Circuits In 3/4"emt | Mike Holt's Forum

Menu

• Home
• Forums New posts Search forums
• What's new New posts

Log in Register What's new Search

Search

Everywhere Threads This forum This thread Search titles only By: Search Advanced search…

• New posts
• Search forums

Menu Log in Register

• Home
• Forums
• Active Forums
• Electrical Calculations / Engineering

You are using an out of date browser. It may not display this or other websites correctly.You should upgrade or use an alternative browser. circuits in 3/4"emt

• Thread starter ginnia
• Start date Oct 26, 2010

Status Not open for further replies.

• 1
• 2

Next 1 of 2

Go to page

Go Next Last G

ginnia

New member

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

480sparky

Senior Member

Location Iowegia Your answer will depend on the ampacity needed. If you only need 15 amps, you can get 16 total conductors.

jwjrw

Senior Member

480sparky said: Your answer will depend on the ampacity needed. If you only need 15 amps, you can get 20 CCCs. Click to expand...

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

Moderator

Staff member Location New Jersey Occupation Journeyman Electrician (retired) 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

infinity said: 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. Click to expand...

Which table should I be using? OOPS I quoted #14 sorry!

infinity

Moderator

Staff member Location New Jersey Occupation Journeyman Electrician (retired)

jwjrw said: Which table should I be using? OOPS I quoted #14 sorry! Click to expand...

Right table, wrong conductor size. :grin:

jwjrw

Senior Member

infinity said: Right table, wrong conductor size. :grin: Click to expand...

Yea when I saw you posted 16 I had to go look again. 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? Last edited: Oct 26, 2010

480sparky

Senior Member

Location Iowegia

jwjrw said: Yea when I saw you posted 16 I had to go look again. 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? Click to expand...

Yep .

kwired

Electron manager

Location NE Nebraska Occupation EC

ginnia said: 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 Click to expand...

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

Moderator

Staff member Location New Jersey Occupation Journeyman Electrician (retired)

kwired said: 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. Click to expand...

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

iwire

Moderator

Staff member Location Massachusetts

kwired said: 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. Click to expand...

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

kwired said: 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. Click to expand...

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

kwired

Electron manager

Location NE Nebraska Occupation EC

infinity said: The size limitation of 310.4(A) does not apply to EGC's. Click to expand...

iwire said: 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. Click to expand...

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.

kwired

Electron manager

Location NE Nebraska Occupation EC

480sparky said: May be so in the real world, but I suspect the OP is posting a test question. Click to expand...

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

480sparky

Senior Member

Location Iowegia

kwired said: part of the answer to the question is that only one EGC is needed whether the person writing the question realizes it or not. Click to expand...

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 Last edited: Oct 28, 2010 S

stevenje

Senior Member

Location Yachats Oregon

480sparky said: 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 Click to expand...

I assume you meant 30 feet and not 30 inches. B

Barndog

Senior Member

Location Spring Creek Pa

480sparky said: 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 Click to expand...

My answer would be C.

LarryFine

Master Electrician Electric Contractor Richmond VA

Location Henrico County, VA Occupation Electrical Contractor

stevenje said: I assume you meant 30 feet and not 30 inches. Click to expand...

Depends on whether they're talking about vertical or horizontal distance. B

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.

infinity

Moderator

Staff member Location New Jersey Occupation Journeyman Electrician (retired)

kwired said: 310.4(E) only allows EGC's smaller than 1/0 to be paralleled if part of a multiconductor cable. Click to expand...

Where does it say that EGC's in the same or multiple raceways cannot be connected on both ends?

• 1
• 2

Next 1 of 2

Go to page

Go Next Last Status Not open for further replies. Share: Facebook X (Twitter) Reddit Pinterest Tumblr WhatsApp Email Share Link

• Home
• Forums
• Active Forums
• Electrical Calculations / Engineering

Top