tpapke@kmtel.net
Member
Code location for maximum conductors in a 1" RMC run??? confused tpapke@kmtel.net
maximum conductors in conduit
- Thread starter tpapke@kmtel.net
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
Re: maximum conductors in conduit
See 344.22 which sends you to Chapter 9, Table 1. These are the actual code rules for the number of conductors in a raceway, but there are tables in Annex C for installations where all of the conductors are of the same size. Table C8 is for rigid metal conduit. If all of the conductors are not the same size you will have to make some calculations based on the information in Chapter 9, Tables 1, 4 and 5.
Don't forget that if there are more than 3 current carrying conductors, you will have to derate the ampacity of the conductors per 310.15(B)(2).
Don
See 344.22 which sends you to Chapter 9, Table 1. These are the actual code rules for the number of conductors in a raceway, but there are tables in Annex C for installations where all of the conductors are of the same size. Table C8 is for rigid metal conduit. If all of the conductors are not the same size you will have to make some calculations based on the information in Chapter 9, Tables 1, 4 and 5.
Don't forget that if there are more than 3 current carrying conductors, you will have to derate the ampacity of the conductors per 310.15(B)(2).
Don
tpapke@kmtel.net
Member
Re: maximum conductors in conduit
Just to clarify I am setting up a truck line and need 20 independant outlets on a leg wifh means I need 10 #12 thhn energized wires 10 #12 thhn neutrals and 1 #6 ground..... is this even close
Just to clarify I am setting up a truck line and need 20 independant outlets on a leg wifh means I need 10 #12 thhn energized wires 10 #12 thhn neutrals and 1 #6 ground..... is this even close
tpapke@kmtel.net
Member
Re: maximum conductors in conduit
Just to clarify I am setting up a truck line and need 20 independant outlets on a leg wifh means I need 10 #12 thhn energized wires 10 #12 thhn neutrals and 1 #6 ground..... is this even close herdelec@kmtel.net help
I am plugging in 20 trucks for block heaters. I have room for 1" conduit. I am outside. I need individual breakers for each truck.
[ June 08, 2003, 05:51 PM: Message edited by: tpapke@kmtel.net ]
Just to clarify I am setting up a truck line and need 20 independant outlets on a leg wifh means I need 10 #12 thhn energized wires 10 #12 thhn neutrals and 1 #6 ground..... is this even close herdelec@kmtel.net help
I am plugging in 20 trucks for block heaters. I have room for 1" conduit. I am outside. I need individual breakers for each truck.
[ June 08, 2003, 05:51 PM: Message edited by: tpapke@kmtel.net ]
jtb
Senior Member
- Location
- Pennsylvania
Re: maximum conductors in conduit
"20 independent" to me would mean 20 "hots", 20 Neutrals, and ground(s). I am not sure what a truck line is...I am assuming you need 20 receptacles with 20A available to each?
"20 independent" to me would mean 20 "hots", 20 Neutrals, and ground(s). I am not sure what a truck line is...I am assuming you need 20 receptacles with 20A available to each?
Re: maximum conductors in conduit
Seems to me that this would be an " outside " location. If so, be sure the conductor type has a " W " in it such as THWN.
tpake mentions, " on a leg ".
Seems as though a multiwire system could be used unless the Spec's don't allow.
Multiwire system would reduce the conduit fill on either a 3W or a 4W system. If not, you will have 40 Current Carring Conductors ( CCC ) 40 percent derate and if outside, may have to apply a temperature correction also.
Most likely, you will need to be careful that the " Derating " does not take the Ampacity of the conductor to below 15 Amps on receptacle of 15 Amp rating and not below 20 Amps if the receptcales are 20 Amp rating. 210.21(B)(1).
[ June 08, 2003, 04:08 PM: Message edited by: gwz2 ]
Seems to me that this would be an " outside " location. If so, be sure the conductor type has a " W " in it such as THWN.
tpake mentions, " on a leg ".
Seems as though a multiwire system could be used unless the Spec's don't allow.
Multiwire system would reduce the conduit fill on either a 3W or a 4W system. If not, you will have 40 Current Carring Conductors ( CCC ) 40 percent derate and if outside, may have to apply a temperature correction also.
Most likely, you will need to be careful that the " Derating " does not take the Ampacity of the conductor to below 15 Amps on receptacle of 15 Amp rating and not below 20 Amps if the receptcales are 20 Amp rating. 210.21(B)(1).
[ June 08, 2003, 04:08 PM: Message edited by: gwz2 ]
pierre
Senior Member
- Location
- Westchester County, New York
Re: maximum conductors in conduit
It is very difficult to give the proper answer without the proper input, next time review your post first and then you will see these guys give you an answer you can use.
Pierre
It is very difficult to give the proper answer without the proper input, next time review your post first and then you will see these guys give you an answer you can use.
Pierre
tvgaconsultants
Member
Re: maximum conductors in conduit
tpapke,
I understand what yo are looking for. You have twenty trucks that have block heaters in them( ie. diesels). Don gave you the right information. The only thing I see that I question is the #6 ground? If a 120V 20A circuit only requires a #12 ground. The calcs Don gave can get confusing if need more assistance send email to me and I will try to assist.
tpapke,
I understand what yo are looking for. You have twenty trucks that have block heaters in them( ie. diesels). Don gave you the right information. The only thing I see that I question is the #6 ground? If a 120V 20A circuit only requires a #12 ground. The calcs Don gave can get confusing if need more assistance send email to me and I will try to assist.
Re: maximum conductors in conduit
No matter how you look at it, you can't get all this in a 1" conduit and meet your parameters. First off, the conduit fill on a 1" is only 29 #12's. You need 20 dedicated circuits. This would require 20 #12's for the load conductors. You did not say they need to be isolated, so you could run a 4-wire "round-house". But then you'd need to pull a #10 nuetral with each round-house. This would be a total of 7 #10's and a #10 ground. This calculates out to .3812 sq. in. of fill. A 1" conduit has a capacity of .34 sq. in. fill. So it won't fit. Plus, you'd have to derate the load capacity to 60% or 12 amps total per dedicated circuit.
The proper installation would require #10's and a larger conduit, or more than 1 conduit run to feed this number of dedicated circuits.
[ July 05, 2003, 03:18 AM: Message edited by: frogg ]
No matter how you look at it, you can't get all this in a 1" conduit and meet your parameters. First off, the conduit fill on a 1" is only 29 #12's. You need 20 dedicated circuits. This would require 20 #12's for the load conductors. You did not say they need to be isolated, so you could run a 4-wire "round-house". But then you'd need to pull a #10 nuetral with each round-house. This would be a total of 7 #10's and a #10 ground. This calculates out to .3812 sq. in. of fill. A 1" conduit has a capacity of .34 sq. in. fill. So it won't fit. Plus, you'd have to derate the load capacity to 60% or 12 amps total per dedicated circuit.
The proper installation would require #10's and a larger conduit, or more than 1 conduit run to feed this number of dedicated circuits.
[ July 05, 2003, 03:18 AM: Message edited by: frogg ]
- Location
- Massachusetts
Re: maximum conductors in conduit
I am curious why you would need to run a larger neutral than the ungrounded conductors?
I do agree he does not have enough conduit space to do this job.
Bob
By "round-house" I assume (oh no) that you mean a multiwire branch circuit.
I am curious why you would need to run a larger neutral than the ungrounded conductors?
I do agree he does not have enough conduit space to do this job.
Bob
Re: maximum conductors in conduit
(oh no) Bob, I guess I should never have used any field terminolgy, just in case some new electricians are reading any of this. I suppose we should stick to strict code language. Sorry.
But yes, I don't know where or even if for a fact that it is a NEC requirement, I thought that it was a new code. We have installed 4 recent large jobs that the cities required and the local inspectors required the upsize of the nuetral when pulled in a multi conductor branch circuit. This was required by the electrical engineer in the approved drawings, and we have been checked on it by local inspectors when it wasn't called for in the drawings. When just two phases are in the multi conductor circuit, the load is not extremely unbalanced, whereas when there are three phases, the load can be extremely unbalanced, possibly more ampacity than the #12 nuetral is rated at... thus the #10.
I don't recall when I first ran into this, but I too questioned it and was told that the third wire created the unbalanced load that is a culprit in problems related to computer voltage spikes and harmonics.
Could all be a huge multi-person misunderstanding. I surely would like to know if they are right, because it is truly a pain in the arse to pull the 10 with the 12's.
Another requirement is the sizing of conduit ond fill on these larger comm/Ind installations. 1 multi conductor in a half inch, 2 in a three quarter inch, and 3 in a 1 inch.
Anybody else hear of the upsizing of the nuetral? I know we get called on it here in sunny southern California.
Frogg
(oh no) Bob, I guess I should never have used any field terminolgy, just in case some new electricians are reading any of this. I suppose we should stick to strict code language. Sorry.
But yes, I don't know where or even if for a fact that it is a NEC requirement, I thought that it was a new code. We have installed 4 recent large jobs that the cities required and the local inspectors required the upsize of the nuetral when pulled in a multi conductor branch circuit. This was required by the electrical engineer in the approved drawings, and we have been checked on it by local inspectors when it wasn't called for in the drawings. When just two phases are in the multi conductor circuit, the load is not extremely unbalanced, whereas when there are three phases, the load can be extremely unbalanced, possibly more ampacity than the #12 nuetral is rated at... thus the #10.
I don't recall when I first ran into this, but I too questioned it and was told that the third wire created the unbalanced load that is a culprit in problems related to computer voltage spikes and harmonics.
Could all be a huge multi-person misunderstanding. I surely would like to know if they are right, because it is truly a pain in the arse to pull the 10 with the 12's.
Another requirement is the sizing of conduit ond fill on these larger comm/Ind installations. 1 multi conductor in a half inch, 2 in a three quarter inch, and 3 in a 1 inch.
Anybody else hear of the upsizing of the nuetral? I know we get called on it here in sunny southern California.
Frogg
- Location
- Illinois
- Occupation
- retired electrician
Re: maximum conductors in conduit
The only reason to make the neutral of a 3 phase 4 wire multiwire branch circuit larger than the pahse conductors is if the load is mostly nonlinear. If the load is balanced and linear the current on the neutral of a 3 phase multiwire branch circuit will be 0.
don
The only reason to make the neutral of a 3 phase 4 wire multiwire branch circuit larger than the pahse conductors is if the load is mostly nonlinear. If the load is balanced and linear the current on the neutral of a 3 phase multiwire branch circuit will be 0.
don
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