Voltage Drop for more than 3 conductors?

Status
Not open for further replies.
D

dude454

Member
I have a inspector telling me that I cant run more than three conductors in a conduit without twisting my wires, even if I de rate, do to the impedance that is created by the additional wires. He says it causes to much voltage drop even in short runs.

Thought maybe this board might have a formula I can use to caculate voltage drop for more than 3 conductors in a conduit?
And maybe a technical way to explain to this inspector why he is wrong.

Looked in the code book but could only find formula up to 3 conductors.

Thanks
Ron
 
Re: Voltage Drop for more than 3 conductors?

Originally posted by dude454:
Thought maybe this board might have a formula I can use to caculate voltage drop for more than 3 conductors in a conduit?...............Looked in the code book but could only find formula up to 3 conductors.
Click to expand...
I am interested as to where in the code book you found this.

Try this, although I do not see any references to the number of conductors. :roll:

vdfrmla1.jpg
 
Re: Voltage Drop for more than 3 conductors?

Thanks for the table Bob I just wish it specified more than 3 conductors.

Ron
 
Re: Voltage Drop for more than 3 conductors?

Maybe 3? is being interpreted as 3-conductors? Three-phases=Three-conductors?

You can take the voltage drop for one conductor, and if the variables are identical on the other conductors you just use the same end result for all the similar conductors.

Or maybe it's not a 1? or 3? installation? Maybe it's one of those hybrids discussed in other previous threads?
 
Re: Voltage Drop for more than 3 conductors?

Wayne if has more than 3 conductors in a raceway, how many phase is that? ;)

Ron you are welcome for the table I will thank Scott T. for the table.

I would say the fact that the formulas do not include a variable for how many conductors are run together, that the number of conductors makes no difference, or such a small amount of difference it can be ignored.
 
Re: Voltage Drop for more than 3 conductors?

Bob,
I would say the fact that the formulas do not include a variable for how many conductors are run together, that the number of conductors makes no difference, or such a small amount of difference it can be ignored.
Click to expand...
you are absolutly right.

The effect of more than three conductors in a race way is already figured into the percentages listed in 310,15(B)(2)

As far as a formula for figuring voltage drop, there are never more than three current carrying conductors in a circuit.

Single phase is 2 x K

Three phase is 1.732 x K

I don't know what the Four, Five, Six, ect... phase calcs are. :D

Roger
 
Re: Voltage Drop for more than 3 conductors?

What do you mean by "more that 3 conductors in a
conduit"? Is that 1 conductor per phase, or 3 single phase conductors? Need to be more specific.
Actually when you twist 3 single phase conductors
together it reduces the inductance of the cables.
The accuracy of the voltage drop caculations
is not comprised by using the table shown above.
I assume you know that if voltage drop using one cable per phase = 1, then the voltage drop using 2 cables per phase = 1/2 and on 3 cables per phase = 1/3.

[ October 18, 2003, 11:20 PM: Message edited by: bob ]
 
Re: Voltage Drop for more than 3 conductors?

Originally posted by dude454:
<snip> Looked in the code book but could only find formula up to 3 conductors. Thanks
Ron
Click to expand...
Ron,
When you look in the code book which formula do you find?

Are you talking about running conductors in parallel to increase ampacity, or are you talking about running multiple circuits in one raceway?

Is this single-phase or is this three-phase?
 
Re: Voltage Drop for more than 3 conductors?

Thanks for the replies what we have is a 3phase pannel 120/208 and the inspector is saying you can only have a total of three conductors on different phases in the conduit, unless you twist the wires.
Even if you de rate wire.

Ron
 
Re: Voltage Drop for more than 3 conductors?

File a complaint and get a hearing on this matter. You will do all electricians a favor. This guy is a loose cannon, and needs to be disarmed.
 
Re: Voltage Drop for more than 3 conductors?

Dude have the inspector give you the code he's refering to. I have the 2002 NEC on CD rom and can do serches but I can not find any thing that would require twisting of the service wires. how in the world would you twist 500 MCM?
 
Re: Voltage Drop for more than 3 conductors?

Originally posted by hurk27:
how in the world would you twist 500 MCM?
Click to expand...
Wayne we already covered that over here.

Voltage Drop

Originally posted by iwire:
Originally posted by roger:
Then ask him where you can buy 500 mcm twisted pair,
Click to expand...
Come on Roger just pull 3 or 4 of them out across the floor, chuck them up in a cordless drill and twist em up. :D

It does not get difficult until 1000kcmil. :D
Click to expand...
Sounds like a great inspector. :roll:
 
Re: Voltage Drop for more than 3 conductors?

Dude, all kidding aside, this is nuts.

Think of any building with a three phase power.

The main service, all the feeders to remote panels and many times the feeders to equipment are 3 phase 4 wire + ground.

You will not find any of them twisted.

We do a lot of large services, 3 sets of parallel 600 kcmil, 8 sets of 500 kcmil or 10 sets of 600 kcmil, believe me these do not get twisted together before we pull them in the pipe.

On the contrary we strive for them to go in perfectly straight so there is no jamming of conductors against the walls of the raceways.

As for cable assembles like NM or MC I believe they are twisted so the cable can be bent easer.

If the conductors were not twisted and could not slide by each other it would be very difficult to bend the assembled cables.

Try to bend a piece of flat SE cable "sideways" and you will see what I mean.
 
Re: Voltage Drop for more than 3 conductors?

Originally posted by bennie:
File a complaint and get a hearing on this matter. You will do all electricians a favor. This guy is a loose cannon, and needs to be disarmed.
Click to expand...
Bennie once again you have hit it right on the head. The gentleman that posted this topic is one of a rare breed who will actually question authority. Think of those who won't or some poor apprentice who thiks this clown inspector is teaching him something!

In my state, I am required to carry a license, just like the installer is. I am just as succeptable to formal complaints with DOPL.

I would be willing to bet that this inspector is not certified to be inspecting electrical
 
Re: Voltage Drop for more than 3 conductors?

Dude
What size is the panel? Do you have more than one conduit run to this panel? Do you have more that 3 conductors in the conduits?
 
Re: Voltage Drop for more than 3 conductors?

Ryan, N.C. also has inspector classifications.

A class three covers all the bases and this comes after passing state exams for the certification and licensing.

My dealings with 99% of class three inspectors have been with mutual respect for one another.

Isn't it funny how the more knowledgeable someone is, the more likely they are to meet on even ground, and even admit a mistake. I guess this is a sign of being secure. :)

Roger
 
Re: Voltage Drop for more than 3 conductors?

Originally posted by dude454: I can?t run more than three conductors in a conduit without twisting my wires, even if I de rate, due to the impedance that is created by the additional wires. He says it causes to much voltage drop even in short runs.
Click to expand...
The Inspector is wrong. The impact on voltage drop of twisting wires is insignificant at the voltage levels you see inside a building. But more to the point, this question lies outside the scope of the NEC, and therefore outside the scope of the Inspector?s authority. It?s a design issue. Speaking as a designer, I refer the reader back to my second sentence. Speaking as a member of this forum, I?ll refer the reader back to a point made frequently in many threads that discuss similar cases: Have the Inspector cite the NEC chapter and verse that he is using to make this claim, or else disregard his comment.
 
Re: Voltage Drop for more than 3 conductors?

I'm closing this thread. There is a duplicate thread in the NEC area, so please continue the discussions there.
 
Status
Not open for further replies.
Top