# applying conduit fill and voltage drop.



## KevinS (Mar 12, 2015)

I have 4-10 ton, 460v 3ph RTU's in a row. 
am wanting to hit 2- RTU's with one raceway. 
There would be 7 current carrying cunductors.( 2- 25 amp MCA, circuits plus a 120v service recept in each conduit) the longest run is 275'. the other is 235'
I know how to calculate for VD but im sketchy on applying derating to the VD calculation.
so using the 70% derate for 7 conductors
do I take the 25 amps load and divide by .7? and this would give me 35.7 amps.
then I would use 35.7 in my VD calc?
When applying derating cant we use the 90 deg column?


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## Dennis Alwon (May 9, 2009)

Yes use the 90C for VD.

10 awg is good for 40 amps. If you derate to 70% you will have an ampacity of 28amps. Of course you need top check if the 10 is good enough for the VD.

Probably best to do the VD first and I suspect that the conductor will be large enough for the load with the de-rating


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## Dennis Alwon (May 9, 2009)

I did a VD calc and came up with a #8. Obviously the #8 will be fine for the 25 amp load since I showed above that 10 awg was sufficient without the VD


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## KevinS (Mar 12, 2015)

I have two calculators for doing voltage drop calc's. one is by Electricalc Pro.. it says to use #8
the other is an app on my Iphone by southwire. it says to use #10?
75deg, 25a at 360v, 275' 
So,
25/ .7 = 35.7amps. this represents the MCA after derating is factored in. #10 is good for 40 amps in the 90 deg column.


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## Dennis Alwon (May 9, 2009)

25 amps is what you need your conductor to be capable of carrying. 40 amps time 70%= 28 amps. Not sure why you divided 25/.7

28 amps is enough for the load served but the VD seems to want a #8


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## KevinS (Mar 12, 2015)

because the load (25 amps) upsized 30 % is 35.7. 
conversely 30% of 35.7 =25 or 35.7 x .7 = 25

I like the way you did it though, makes sense.


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## Dennis Alwon (May 9, 2009)

You don't upsize the load. The mca of the unit has the 125% figured in it. So work with the 25 amps.

Your VD calc will be based on 25 amps, 3 phase , copper, 480 (460) volts. Using the furthest distance I get 8 awg so the de-rating really is not an issue


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## KevinS (Mar 12, 2015)

i have 3 VD calculator apps on my phone.
Cerrowire says #8
General Cable says #10
Southwire says #10


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## Dennis Alwon (May 9, 2009)

KevinS said:


> i have 3 VD calculator apps on my phone.
> Cerrowire says #8
> General Cable says #10
> Southwire says #10


What percentage drop are they using. I usually work with 3%.


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## glen1971 (Oct 10, 2012)

KevinS said:


> I have 4-10 ton, *460v 3ph* RTU's in a row.
> am wanting to hit 2- RTU's with one raceway.
> There would be 7 current carrying cunductors.( *2- 25 amp MCA, circuits plus a 120v service recept in each conduit*) the longest run is 275'. the other is 235'
> I know how to calculate for VD but im sketchy on applying derating to the VD calculation.
> ...


Is this ok in the US? I don't think we could pull that off north of the 49th, or at least I've never seen a 120 volt lighting circuit tied into a higher voltage (MCC or CDP) feeder conduit...


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## ponyboy (Nov 18, 2012)

glen1971 said:


> Is this ok in the US? I don't think we could pull that off north of the 49th, or at least I've never seen a 120 volt lighting circuit tied into a higher voltage (MCC or CDP) feeder conduit...



Yes it's allowed. Many times it will be avoided due to job specs and lots of people think it's forbidden but in the industrial world it's done every day. I don't go out of my way to do it but if it makes the project or run easier then I don't even think twice


Sent from my iPad using Tapatalk


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## KevinS (Mar 12, 2015)

Thanks for the help on this project. appreciate the feedback. This message board thing is new to me. cant figure out how to like a comment or quote a comment.


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## WyrTwister (May 2, 2015)

glen1971 said:


> Is this ok in the US? I don't think we could pull that off north of the 49th, or at least I've never seen a 120 volt lighting circuit tied into a higher voltage (MCC or CDP) feeder conduit...


 The way I read it , I think he means to pull the 125 VAC circuit in the same conduit as the 480 VAC conduit ?

Would not do that on a bet . We run a separate conduit for the 120 VAC circuit .

God bless
Wyr


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## Dennis Alwon (May 9, 2009)

WyrTwister said:


> The way I read it , I think he means to pull the 125 VAC circuit in the same conduit as the 480 VAC conduit ?
> 
> Would not do that on a bet . We run a separate conduit for the 120 VAC circuit .
> 
> ...



Yes, but the install is compliant


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## B-Nabs (Jun 4, 2014)

glen1971 said:


> Is this ok in the US? I don't think we could pull that off north of the 49th, or at least I've never seen a 120 volt lighting circuit tied into a higher voltage (MCC or CDP) feeder conduit...


Compliant in the US, violation in Canada.

12-904 (2) No raceway or compartment of a multiple-channel raceway shall contain conductors that are connected to different power or distribution transformers or other different sources of voltage, except where the conductors
(a) are separated by the metal armour or metal sheath of cable assemblies of the types listed in Table 19;
(b) are separated by a barrier of sheet steel not less than 1.34 mm thick or a flame-******ant non-metallic insulating material not less than 1.5 mm in thickness; or
(c) are used for the supply and/or control of remote devices, are insulated for at least the same voltage as that of the circuit having the highest voltage, and none of the conductors of the circuits of lower voltages is directly connected to a lighting branch circuit.


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## 480sparky (Sep 20, 2007)

WyrTwister said:


> The way I read it , I think he means to pull the 125 VAC circuit in the same conduit as the 480 VAC conduit ?
> 
> Would not do that on a bet . We run a separate conduit for the 120 VAC circuit .
> 
> ...


So you would also run separate conduits for the 208 and 277v circuits?


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## WyrTwister (May 2, 2015)

120/208 together .

480/277 together .

God bless
Wyr


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## NacBooster29 (Oct 25, 2010)

In the u.s. as long as the insulation is rated the same most is rated 600v or less. 
Seperate conduit for low voltage t stat, fa shutdown etc. 
Class 2 wiring


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## butcher733 (Aug 4, 2012)

Around here most would pull all of the circuits in a one inch conduit and not derate anything. They would worry to all hell about a little dog in an offset but wouldn't think twice about the fill or compliance.


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## Tactical Sparky (Sep 6, 2015)

butcher733 said:


> Around here most would pull all of the circuits in a one inch conduit and not derate anything. They would worry to all hell about a little dog in an offset but wouldn't think twice about the fill or compliance.


A whole lot of truth in this statement around most of the country.


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## eddy current (Feb 28, 2009)

Let me get this straight.
You can take two conduits, one from a 277/480 volt panel and one from a 120/208 volt panel, and join them at a j-box. Then from there all the conductors (both voltages from different panels) *all go into one conduit* out to your RTU's, lighting etc.

And this is a NEC compliant install? :blink:


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## Cow (Jan 16, 2008)

eddy current said:


> Let me get this straight.
> You can take two conduits, one from a 277/480 volt panel and one from a 120/208 volt panel, and join them at a j-box. Then from there all the conductors (both voltages from different panels) *all go into one conduit* out to your RTU's, lighting etc.
> 
> And this is a NEC compliant install? :blink:


Yes!:thumbup:

I almost always put a gutter over both my high and low voltage panels just so I can mix circuits from each panel in any conduit I choose. I really can't imagine making two penetrations in the roof just to feed a 480rtu and the 120v recep mounted on the side of it. One pipe makes more sense when all the wire carries the same 600v rating, right?


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## eddy current (Feb 28, 2009)

Not in Canada.


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## telsa (May 22, 2015)

Folks, we need to keep in mind that the Canadian scheme is ONE COLOR CODE ONLY.

Red, Black, Blue, White, Green 

That color coding is used at 208Y120 AND 600Y347.

%%%

The American coding scheme is 

Black, Red, Blue, White, Green 208Y120

Brown, Orange, Yellow, Grey, Green 480Y277

So, with the B.O.Y. colors being so obvious versus the BRBl scheme -- running them both in the same raceway is not a serious risk. All conductors are rated all the way up to 600 VAC.

The one factor -- that is probably never a factor in Oregon (?) -- is de-rating for heat -- as these are RTUs.


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## Cow (Jan 16, 2008)

eddy current said:


> Not in Canada.


You guys are missing out....


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## Jmcstevenson (Sep 11, 2010)

B-Nabs said:


> Compliant in the US, violation in Canada.
> 
> 12-904 (2) No raceway or compartment of a multiple-channel raceway shall contain conductors that are connected to different power or distribution transformers or other different sources of voltage, except where the conductors
> (a) are separated by the metal armour or metal sheath of cable assemblies of the types listed in Table 19;
> ...


 Wouldn't (c) allow a jb fed from multiple sources/voltages to feed, say, different V welding plugs? So long as the conductors are rated for the higher voltage wouldn't those be remote devices


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## eddy current (Feb 28, 2009)

Jmcstevenson said:


> Wouldn't (c) allow a jb fed from multiple sources/voltages to feed, say, different V welding plugs? So long as the conductors are rated for the higher voltage wouldn't those be remote devices


No. That is like for the controls for a motor, or the controls for lighting. 
Lets say you have a 600 v / 3 phase motor. You step down the voltage for the controls. All the wires can go in the same conduit out to the remote devices and motor.


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## Pete m. (Nov 19, 2011)

telsa said:


> The American coding scheme is
> 
> Black, Red, Blue, White, Green 208Y120
> 
> Brown, Orange, Yellow, Grey, Green 480Y277


We also need to keep in mind that this may be widely used in the U.S. but it is not based on the NEC.

The NEC does not mandate a particular "color code" based upon applied voltage.

Pete


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## don_resqcapt19 (Jul 18, 2010)

Pete m. said:


> We also need to keep in mind that this may be widely used in the U.S. but it is not based on the NEC.
> 
> The NEC does not mandate a particular "color code" based upon applied voltage.
> 
> Pete


But it does require that the conductors be identified as to phase and voltage if there is more than one nominal voltage system in the building, even if you are using completely separate raceways for each system.


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## bduerler (Oct 2, 2009)

I have an awesome conduit fill worksheet on excel if anyone wants one, just pm your email to me


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