Combining small gauge wire to make large gauge?

TConnolly · Feb 13, 2009

But Terry, with all due respect, I think you're missing the point. I don't think the reason for 310.4 has anything to do with voltage drop. The code has an exception for large wires (I imagine for mechanical reasons as 2" diamter wire would be a lot harder to work with than several 500MCM wires) so it makes it clear what the required condition is for smaller gage wires.

There are also other reasons besides voltage drop for using parallel conductors, one such example is high power high frequency applications.

I've had my rants about how the NEC is written myself.

Derek · Feb 13, 2009

Terry Woods said:
Alaric,

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.

I agree that there are things in the NEC that take more than
a casual read. Section 250 is still a complete nightmare to most people even though over the last 6 years it has gotten better.

The NEC is in the awkward position of trying to walk a thin line
between setting a minimum standard and proper design which
it has no way of foreseeing every possible circumstance.
Maybe that justifies some of the opaque language but who knows.

The most common problems I see is motors being too far from their drives, power factor and harmonics.
Not covered under the NEC but real problems.

You could make the argument if we left all design and installation to people
that were trained engineers and electricians with
a serious commitment to safety we would not need
any of the rules. The reality is both make mistakes.

I have been doing this stuff a long time and I still
manage to get wrote up once a year or so.

LJBMatt · Feb 14, 2009

Terry Woods said:
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.

Terry,

I agree clarifications would be nice but as someone who works with people directly involved in writing standards when you get a lot of engineers, not being specifically technical writers it's hard to satisfy the needs of what everyone is looking for. When I open the NEC (I also have the handbook which is worth the extra $) I read it as though it is trying to prevent fires and hazards against people and equipment. I don't look into it for design criteria, but only to check that my designs meet their code. Everyone interprets the code in their own way and I've had my share of experiences with different public inspectors and their demands. It would be nice to have things simplified and clarified but I don't think we'll ever see that happen. If you can buy the NEC Handbook. Very helpful in explaining the intent of the codes written.

Tark · Feb 17, 2009

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

The NEC does cover voltage drop. Off the top of my head I think it's a max of 5% between the service and the final device.

LJBMatt · Feb 17, 2009

I thought that was for motor and power loads, not all encompassing.

Tark · Feb 17, 2009

The NEC does talk about voltage drop and says that the total voltage drop of the feeders and branch circuits to the farthest outlet should not exceed 5%.

The NEC's definition of an outlet is not that of a receptacle but any point at which current is taken to supply utilization equipment, so an outlet is pretty much all encompassing.

However, the NEC talks about voltage drop in FPNs (Fine Print Note), FPNs are not mandatory to the Code and are in the Code for informational purposes.

So technically you could exceed a 5% voltage drop, but then that's not a very smart thing to do.

theDave2 · Feb 18, 2009

LJBMatt said:
I read it as though it is trying to prevent fires and hazards against people and equipment.

That pretty much paraphrases 90.1(A) Purpose.

Sergei Troizky · May 11, 2011

Derek said:
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.

Couple question about this old post subject.
What document has been quoted here?
If "each individual conductor is sufficient to carry the entire load current shared by the parallel conductors", then what may be the need in the parallel conductors?

oldnerd · May 11, 2011

My best advice is buy some wire....OR,
Parallel the wire and go the heck on unless you plan on having the inspecctor down to look at it.

Sergei Troizky · May 11, 2011

oldnerd said:
My best advice is buy some wire....OR,
Parallel the wire and go the heck on unless you plan on having the inspecctor down to look at it.

I did not ask for advice on the subject; actually I never do parallel wiring myself.
I only was curios about ... see the question 2.

rguimond · May 11, 2011

downey18 said:
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.

I don't think there would be any problem is the individual wires were stripped along their full length, twisted together and insulated. After all, wouldn't that just make it a stranded cable?

jkerekes · May 11, 2011

rguimond said:
I don't think there would be any problem is the individual wires were stripped along their full length, twisted together and insulated. After all, wouldn't that just make it a stranded cable?

I've seen enough badly wired and unsafe control cabinets! Do it the right way with the right cable and according to code.

Sergei Troizky · May 11, 2011

I am exactly quoting a code, and my question is:
What reason for wiring extra parallel conductors is supposed in the quoted code, if each individual conductor must be "sufficient to carry the entire load current shared by the parallel conductors"?
Good wiring practice is out of the question scope.

Andy6 · May 11, 2011

Alaric said:
There are also other reasons besides voltage drop for using parallel conductors, one such example is high power high frequency applications.

Here are a couple.

What I'm thinking is, basically the NEC dosen't want you to use conductors in parallel simply to handle higher currents. Pretty much any other reason you can think of is fine.

kamenges · May 11, 2011

Originally posted by Sergei Troizky:

What document has been quoted here?

That appears to be from the 2008 copy of NFPA 70, the U.S. National Electrical Code. It doesn't look like the 2005 version and the 2011 version is re-organized, moving the content of 310.4 to 310.10(H).

Originally posted by Sergei Troizky:

What reason for wiring extra parallel conductors is supposed in the quoted code, if each individual conductor must be "sufficient to carry the entire load current shared by the parallel conductors"?

Andy6's quote of Alaric lists both reasons given in the 2011 NEC handbook. I can't think of any others myself.

Keith

Combining small gauge wire to make large gauge?

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