3, 30A circuits through 1 conduit

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jhp

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Hi.

I'm looking to run 3, 30A circuits (9 conductors) through 1 conduit. I will be using 3 Junction boxes to house the receptacles.

I have 2 questions.

1. How far apart do the junction boxes need to be from each other? Is there a code for this?

2. If i run 10AWG wires rated for 105 deg C with OD of 0.18" through a 1/2" IMC, would this be fine according to the NEC? How about 8AWG with 105 deg C with OD of 0.262" through a 3/4" IMC?

According to the NEC, running 9 conductors through a conduit means that I have to lower the current rating to 70% of the table. If I want 30A circuits, that means that I have to look for a 43A value on the table for the wire size I want to use. According to the table, I can use cables rating at 90 deg C for 40A for a 10AWG. Guess my question is, can I just get higher rated wires to make up that extra 3A?

Thanks,
-Jeff
 
jhp said:
Hi.

I'm looking to run 3, 30A circuits (9 conductors) through 1 conduit. I will be using 3 Junction boxes to house the receptacles.

I have 2 questions.

1. How far apart do the junction boxes need to be from each other? Is there a code for this?

2. If i run 10AWG wires rated for 105 deg C with OD of 0.18" through a 1/2" IMC, would this be fine according to the NEC? How about 8AWG with 105 deg C with OD of 0.262" through a 3/4" IMC?

According to the NEC, running 9 conductors through a conduit means that I have to lower the current rating to 70% of the table. If I want 30A circuits, that means that I have to look for a 43A value on the table for the wire size I want to use. According to the table, I can use cables rating at 90 deg C for 40A for a 10AWG. Guess my question is, can I just get higher rated wires to make up that extra 3A?

Thanks,
-Jeff
Click to expand...

Welcome to the forum.
There will be no code restriction on the box spacing, just normal mechanical considerations, namely whether or not the covers will easily work.

For your wire fill, have you found how to calculate these? The conduits you're proposing are both too small for wires with those diameters. What wire types are you planning to use? Do they need to be 105 degrees? Maybe you should look at them again, and we can find a thinner insulation that will work.
 
jhp said:
Hi.

I'm looking to run 3, 30A circuits (9 conductors) through 1 conduit. I will be using 3 Junction boxes to house the receptacles.

I have 2 questions.

1. How far apart do the junction boxes need to be from each other? Is there a code for this?
Click to expand...
No Code restriction
jhp said:
2. If i run 10AWG wires rated for 105 deg C with OD of 0.18" through a 1/2" IMC, would this be fine according to the NEC? How about 8AWG with 105 deg C with OD of 0.262" through a 3/4" IMC?
Click to expand...
Unsure what type wire you are using but the OD is real close to XHHW (#10= .0176) and the Code allows 9#10 XHHW thru a 3/4 EMT so you are probably close, but a 1" might be better

jhp said:
According to the NEC, running 9 conductors through a conduit means that I have to lower the current rating to 70% of the table. If I want 30A circuits, that means that I have to look for a 43A value on the table for the wire size I want to use. According to the table, I can use cables rating at 90 deg C for 40A for a 10AWG. Guess my question is, can I just get higher rated wires to make up that extra 3A?

Thanks,
-Jeff
Click to expand...
You are allowed to derate on the insulation ampacity. Your 105? does not correspond to standard US ratings, but a #10 THHN is 90? C and has an amapcity of 28 amps when derated for 9 CCC (70%).

In summary, my OPINION is that you might need a 1" conduit until you have less than 9 conductors although 3/4 might just be within Code, and your #10 should be o.k. on a 30 amp load.
 
augie47 said:
In summary, my OPINION is that you might need a 1" conduit until you have less than 9 conductors although 3/4 might just be within Code, and your #10 should be o.k. on a 30 amp load.
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I disagree with this statement that I highlighted in red because of what he says here.

jhp said:
I'm looking to run 3, 30A circuits (9 conductors) through 1 conduit. I will be using 3 Junction boxes to house the receptacles.
Click to expand...

NEC 2008 240.4(B)(1) will not allow him to go to the next higher ocd above the ampacity of the conductors. #10 was derated to 28 amps. He has to down size to at least 25 amps or use bigger wire (assuming this is the #10 THHN 90degree C United States standard) . ;)
 
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brother said:
I disagree with this statement that I highlighted in red because of what he says here.



NEC 2008 240.4(B)(1) will not allow him to go to the next higher ocd above the ampacity of the conductors. #10 was derated to 28 amps. He has to down size to at least 25 amps or use bigger wire (assuming this is the #10 THHN 90degree C United States standard) . ;)
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\

Are you saying that a single receptacle with an adjusted ampacity of 28 amps cannot on a 30 amp OCPD?
 
The 30 amp devices are ok on the 28 amp wire 210.21(B)(1). The load can't exceed the 28 amp rating.

Whether or not it is a good idea is a design concern for that particular installation.
 
brother said:
I disagree with this statement that I highlighted in red because of what he says here.



NEC 2008 240.4(B)(1) will not allow him to go to the next higher ocd above the ampacity of the conductors. #10 was derated to 28 amps. He has to down size to at least 25 amps or use bigger wire (assuming this is the #10 THHN 90degree C United States standard) . ;)
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I made that same argument in a long running thread earlier and was convinced I was in error.
From the OP it appeard these circuits were not feeding a multi-outlet branch circuit which is what 240.4(B) addresses.
 
infinity said:
\

Are you saying that a single receptacle with an adjusted ampacity of 28 amps cannot on a 30 amp OCPD?
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No I am not. Im saying exactly what the NEC says,

240.4(B)(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptalces for cord and plug connected portable loads.

So if it is a single receptalce, then its not a multioutlet. It just appeared from his posts that he had more than one receptacle attached to those conductors. Maybe th o.p. can clarify
 
brother said:
No I am not. Im saying exactly what the NEC says,

240.4(B)(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptalces for cord and plug connected portable loads.

So if it is a single receptalce, then its not a multioutlet. It just appeared from his posts that he had more than one receptacle attached to those conductors. Maybe th o.p. can clarify
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You could be right. I took it as 3-single 30 amp, 3 phase receptacles. Since he's talking about 9 CCC's I'm assuming 3 phase which led me to believe that each circuit would have a single receptacle.
 
infinity said:
You could be right. I took it as 3-single 30 amp, 3 phase receptacles. Since he's talking about 9 CCC's I'm assuming 3 phase which led me to believe that each circuit would have a single receptacle.
Click to expand...

After reading the o.p. first post again, I do believe your right.

jhp said:
I'm looking to run 3, 30A circuits (9 conductors) through 1 conduit. I will be using 3 Junction boxes to house the receptacles
Click to expand...
 
Nium said:
I'm kinda wondering why you have 9 conductors for 3 circuits. Are these 3 phase or multiwire branch circuits?
Click to expand...

Another suggestion?

(3) 30A, 240v, single phase circuits with a neutral load....as in (3) 30A electric clothes dryers.

He didn't say anything about 9 current carrying conductors....just maybe he is assuming he has to count all 9 conductors...common error for those not real familiar with the specifics of derating.

....if this is the case, then he really only has 6 CCCs...problem solved.

Unfortunately the OP has not given us the additional info we need to give a real accurate answer to his inquiry.
 
I think we need more info on the loads supplied by these three circuits before we can help much more. Is 30 amps the actual load, is it adjusted for continuous load if necessary, is it motors, air conditioning, heating, other?
 
let me jump in

let me jump in

Many years ago as a greenhorn>>>>>>> I gave my old timer a hard time about exact calculations/deratings/pipefill etc..... " ' LOOK SON' no more than 6 hots in a pipe, #12's in 1/2 pipe or # 10 in 3/4 pipe and so on >>> single phase or 3phase, Do not stretch it unless ya have to". I wish the Codebook could say it that easily!!!!!!!!!
 
dana1028 said:
Another suggestion?

(3) 30A, 240v, single phase circuits with a neutral load....as in (3) 30A electric clothes dryers.

He didn't say anything about 9 current carrying conductors....just maybe he is assuming he has to count all 9 conductors...common error for those not real familiar with the specifics of derating.

....if this is the case, then he really only has 6 CCCs...problem solved.
Unfortunately the OP has not given us the additional info we need to give a real accurate answer to his inquiry.
Click to expand...

He did say that the derating was at 70% which would be indicative of more than 6 CCC's. But you could be right, until we hear all of the details we're all just guessing. :)

rt66electric said:
Many years ago as a greenhorn>>>>>>> I gave my old timer a hard time about exact calculations/deratings/pipefill etc..... " ' LOOK SON' no more than 6 hots in a pipe, #12's in 1/2 pipe or # 10 in 3/4 pipe and so on >>> single phase or 3phase, Do not stretch it unless ya have to". I wish the Codebook could say it that easily!!!!!!!!!
Click to expand...

I can be that easy if you just want to use a rule of thumb and not figure out the actual number of CCC's. :grin:
 
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