NEUTRAL WIRE

[lenardchristian]

Can we run neutral conductors in a dedicated conduit? The 3-phase wires (3-1/C 2) are already existing but the neutral wire is only 1-1/C 12. I want to change the neutral wire to a 1-1/C 2.

[ February 09, 2005, 10:24 AM: Message edited by: lenardchristian ]

 

[roger]

Re: NEUTRAL WIRE

No, and with out going into other reasons, just read 300.3(B)

Are you really an Electrical Designer?

Roger

 

[petersonra]

Re: NEUTRAL WIRE

You could, but I seem to recall that all the circuit conductors have to be run together to meet code.

 

[roger]

Re: NEUTRAL WIRE

Bob, if these are metalic conduits would you still say you could?

Roger

 

[petersonra]

Re: NEUTRAL WIRE

Originally posted by roger:
No, and with out going into other reasons, just read 300.3(B)

Are you really an Electrical Designer?

Roger

Don't be too harsh. There are a LOT of people with the title electrical designer who are basically really drafters.

Where I used to work, we (somewhat harshly I must admit) sometimes refered to them as human xerox machines, as thir job was basically to copy the engineers' hand sketches onto drafting paper and make it presentable. No thinking was expected, or even encouraged.

One of my favorite stories is this. One time I put some special instructions on some sketches that I gave to a drafter. It started out "Note to drafting". You are probably going to be able to guess what was very neatly lettered on the drawing I got back.

These days no one can afford to do it that way anymore. So the guy who used to be called a drafter is now a designer and expected to do a fair amount of the thinking him/herself. Sadly, often these guys have received no additional training or education to go along with their additional responsibilities. Even scarier, they often have no effective engineering supervision over their activities.

 

[petersonra]

Re: NEUTRAL WIRE

Originally posted by roger:
Bob, if these are metalic conduits would you still say you could?

Roger

Note I said it would not meet code. That does not mean something cannot be done. The only thing preventing it is the recognition that it is almost always best to follow the code, since it has been proven over many years.

If someone does not understand the baisc reasons behind why these things are in the code, it does little good to go into them. The only thing you can do is say "it does not meet code" and leave it at that.

<added> did you notice in his post the phase conductors are #2 and the neutral #12? Is this code?

[ February 09, 2005, 10:47 AM: Message edited by: petersonra ]

 

[roger]

Re: NEUTRAL WIRE

Bob, I must ask, who seals the design, wouldn't they actually be the person to pose this question too?

Roger

 

[roger]

Re: NEUTRAL WIRE

Bob, don't you see an inductive heating problem if this were done in metalic conduit? There would also be a good chance of EMF (net current) issues if run in plastic that may not be side by side in close proximity the entire length of the run.

Roger

[ February 09, 2005, 10:50 AM: Message edited by: roger ]

 

[petersonra]

Re: NEUTRAL WIRE

Originally posted by roger:
Bob, I must ask, who seals the design, wouldn't they actually be the person to pose this question too?

Roger

I would think so. But note my comment about the endemic lack of effective engineering supervision.

 

[petersonra]

Re: NEUTRAL WIRE

Originally posted by roger:
Bob, don't you see an inductive heating problem if this were done in metalic conduit? There would also be a good chance of EMF (net current) issues if run in plastic that may not be side by side in close proximity the entire length of the run.

Roger

You seem to be missing my point. I don't think it is a good idea to do what he is proposing.

But I don't believe I can give him a succinct reason why, other than it does not meet code.

<edited to correct spelling>

[ February 09, 2005, 11:34 AM: Message edited by: petersonra ]

 

[megloff11x]

Re: NEUTRAL WIRE

Electrical Engineering spans everything from power distribution, to industrial wiring, to machine wiring, to circuit board design and layout, to programming, to Telecomm, to intergrated circuit design, to...

A person with such a degree may be a jack of all trades, or may be a specialist in one narrow area. 99% of the time, this area of specialty is NOT wiring buildings, machines, or power grids. I know EE's who don't even know how to solder or strip wire, but it's not their job to solder or strip wire. If they got drafted to do it, they'd have to learn just like everyone else did.

I personally find the NEC to be more law than anything else. They say that Naval regulations are written in blood, and to a lesser extent the NEC may be as well. The NEC is a collection of guidelines that if followed, will not result in burnt equipment or homes, or electrocuted people.

It is also LONG, it spans dozens of tomes, and like the law, it can be difficult to read and interpret correctly, especially if you have unique circumstances, which engineers usually do. Also like the law, there are contradictions, and exceptions, and wiggle room. And there are cases when it is NOT the safest course - there are other factors besides where the electrons go to consider.

An Engineer or Scientist usually does not go by "the code says so." He or she wants to know the backstory.

If you get a seemingly dumb question, answer it anyway.

What would you do if you got drafted to do an oddball boiler calculation; the steam part, not the wires to it part? You'd ask a boiler guy if you couldn't find the straight and skinny in a pile of boiler books.

 

[roger]

Re: NEUTRAL WIRE

megloff11x, if I had to design a boiler and new nothing about it, I wouldn't call myself a Boiler Designer either.

So with out using the NEC as a reason, what is your answer to the question? You can expand on my reasons if you would like.

Roger

 

[69boss302]

Re: NEUTRAL WIRE

I'd just like to make a comment. There are to many times that people like this "electrical designer" are put in the spot where they are told to just make what they have work. They have no clue themselves of why it won't work just as you have stated your not sure why it's just in the code. I think it is great that he at least sought some sort of advice or reason if it is correct. He probably has some boss standing over him that has an MBA or something like that and just sais make it work, my numbers have to match out and you can't buy extra stuff just the minimum.

 

[roger]

Re: NEUTRAL WIRE

Originally posted by 69boss302:
They have no clue themselves of why it won't work just as you have stated your not sure why it's just in the code.

Who stated that?

In this particular case the reason it is in the code is truly based in theory and the physics with it.


Roger

 

[charlie b]

Re: NEUTRAL WIRE

I feel the need to enter this fray. I'll start by coming to the defense of ?Electrical Designers.? Several of my previous companies used that phrase to denote persons who (1) Started their careers as drafters, (2) Learned the techniques and rules of electrical design through training and on-the-job experience, and therefore (3) Receive assignments of increasing responsibility, including making design choices. I have always considered such people to be valuable members of a design team. But like all of us, they still have much to learn. Therefore, I suggest we show them the same kindness and patience that we would ourselves desire to receive.

Originally posted by petersonra: . . . . did you notice in his post the phase conductors are #2 and the neutral #12? Is this code?

No it?s not. I am sure that is why Mr. Christian wants to replace the #12 with #2. In fact, although the neutral current is limited to the unbalanced current in the phase conductors, there may be time periods during which the only things turned on are on one or two phases, in which case the neutral carries a full load current. I can?t imagine why anyone thought a #12 would suffice here.

Originally posted by roger: I must ask, who seals the design, wouldn't they actually be the person to pose this question too?

Not all design processed require an engineer?s seal. I once worked for an electrical contracting company that had its designers send drawings directly to its installers. For those cases in which the client or the local authority required sealed drawings, the work would be supervised by a PE.

Originally posted by petersonra: But I don't believe I can give him a succinct reason why, other than it does not meet code.

I believe I can, two succinct reasons, in fact. All conductors of the same circuit must be in the same conduit (or in the case of parallel conduits, each conduit must contain a full set of phase, grounded, and equipment grounds) because:

Reason #1:</font>

• <font size="2" face="Verdana, Helvetica, sans-serif">The magnetic field generated by any single wire in the set will be essentially cancelled by the magnetic fields generated by the other wires in the set. This is what Roger had alluded to, and Bob did not disagree. To install one phase in its own conduit, or to install a neutral in its own conduit, would generate a significant local magnetic field. This could influence electronic equipment in the vicinity, and could cause heating of the conduit itself (if it is made of a magnetically-permeable material).</font>

<font size="2" face="Verdana, Helvetica, sans-serif">
Reason #2: </font>

• <font size="2" face="Verdana, Helvetica, sans-serif">An electrician performing a future modification or upgrade could come across this single conduit with only one wire, and noticing that that wire is connected to the panel?s neutral bar, might conclude (incorrectly) that it is an unnecessary spare wire and that it may be safely disconnected. The only safe way to work on a circuit is to know where all the wires are, and to know how to turn them all off at the same time.</font>

<font size="2" face="Verdana, Helvetica, sans-serif">

 

[roger]

Re: NEUTRAL WIRE

I don't know why, but I think my first post which included a simple question (maybe to direct of one) was meant to belittle Lenard, it was not.

I should have put that to rest in my third post.

Roger

 

[69boss302]

Re: NEUTRAL WIRE

Thank's Charlie b, excellent explanation. Every time I have ever tried to explain that to people my tongue get's tied up and they just can't understand why a pipe with wires in it would heat up. I guess it's because the MBA just teaches them how to count.

Roger I'm sorry if I sounded to strong myself, I just don't like to see somebody that is trying to do the right thing get jumped on. Especially when I can relate to his situation and can feel the guy standing over my shoulder saying he doesn't care just do what he tells you. These guys need explanations so that they can explain it to their boss or even at least feel comfortable enough to take a stand and tell their boss no because it is just unsafe.