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Old February 11th, 2009, 03:49 PM   #1
downey18
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Combining small gauge wire to make large gauge?

This is more of a power question rather than a PLC specific question but it is part of my PLC panel. I had to upgrade from a small 4A 24VDC power supply to a 10A 24VDC power supply. I only have the 22gauge wire available. My question is can I wrap three 22gauge wires together so the ends of both sides are terminated together to handle this new 10A source? In theory this would be the same as increasing the gauge of a wire but as I've found many times, nothing ever behaves the same as in theory.
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Old February 11th, 2009, 04:17 PM   #2
jrwb4gbm
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This is doable and allowed on existing (not new) control wiring installations below 50 volts I think, someone correct me if this is wrong. I would de-rate the ampacity to about 70% of the expected to be safe. You might find something in the NEC code book that will give you a better and more accurate answer.
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Old February 11th, 2009, 05:06 PM   #3
Derek
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Quote:
Originally Posted by downey18 View Post
This is more of a power question rather than a PLC specific question but it is part of my PLC panel. I had to upgrade from a small 4A 24VDC power supply to a 10A 24VDC power supply. I only have the 22gauge wire available. My question is can I wrap three 22gauge wires together so the ends of both sides are terminated together to handle this new 10A source? In theory this would be the same as increasing the gauge of a wire but as I've found many times, nothing ever behaves the same as in theory.

310.4 Conductors in Parallel.
(A) General. Aluminum, copper-clad aluminum, or copper
conductors of size 1/0 AWG and larger, comprising each
phase, polarity, neutral, or grounded circuit conductor shall
be permitted to be connected in parallel (electrically joined
at both ends).
Exception No. 1: Conductors in sizes smaller than 1/0
AWG shall be permitted to be run in parallel to supply
control power to indicating instruments, contactors, relays,
solenoids, and similar control devices, or for frequencies of
360 Hz and higher, provided all of the following apply:
(a) They are contained within the same raceway or
cable.
(b) The ampacity of each individual conductor is sufficient
to carry the entire load current shared by the parallel
conductors.
(c) The overcurrent protection is such that the ampacity
of each individual conductor will not be exceeded if one
or more of the parallel conductors become inadvertently
disconnected.

725.49 Class 1 Circuit Conductors.
(A) Sizes and Use. Conductors of sizes 18 AWG and 16
AWG shall be permitted to be used, provided they supply
loads that do not exceed the ampacities given in 402.5 and
are installed in a raceway, an approved enclosure, or a
listed cable. Conductors larger than 16 AWG shall not supply
loads greater than the ampacities given in 310.15. Flexible
cords shall comply with Article 400.
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Old February 11th, 2009, 05:25 PM   #4
theDave2
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Yes, you may do it. AFAIK, NEC does not apply much for wiring INSIDE a control panel except for motor controllers, over current protection and a few other things, however NFPA70 does.

About the only NEC code you might violate is often quoted 110.3(B): Installation and Use. "Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling."

Which simply means that the manufactures directions can't be violated. Like if you have only one terminal on the P/S and the mfg. says to place only one wire there and you place two wires under the terminal, that would violate the listing.

That said, sometimes ya got to do what ya gots ta do. As long as it's safe.


Don't forget to add wires to the 0v return to the P/S.

-Dave
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Old February 11th, 2009, 05:41 PM   #5
theDave2
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Derek: Take a look at 310.1 Scope. Since they "form an integral part of equipment" I'll say 310 doesn't apply.

I'll say the same using 725.1 Scope.

And just for grins, I'll bet the AHJ will allow it.

Maybe we should move this over to the MikeHolt.com forum ?
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Old February 11th, 2009, 05:47 PM   #6
Derek
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Quote:
Originally Posted by theDave2 View Post
Yes, you may do it. AFAIK, NEC does not apply much for wiring INSIDE a control panel except for motor controllers, over current protection and a few other things, however NFPA70 does.

-Dave
Once it leaves the manufacturer....
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Old February 12th, 2009, 08:31 AM   #7
Kent Hostetler
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I am curious.

Why are you limited to using three existing 22awg conductors? Why is there no other wire available where you are?

Kent

Last edited by Kent Hostetler; February 12th, 2009 at 08:33 AM.
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Old February 12th, 2009, 03:23 PM   #8
Terry Woods
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Damn, I hate the way the NEC is written!

This has nothing to do with the original post. It's just a rant on the NEC.

Having been a Technical Writer for many years in the past I've always hated the way that damned NEC is written! It's not so much what they say as much as what they don't say. Case in point...

310.4 Conductors in Parallel.
(b) The ampacity of each individual conductor is sufficient
to carry the entire load current shared by the parallel
conductors.

This would seem to be kind of a... Huh? If each wire is capable of carrying the load then why use parallel wires in the first place???

All they had to do was include a statement indicating that parallel wires are allowed for the purpose of reducing the voltage drop.

But even then... what happens if all but one of the parallel wires happens to open?


Nevermind.
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Old February 13th, 2009, 10:30 AM   #9
downey18
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Quote:
Originally Posted by Kent Hostetler View Post
I am curious.

Why are you limited to using three existing 22awg conductors? Why is there no other wire available where you are?

Kent
Well at the time we only had the small gauge wire but the question was more for my own curiosity. I appreciate everyone's input and for the references to the NEC. I tried checking it but I'd like to agree that the wordage is pretty confusing.
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Old February 13th, 2009, 10:31 AM   #10
TConnolly
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Quote:
Originally Posted by Terry Woods View Post
This has nothing to do with the original post. It's just a rant on the NEC.

Having been a Technical Writer for many years in the past I've always hated the way that damned NEC is written! It's not so much what they say as much as what they don't say. Case in point...

310.4 Conductors in Parallel.
(b) The ampacity of each individual conductor is sufficient
to carry the entire load current shared by the parallel
conductors.

This would seem to be kind of a... Huh? If each wire is capable of carrying the load then why use parallel wires in the first place???

All they had to do was include a statement indicating that parallel wires are allowed for the purpose of reducing the voltage drop.

But even then... what happens if all but one of the parallel wires happens to open?


Nevermind.
As long as the wire can carry the full amperage, voltage drop is an engineering concern not a code concern. Parallel conductors are allowed only for wires 1/0 (70mm2) and larger. Large wires can be difficult to install and connect and parallel conductors are often used in those situations. For everything smaller, when parallel wires are used, each individual wire has to be able to carry the full ampacity of the circuit. Unless the parallel conductors are all the same length and each connection is of equal quality then the current is not going to divide equally among the parallel conductors, the code takes the safe approach.
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Old February 13th, 2009, 03:12 PM   #11
Terry Woods
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Damn, Alaric...
Have you been taking time off from writing for the NEC???

310.4 Conductors in Parallel.
(A) General. Aluminum, copper-clad aluminum, or copper conductors of size 1/0 AWG and larger, comprising each phase, polarity, neutral, or grounded circuit conductor shall be permitted to be connected in parallel (electrically joined at both ends).

Exception No. 1: Conductors in sizes smaller than 1/0 AWG shall be permitted to be run in parallel to supply control power to indicating instruments, contactors, relays, solenoids, and similar control devices, or for frequencies of
360 Hz and higher, provided all of the following apply:

(a) They are contained within the same raceway or cable.

(b) The ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.

(c) The overcurrent protection is such that the ampacity of each individual conductor will not be exceeded if one or more of the parallel conductors become inadvertently disconnected.


Alaric, you said...
As long as the wire can carry the full amperage, voltage drop is an engineering concern not a code concern.

So... electricians are not to be bothered by something as consequential as voltage-drop?

Parallel conductors are allowed only for wires 1/0 (70mm2) and larger. Large wires can be difficult to install and connect and parallel conductors are often used in those situations.

This part is clearly stated and makes sense in terms of the physical limitations of larger cables. Reasonably it doesn't require that each parallel cable be capable of carrying the full load. At this point it seems to preclude the use of parallel wires for smaller guages simply because they are, after all, more flexible.

For everything smaller, when parallel wires are used, each individual wire has to be able to carry the full ampacity of the circuit.

Yeah, I can see that it says that. But can't you see that it is saying that smaller wires can be paralleled but only if each individual wire is capable of working properly without any parallel wires. Which is to say... we are allowed to use parallel wires only if each of the extra wires are redundant... as in... you really don't need the extra wires at all. You can use 'em, but only if you don't need 'em!

Unless the parallel conductors are all the same length and each connection is of equal quality then the current is not going to divide equally among the parallel conductors...

Yeah, and the NEC almost said so in... "...provided all of the following apply: (a) They are contained within the same raceway or cable."

..., the code takes the safe approach.

Gee... taking a position of no-position... as in... I'll support the idea of doing something, but only if doing that something causes no harm and at the same time doesn't need to be done anyway. Yeah, that's safe, very safe.

So, in the end, as far as the electrician - who is not to be concerned with voltage drop - is concerned, why in the world, under these constraints, would he consider paralleling a smaller wire (less than 1/0 AWG) at all?

According to how this is written, the only legitimate reason that I can see to run a parallel wire of small guage (less than 1/0 AWG) is in the case where a particular wire is subject to constant flexing/vibration and thus vulnerable to breakage. In that case it might very well be advantageous to have redundant wiring.

If that is what the NEC is really thinking... then why in the hell doesn't it just say so?
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Old February 13th, 2009, 03:54 PM   #12
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You've got to remember the NEC is NFPA70 which at its core is focused on fire protection. To say voltage drop is a secondary issue to the NFPA is a true statement. You may have a system that is NEC complient but not work for your application. That is the engineer's problem not the NFPA. If you have a wire not able to handle a load and therefore starting a fire is a primary concern for the NFPA.
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Old February 13th, 2009, 04:03 PM   #13
Derek
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Quote:
Originally Posted by Terry Woods View Post
If that is what the NEC is really thinking... then why in the hell doesn't it just say so?
IMHO the NEC makes it pretty clear that it is not a "design handbook" but a set of minimum specifications. They don't
get into the realm of intent and purpose. This what EE's
get paid for.
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Old February 13th, 2009, 04:33 PM   #14
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Terrry, no reason to get defensive. Feel free to kick the NEC all you want. Just don't complain when you stub your toe. I was only attempting to explain some possible reasons why article 310 was written that way instead of the way you wanted it. I struggle with interpreting parts of the NEC myself. I have learned that when I don't understand something, but look for help in properly interpreting it, I can usually come to understand what the code actually intends instead of what I think it should say. The wording has been carefully chosen and reviewed by thousands of participants to say certain specific things for specific purposes, and it is under continuous review with three years for public comment and evaluation between updates. The revision process is open to the public, you may submit your ideas on how it should be worded to the NFPA.
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Last edited by TConnolly; February 13th, 2009 at 04:37 PM.
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Old February 13th, 2009, 05:42 PM   #15
Terry Woods
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Alaric,

I'm not slamming on you. It's just that your's is the usual response to the questions about this part of the code.


Alaric, LJBMatt and Derek,

As written, and without actually saying so, the code "implies" that you can use parallel wires... but only if you don't need them.

Don't you think this begs clarification? Especially for those electricians that are not working for an engineer (that be reality, don' cha know?).

A large number of electricians and engineers simply accept the NEC as gospel without questioning. Granted, it is the law of the land. But then again, as you say Alaric, the code is subjected to review every three years. Do you really have to wonder why? Certainly the code needs to address new electrical concerns... but a lot of effort is given to revamping (clarifying?) existing code.

My point is simply that, the simple inclusion of the voltage-drop concern, regardless of who is responsible for calculating it, would eliminate the issue.

But then Derek raises the issue of "intent and purpose"...
Let's see... the ground wire goes to the ground terminal (silver) on an outlet, while the hot wire goes to the hot terminal (gold). And... the code does not purport to dictate this based on the "intent and purpose" of maintaining the proper ground/hot relationship among outlets... is that right?

My point is simply that, regardless of "intent and purpose" argument, this is just one of the many articles that needs to be addressed and clarified by the review board for the section.

Rant done.
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