# Parelleled service conductor question



## EmmettEnterprise (Dec 29, 2016)

Hey all, installing a single phase 400a service for a farm. Pretty straightforward installation. Going to be paralleling 4/0 conductors to keep the cost down obviously. My question is, am I required to run each conductor set in its own conduit or can I run both sets in a single run of conduit? 

In past 400a installations we've just run all paralleled conductors in the same conduit, but I've been hearing talk that each conductor set is required to be run in its own conduit, I just can't find the code to back that up. 

Thanks in advance- Trevor.


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## 360max (Jun 10, 2011)

its.ok,derating-applies


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## EmmettEnterprise (Dec 29, 2016)

Derating as in?


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## 360max (Jun 10, 2011)

See section 310.15B2a of NEC


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## 360max (Jun 10, 2011)

Derating is an adjustment factor when three or more current carrying conductors are installed in raceway or cable


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## Dennis Alwon (May 9, 2009)

What size conductors are you using?


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## EmmettEnterprise (Dec 29, 2016)

4/0 urd


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## frenchelectrican (Mar 15, 2007)

What is the distance is??

I think the 4/0 urd may squeak by but I doubt it.


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## EmmettEnterprise (Dec 29, 2016)

Roughly 120'


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## EmmettEnterprise (Dec 29, 2016)

So I'm using 4/0 USE-2 which per table 310.15-b-16 has an ampacity of 205a.

My ambient temp should be in the 60-68 bracket of table 310-.15-b-2-b which would give me a multiplier of 1.18. Which puts my ampacity at 242a.

I would have more than 3 current carrying conductors in the conduit so according to table 310.15-b-3-a I can only have 80% of that 242a which leaves me with 194amps. 

So if my calcs are correct I need to put my conductors in two separate runs of conduit to avoid having to up the size of my conductors?


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## telsa (May 22, 2015)

EmmettEnterprise said:


> Hey all, installing a single phase 400a service for a farm. Pretty straightforward installation. Going to be paralleling 4/0 conductors to keep the cost down obviously. My question is, am I required to run each conductor set in its own conduit or can I run both sets in a single run of conduit?
> 
> In past 400a installations we've just run all paralleled conductors in the same conduit, but I've been hearing talk that each conductor set is required to be run in its own conduit, I just can't find the code to back that up.
> 
> Thanks in advance- Trevor.


Most common boner in parallel feeders: under-sized grounding (bonding) conductor.

It must be sized for the full 400A.

The hots and neutral can be sized for 200A.

On an economic basis -- shun copper -- go with aluminum -- up-size the raceway -- so that you can run 350 kCMIL. ( XHHW-2 in AL ) 

[ It's a super popular wire gauge. ]

Price it out.


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## hardworkingstiff (Jan 22, 2007)

EmmettEnterprise said:


> 4/0 urd


Is that aluminum?


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## EmmettEnterprise (Dec 29, 2016)

I'm thinking my solution to this problem will be to run two separate conduits and avoid having to derate the conductors, and plan for larger conductors in the future. Does anyone see a fault with that?


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## Roger123 (Sep 23, 2007)

I'll assume this is an underground install since you are running URD. 

If that is the case why use conduit at all, except when you come out of the ground and then right into the socket.


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## Dennis Alwon (May 9, 2009)

EmmettEnterprise said:


> I'm thinking my solution to this problem will be to run two separate conduits and avoid having to derate the conductors, and plan for larger conductors in the future. Does anyone see a fault with that?


Two separate conduits are not required but perhaps it will be easier. The trick is to get all conductors of a phase to be exactly the same length


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## Dennis Alwon (May 9, 2009)

EmmettEnterprise said:


> So I'm using 4/0 USE-2 which per table 310.15-b-16 has an ampacity of 205a.
> 
> My ambient temp should be in the 60-68 bracket of table 310-.15-b-2-b which would give me a multiplier of 1.18. Which puts my ampacity at 242a.
> 
> ...



Actually you will still be limited to 180 amps per run however if your connected load is 360 amps or less then you can use an overcurrent protective device of 400 amps. 

Your ampacity is limited to the terminals which are rated 75C not 90C.

Either upsize to a 250 MCM or keep the load at 360 amps or less


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## Forge Boyz (Nov 7, 2014)

Roger123 said:


> I'll assume this is an underground install since you are running URD.
> 
> If that is the case why use conduit at all, except when you come out of the ground and then right into the socket.


If you ever need to replace the cable you will be glad for the conduit. None of the POCO's we work with use direct bury anymore and I for sure wouldn't. 

Sent from my XT1585 using Tapatalk


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## Southeast Power (Jan 18, 2009)

Dennis Alwon said:


> Two separate conduits are not required but perhaps it will be easier. The trick is to get all conductors of a phase to be exactly the same length


Describe "exactly"


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## 360max (Jun 10, 2011)

Dennis Alwon said:


> Two separate conduits are not required but perhaps it will be easier. The trick is to get *all conductors of a phase to be exactly the same length*


:whistling2:


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## Roger123 (Sep 23, 2007)

Forge Boyz said:


> If you ever need to replace the cable you will be glad for the conduit. None of the POCO's we work with use direct bury anymore and I for sure wouldn't.
> 
> Sent from my XT1585 using Tapatalk


My point was if URD is used it doesn't need conduit. If conduit is used URD is the hardest to pull.

Also, First Engery/Ohio Edison is a big poco company in Ohio/Penn and I believe NJ. Where I work, NE Ohio they routinely direct bury cable in residential.


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## djp879 (Jul 22, 2016)

Dennis Alwon said:


> Two separate conduits are not required but perhaps it will be easier. The trick is to get all conductors of a phase to be exactly the same length




Conduits are required to take the same path...it's impossible to get the "same length" but the runs should be parallel the whole run so your lengths are similar.


Sent from my iPhone using Tapatalk


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## Dennis Alwon (May 9, 2009)

Suncoast Power said:


> Describe "exactly"





360max said:


> :whistling2:


Not sure what the issue is.. When you parallel conductors they must be the same length



> Conductor and Installation Characteristics. The paralleled
> conductors *in each phase,* polarity, neutral, grounded
> circuit conductor, equipment grounding conductor, or equipment
> bonding jumper shall comply with all of the following:
> ...


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## Dennis Alwon (May 9, 2009)

djp879 said:


> Conduits are required to take the same path...it's impossible to get the "same length" but the runs should be parallel the whole run so your lengths are similar.
> 
> 
> Sent from my iPhone using Tapatalk


It is not impossible and is required as noted above. You measure it out ahead of time for the longest run and you have to leave a loop or do something to make up the difference.

The code does not say the lengths should be similar-- what does that mean-- 1', 2' ???


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## sbrn33 (Mar 15, 2007)

Forge Boyz said:


> If you ever need to replace the cable you will be glad for the conduit. None of the POCO's we work with use direct bury anymore and I for sure wouldn't.
> 
> Sent from my XT1585 using Tapatalk


I would run conduit also but in real life it is waaay easier to repair a direct bury line that was damaged than a conduit run.


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## Dennis Alwon (May 9, 2009)

sbrn33 said:


> I would run conduit also but in real life it is waaay easier to repair a direct bury line that was damaged than a conduit run.


Yes, that's true but it is easier for a direct burial cable to go bad. All it takes is a small nic and the aluminum conductor will degrade rapidly. I have seen it many time.

My friend was running a 600' run to a solar array. I told him to run a conduit but instead he ran some extra conductors. Good thing because within a year he had trouble with one conductor. I wonder how long before another issue. In some areas, rocks are an issue and it's hard to pick thru them all.


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## 360max (Jun 10, 2011)

Dennis Alwon said:


> Suncoast Power said:
> 
> 
> > Describe "exactly"
> ...


I fully understand what the code says, ' same length', my problem is the practicality , tough to enforce rule


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## djp879 (Jul 22, 2016)

360max said:


> I fully understand what the code says, ' same length', my problem is the practicality , tough to enforce rule




I've done hundreds of these...as long as your conduits are taking the same path, they're not going to say something like, this one is 6 inches shorter....lol. They look for the parallel and you fulfill the code the best way possible. Just order your feeders the same length and you'll be fine...i don't know why people make this more difficult than it should be.


Sent from my iPhone using Tapatalk


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## don_resqcapt19 (Jul 18, 2010)

Dennis Alwon said:


> It is not impossible and is required as noted above. You measure it out ahead of time for the longest run and you have to leave a loop or do something to make up the difference.
> 
> The code does not say the lengths should be similar-- what does that mean-- 1', 2' ???


It is impossible to get them the same length unless you accept some amount of tolerance. The code does not specify a permitted tolerance, but it should.


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## sbrn33 (Mar 15, 2007)

don_resqcapt19 said:


> It is impossible to get them the same length unless you accept some amount of tolerance. The code does not specify a permitted tolerance, but it should.


Please no more codes. It is waay out of hand the way it is.


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## don_resqcapt19 (Jul 18, 2010)

sbrn33 said:


> Please no more codes. It is waay out of hand the way it is.


Based on the current code wording for parallel conductors, the inspector could red tag all parallel installations as it really is impossible to make the conductors the same length. 

The code needs to specify a percentage tolerance that is acceptable for the length of parallel conductors.


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## sbrn33 (Mar 15, 2007)

don_resqcapt19 said:


> Based on the current code wording for parallel conductors, the inspector could red tag all parallel installations as it really is impossible to make the conductors the same length.
> 
> The code needs to specify a percentage tolerance that is acceptable for the length of parallel conductors.


How would you prove either one?


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## splatz (May 23, 2015)

don_resqcapt19 said:


> It is impossible to get them the same length unless you accept some amount of tolerance. The code does not specify a permitted tolerance, but it should.


I agree as far as you can't have a rule without making it specific, a vague rule is just an argument looking for a place to happen. Along with a tolerance, I'd say it's necessary to say what's an acceptable method to measure the length. If you are trying to be "exact" it's pretty hard to precisely measure the length of a cable. 

But then if you're going to be a geek about it, why get precise about the length, that's not really what matters, isn't the idea to get the current more or less even on the conductors? If that's the case the length wouldn't be the thing to obsess over, the resistance would be.


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## hardworkingstiff (Jan 22, 2007)

splatz said:


> If that's the case the length wouldn't be the thing to obsess over, the resistance would be.


Since the conductors are to be the same type and terminated the same way, the resistance of the overall conductor is determined by its length.

I've always considered a % of difference as the critical measurement. 

If you have 10' of parallel conductors compared to 100' of parallel conductors, a 1' difference in 10' would have the same effect on current divide as 10' in the 100' run.


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## splatz (May 23, 2015)

hardworkingstiff said:


> Since the conductors are to be the same type and terminated the same way, the resistance of the overall conductor is determined by its length.


Theoretically, in a perfect world, with perfect cable. In reality, I don't think that's true, especially on longer cables. 

I have also noticed when playing with a TDR that wires you think are the same length don't always come up the same. I am not sure whether it's the actual length, or variations in the wire's velocity of propagation, or both. Or just which one gets cranked harder / bent more during installation.


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## Dennis Alwon (May 9, 2009)

don_resqcapt19 said:


> It is impossible to get them the same length unless you accept some amount of tolerance. The code does not specify a permitted tolerance, but it should.


If you are talking exactly to the quarter inch I would agree but you can get them damn close by laying them out together. 

Sure the inspectors have no way to know but you don't want to overload one conductor so they need to be very close. The further the run the less of an issue it will be, IMO.


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## MechanicalDVR (Dec 29, 2007)

If you are talking conductors side by side in a conduit, it would be impossible to measure them so it's kind of an odd point to raise on behalf of an inspector.


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## B-Nabs (Jun 4, 2014)

So if you've got a 300' run you're going to lay out two conductors side by side to make sure they're identical in length? That sounds unreasonable to me, and in some cases impossible. I just make sure my conduits follow the same path, order my cables cut and go for the gusto.

I had someone show me a method once where they used the cut off piece from the first cable of a phase to measure how much to cut off of the second. Problem I see with that is that often the cables you get from the supplier are not exactly the same length anyway.

I agree that a tolerance should be specified, but then as others have said that raises the question of how do you confirm an installation is within the tolerance? I would say a cable length measuring device, or testing for millivolt drop or some such thing.

I don't know, as time goes on I tend to worry a little less about it.


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## MechanicalDVR (Dec 29, 2007)

B-Nabs said:


> So if you've got a 300' run you're going to lay out two conductors side by side to make sure they're identical in length? That sounds unreasonable to me, and in some cases impossible. I just make sure my conduits follow the same path, order my cables cut and go for the gusto.
> 
> I had someone show me a method once where they used the cut off piece from the first cable of a phase to measure how much to cut off of the second. *Problem I see with that is that often the cables you get from the supplier are not exactly the same length anyway.*
> 
> ...



You hit that nail on the head.


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## don_resqcapt19 (Jul 18, 2010)

Dennis Alwon said:


> If you are talking exactly to the quarter inch I would agree but you can get them damn close by laying them out together.
> 
> Sure the inspectors have no way to know but you don't want to overload one conductor so they need to be very close. The further the run the less of an issue it will be, IMO.


But my point is that the code says the same length and does not give any tolerance. You are correct that the longer the run the less an issue it is, and that is why I suggested a percentage.

You can get close to the current division by using the lengths as the resistance and solving the total parallel resistance, and then working out the current based on the individual "resistances".


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## telsa (May 22, 2015)

Parallel conduits suffice.

I've heard tell of retro-fits where the old work was PVC underground -- the new work was EMT -- above ground.

This combo was Red Tagged.

The old PVC run had to be re-pulled and a coil of 33' left, serpentine, to mate up with the EMT run. 

This was the only way to get the conductors 'right.'

Power propagates at the speed of light in copper// aluminum. So keeping them within a foot or two of each other gets the job done. 

Be aware that looping coils of your conductor triggers an RL circuit -- an 'air-core' transformer -- after a fashion. Work to entirely avoid them.

[ See also: voltage surge suppressors. You don't want sharp bends in their conductors, either. ]

Every time you 'turn' an AC wave form you increase its impedance. Normally, this is so trivial that we can safely neglect it. But things 'get strange' when the pulse of power is extreme. ( lightning// coil collapse)


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