# Number of conductors in a conduit



## backstay (Feb 3, 2011)

Count them as conduit fill? Or as current carrying?

1.MWBC (not what you have)
2. Two hots one neutral (not what you have)
3. You didn’t give us enough information to determine that.


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## kb1jb1 (Nov 11, 2017)

Linear or non linear loads? If it is for resistive loads or incandescent lighting type stuff then no but if it is for non Linear loads then yes. NEC 315.B.5 I think.


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## VELOCI3 (Aug 15, 2019)

Wire type?
Terminal temp rating?
Conduit location?
Highest temperature of area where conduit will be ran?


Sent from my iPad using Tapatalk


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## craigdj87 (Oct 11, 2016)

backstay said:


> Count them as conduit fill? Or as current carrying?
> 
> 1.MWBC (not what you have)
> 2. Two hots one neutral (not what you have)
> 3. You didn’t give us enough information to determine that.


I would like to not count the Neutrals as current carrying.
This is for a dental office with patient care rooms.
Led lighting.


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## backstay (Feb 3, 2011)

craigdj87 said:


> I would like to not count the Neutrals as current carrying.
> This is for a dental office with patient care rooms.
> Led lighting.



(3)
On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral conductor shall therefore be considered a current-carrying conductor.





Does #3 fit your job? If so, you have to count them.


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## craigdj87 (Oct 11, 2016)

Well, there will be computers, monitors, motorized dental chairs, Xray equipment and led lighting. So, I guess those are all Non-Linear


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## kb1jb1 (Nov 11, 2017)

Dedicated neutrals otherwise you have to use three pole breakers. If one circuit goes down for whatever reason then the other two will also go down. Don't forget the redundant grounding.


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## HertzHound (Jan 22, 2019)

craigdj87 said:


> Well, there will be computers, monitors, motorized dental chairs, Xray equipment and led lighting. So, I guess those are all Non-Linear


Other than the X-ray equipment, I doubt any of the other items contribute to any harmonic current that would make the neutral “current carrying”. Maybe someone that does power quality type work can chime in on the harmonic current boogie man. 

The x-ray equipment may have special requirements that you have to look into. Sometimes they ask for an equipment ground that is the same size as the phase conductors, or some other odd requirements. In your case, if it’s only a 20a circuit, the ground thing probably isn’t a problem, because the ground is already a #12. It may even say they want a dedicated neutral?

That being said, if I was in your situation, I would pull separate neutrals. Not because I believe you have high harmonic currents, but because I don’t like sharing neutrals anymore. Years ago I would have felt defeated if I had a circuit that couldn’t be combined with another and needed a separate neutral. After years of job specs that require separate neutrals, no handle ties, and NEC changes, etc., I gave up. Everything gets a separate neutral anymore. If you really wanted to go for it, share the neutrals on everything except the x-ray equipment.


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## Flekota (Mar 18, 2017)

craigdj87 said:


> I would like to not count the Neutrals as current carrying.
> This is for a dental office with patient care rooms.
> Led lighting.


Doesn't matter its considered current carrying conductor anymore there is no such thing as a neutral. Its current carrying at ground potential. Alway really has been that, but it has caused many death. but It can heat up just like the primary (hot) legs you have to have space to dispense heat if there is a wire there it can heat up and if there is no air space heat does not dispense


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## splatz (May 23, 2015)

I'd probably rather just run two 3/4" for this, do the x-ray per the manufacturer's instructions, no shared neutral, and put the rest in the other conduit with shared neutrals. I think harmonics are like bigfoot, often talked about but seldom seen.


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## kb1jb1 (Nov 11, 2017)

Anothering thing about sharing neutral. Has anybody opened up a junction box to trace out wires only to have a wire nut pop off and the previous electrician did not pre-twist the wires? I have and it was the white wire that seperated. Guess what happened next?


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## backstay (Feb 3, 2011)

kb1jb1 said:


> Anothering thing about sharing neutral. Has anybody opened up a junction box to trace out wires only to have a wire nut pop off and the previous electrician did not pre-twist the wires? I have and it was the white wire that seperated. Guess what happened next?


🔥


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## Southeast Power (Jan 18, 2009)

craigdj87 said:


> I'm not understanding 310.15 E.
> I want to run 9 hots on 3 3pole breakers with 3 Neutrals in a 3/4-inch EMT. Derating at 70% which brings me down to 21 amps. So, I'm good there. Do I count the Neutrals or not?
> 
> Thanks


I would do it if I had no other choice or if the cost was too prohibitive or too disruptive. 
FWIW, I'm in the camp of pulling a #10 neutral with that type of circuit. The most imbalance you can have is going to depend on the loads. The X-ray equipment could be an issue but, typically an X-ray is about 4 seconds in duration with very short pulses. If you have complete control of the lighting and receptacle loads, you can manage the lighting, and any phase to phase loads. 
Just keep in mind you do have to consider the next electrician that comes along might not have the education you have.
With all of that said, 
I will have to agree with Splatz and go with 2x homeruns.


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## West Coast Sparky (Nov 14, 2021)

I'm in suspense here... what happened next?


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## Almost Retired (Sep 14, 2021)

splatz said:


> I'd probably rather just run two 3/4" for this, do the x-ray per the manufacturer's instructions, no shared neutral, and put the rest in the other conduit with shared neutrals. I think harmonics are like bigfoot, often talked about but seldom seen.


i agree with seldom seen

but i look for it to become more common, southwire already makes 12-2G with a #10 neutral
there are electronic power supplies and such that will put them out, and that will raise the current on the neutral
usually not, but sometimes over the rating

im wondering if the time has come where new construction should be wiring for it to allow future loads


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## crwilliams (Oct 26, 2012)

I’m surprised that in a patient care environment there is no mention of GFCI. That of course won’t work with shared neutrals so I would suggest separate neutrals if only for future proofing. Also at 15 wires, assuming #12, you are right up against the simplistic 16 wire fill maximum. I would suggest going up to 1 in or using two runs, as others have suggested.


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## Almost Retired (Sep 14, 2021)

edit


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## just the cowboy (Sep 4, 2013)

kb1jb1 said:


> Anothering thing about sharing neutral. Has anybody opened up a junction box to trace out wires only to have a wire nut pop off and the previous electrician did not pre-twist the wires? I have and it was the white wire that seperated. Guess what happened next?


This^^^^^^
I saw $100,000's in lab equipment go up in magic smoke, MWBC and neutral came off.


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## Veteran Sparky (Apr 21, 2021)

1. Patient Care requires redundant Ground. What you are describing is a multi branch. If you are going off plans, I would guarantee they require dedicated neutral. 2. Meaning all wires except equipment and redundant ground are current carrying and all those have to be de-rated if running more than 3 in any size conduit.


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## greenpro (Feb 21, 2021)

craigdj87 said:


> I'm not understanding 310.15 E.
> I want to run 9 hots on 3 3pole breakers with 3 Neutrals in a 3/4-inch EMT. Derating at 70% which brings me down to 21 amps. So, I'm good there. Do I count the Neutrals or not?
> 
> Thanks
> No neutrals do not count because they only will carrying the unbalance load.Look like you are running multi wire branch circuits,(three single phase sharing the neutral)


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## Veteran Sparky (Apr 21, 2021)

Architect is supposed to designate the area. What category is it 1,2,3? Multi wire circuits not allowed for patient beds for Cat 1 and 2. Make sure you know what is required. As a rule we NEVER run multi branch circuits for 120v circuits. For dentist office you need to be looking in Art 517.

_*Primary health-care centre*_. A centre that provides services which are usually the first point of contact with a health professional. They include services provided by general practitioners, *dentists*, community nurses, pharmacists and midwives, among others.


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## Malywr (Jan 23, 2018)

Veteran Sparky said:


> 1. Patient Care requires redundant Ground. What you are describing is a multi branch. If you are going off plans, I would guarantee they require dedicated neutral. 2. Meaning all wires except equipment and redundant ground are current carrying and all those have to be de-rated if running more than 3 in any size conduit.


He de-rated it cams 21A x 9 conductors in conduit


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## Veteran Sparky (Apr 21, 2021)

Malywr said:


> He de-rated it cams 21A x 9 conductors in conduit


I presume 20a breakers feed your lighting. 9 current carrying conductors is 70% de rate. In order to put wires on 20a breaker you would need to use #10 from Ampacity chart 167deg which is 35a. 35x70%=24.5A. If you ran 12, it would not comply because 25x70%=17.5.


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## Almost Retired (Sep 14, 2021)

Veteran Sparky said:


> I presume 20a breakers feed your lighting. 9 current carrying conductors is 70% de rate. In order to put wires on 20a breaker you would need to use #10 from Ampacity chart 167deg which is 35a. 35x70%=24.5A. If you ran 12, it would not comply because 25x70%=17.5.


you derate for no. of conductors from the Maximum ampacity
in my book 12THHN is 30amps * 0.7 = 21 amps


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## Almost Retired (Sep 14, 2021)

Almost Retired said:


> you derate for no. of conductors from the Maximum conductor ampacity
> in my book 12THHN is 30amps * 0.7 = 21 amps


the breaker panel has many more wires than 20 in it
you dont derate inside the panel
why would you start at the breaker temp rating to derate inside the conduit ?


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## Veteran Sparky (Apr 21, 2021)

Almost Retired said:


> the breaker panel has many more wires than 20 in it
> you dont derate inside the panel
> why would you start at the breaker temp rating to derate inside the conduit ?


You derate based on the circuit protection size. That is the point. Panelboards have a fill max, however, they are not enclosed like the inside of a conduit. There is typically room for heat to dissapate in a panel. Not in a conduit. Wire insulation is based on heat. Most all connections in resi and commercial world are 167deg F terminations. So you are basing your amapacity off that chart Not 194. Meaning 12 is good for 25 max NOT Derated. If you use THHN it is still only rated for 167deg on breaker terminations. Most electricians don't derate or understand it.


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## Almost Retired (Sep 14, 2021)

guess im one of those that dont understand it then ...


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## Veteran Sparky (Apr 21, 2021)

Almost Retired said:


> guess im one of those that dont understand it then ...


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## Almost Retired (Sep 14, 2021)

Veteran Sparky said:


> View attachment 163787


i cant tell what that is a pic of ?


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## Veteran Sparky (Apr 21, 2021)

Almost Retired said:


> i cant tell what that is a pic of ?


Contacts on a motor starter. Merely showing that most connections we all deal with are only rated for 75C/167F.


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## Almost Retired (Sep 14, 2021)

Veteran Sparky said:


> Contacts on a motor starter. Merely showing that most connections we all deal with are only rated for 75C/167F.


ok


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## Veteran Sparky (Apr 21, 2021)

Almost Retired said:


> ok


Rule of thumb is under 100a your wire is rated for terminations in the mid range. 14-1awg and 140deg F
see NEC 110.14


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## Veteran Sparky (Apr 21, 2021)

I hope I am not being confusing. There is Temperature Adjustment, Ampacity Adjustment and Voltage Drop Adjustment.
All with there own rules. See 110.14 and 310 and 315 to start with.
I hope I am not being condescending...not my intention, only trying to help make us all better.


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## Slay301 (Apr 23, 2018)

Unless the circuit is perfect Loy balanced there will always be current on the noodle so go ahead and count them


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## Dennis Alwon (May 9, 2009)

If these are multiwire branch circuit then you don't count the neutral unless the loads are linear. In most cases they don't count however take heed to what others said about patient care areas.


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## paulengr (Oct 8, 2017)

Dennis Alwon said:


> If these are multiwire branch circuit then you don't count the neutral unless the loads are linear. In most cases they don't count however take heed to what others said about patient care areas.


Nonlinear. As in switching power supplies…basically all electronics. We should all but assume that’s everything but so far it is “linear enough” to ignore. There is simply no guidance on how to dreads for harmonics. NEC just makes a threat then leaves you hanging,


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## Malywr (Jan 23, 2018)

Almost Retired said:


> the breaker panel has many more wires than 20 in it
> you dont derate inside the panel
> why would you start at the breaker temp rating to derate inside the conduit ?


I far I understand J agree with Almost Retired 
Post #25 and #26


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## Malywr (Jan 23, 2018)

Malywr said:


> Sorry for auto correction
> I agree with Almost Retired
> Post #25 and #26


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