 1/0 AWG.
 

infinity

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there is no point in separate grounding conductors in a raceway except for isolated grounds

Read 250.148 they will all need to be tied together in every outlet or junction box effectively making them one - which also would be a violation of 310.4(A) because they would be in parallel and you can't parallel conductors smaller than 1/0 AWG.

The size limitation of 310.4(A) does not apply to EGC's.
 

iwire

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Location
Massachusetts
Read 250.148 they will all need to be tied together in every outlet or junction box effectively making them one - which also would be a violation of 310.4(A) because they would be in parallel and you can't parallel conductors smaller than 1/0 AWG.

I agree with Rob, 310.4 does not apply to EGCs and that is good because EGCs are almost always in parallel in some way.
 

480sparky

Senior Member
Location
Iowegia
there is no point in separate grounding conductors in a raceway except for isolated grounds

Read 250.148 they will all need to be tied together in every outlet or junction box effectively making them one - which also would be a violation of 310.4(A) because they would be in parallel and you can't parallel conductors smaller than 1/0 AWG.

May be so in the real world, but I suspect the OP is posting a test question.
 

kwired

Electron manager
Location
NE Nebraska
The size limitation of 310.4(A) does not apply to EGC's.

I agree with Rob, 310.4 does not apply to EGCs and that is good because EGCs are almost always in parallel in some way.

310.4(E) only allows EGC's smaller than 1/0 to be paralleled if part of a multiconductor cable. A good example of this is a switch or outlet box with more than one circuit supplied by NM cables. The grounds if (and they should) be all tied together would put the EGC from the two or more cables from the supply in parallel with each other.
 

480sparky

Senior Member
Location
Iowegia
part of the answer to the question is that only one EGC is needed whether the person writing the question realizes it or not.


Still, when it comes to test questions, you answer it as a test question, not a real-life situation.

My favorite test question is:

How many #10 THHN stranded conductors can be pulled into a 1" PVC conduit run 30" underground between two buildings?

A. 10
B. 12
C. 15
D. 17
 
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stevenje

Senior Member
Location
Yachats Oregon
Still, when it comes to test questions, you answer it as a test question, not a real-life situation.

My favorite test question is:

How many #10 THHN stranded conductors can be pulled into a 1" PVC conduit run 30" underground between two buildings?

A. 10
B. 12
C. 15
D. 17

I assume you meant 30 feet and not 30 inches. ;)
 

Barndog

Senior Member
Location
Spring Creek Pa
Still, when it comes to test questions, you answer it as a test question, not a real-life situation.

My favorite test question is:

How many #10 THHN stranded conductors can be pulled into a 1" PVC conduit run 30" underground between two buildings?

A. 10
B. 12
C. 15
D. 17

My answer would be C.
 

billyzee

Member
5 Circuits

5 Circuits

Table C.1 says 3/4" EMT is good for 16 THHN

If you need individual ground for each circuit then you need three wires for each circuit. This means 5 circuits maximum.

5 circuits means 10 current carrying conductors. Therefore Table 310.15(B)(2)(a) limits you to 50% of the ampacity.

The 90 deg column ampacity in Table 310.16(A) is OK to use for derating just so long as the result is not greater than the 75 deg column. Therefore each of you circuits is limited to .5 x 30A = 15 amps.

This means you shouldn't be using 20 amp breakers. Even using 15 amp breakers may cause persnickity inspectors to cause problems because you arn't supposed to allow continuous current greater than 80% of breaker trip setting.
 
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