Electrical wiring

William462 · Jul 21, 2008

I'm running a branch circuit out to my workshop, from the main breaker box in my house.
It's about a 30 foot run, all indoors, and will run from my main breaker box to a load center box in my garage. I could buy some 6 awg wiring, or perhaps I could use some of the 10 awg romex I already have lots of, but run two conductors in parallel to give me the 40 amp capacity I'm planning on. It will be a 120/240 volt circuit, single phase. As long as the conductors are properly color coded ( i.e. painted) at the ends, is there anything drastically wrong with using twin 10 gauge conductors instead of a single # 6 wire for each leg ? I'd use three 10-2 (with ground) lengths of romex. ( Be nice now, you "code" guys ! I'm just asking.)

JST · Jul 22, 2008

Generally, you are not supposed to parallel wire under 1/0, IIRC.... could be wrong on which, as I didn't look it up since a month ago. Point being, there is a lower limit to what size you can parallel.

You can look it up yourself, the NEC is available for viewing at the NFPA website.

deltaenterprizes · Jul 22, 2008

Thanks for the tip on NEC at NFPA web site.
My opinion,for what it is worth is that 2 parallel conductors maybe ,3 I don't think so,romex a no no.Conductor need to be same length,hard to do with romex.How are you going to secure 3 wires to insure current flows through all 3 all of the time,risky.
Is it worth it to risk your house and shop and contents?

JunkyardJ · Jul 22, 2008

Theoretically, it's possible.

The difference in current flow between them, even if the difference is a couple feet, will be pretty low IF they all make a good connection. IF you can get in the wall, and the ONLY thing standing in your way is the fact you have to BUY the wire, DO NOT run multiple 10ga wires. IF you get a bad connection, and your 10ga wire starts a fire, your insurance company is going to tell you to get bent if they find out!!! Cheap insurance, buying the proper wire, and doing it right if you ask me. If the wall was allready up, and the wire was behind the drywall, and it wasn't going to be subject to high current draw for long periods of time unattended, I'd say do what you want. Given the price of 30' of 6ga wire, I can't condone doing it if that's the ONLY reason. It's your house, and your butt, I wouldn't do it though. :dopeslap:

JST · Jul 22, 2008

Paralleling is fairly normal in larger power installations.... but that is with larger wire, which is easier to get "the same" as to length etc.

For any normal purpose, and for smaller wire, just get the right size and move on.

jim rozen · Jul 22, 2008

The other disadvantage to paralleling the tens, would be if they were enclosed
together in the same chase or conduit.

This would require de-rating for thermal reasons.

Wire's not that expensive, I likewise suggest you bite the bullet and get
exactly what you need. 1) you can use the tens elsewhere, 2) you will
have a professional installation you can enjoy looking at for a long time
in the future.

Jim

William462 · Jul 22, 2008

Ok, you've all convinced me not to run two conductors in parallel. I do already have some very nice #6 copper stranded insulated conductors I bought surplus. The trouble is that they are in approximately 15 foot lengths, and I'd have to splice them to reach. I suppose the code doesn't approve of splices in such cases either, right ? Are there junction boxes that qualify as an approved splice ? If all else fails, I'll just have to buy new wire, and cut back on the beer budget. ( My wife's beer budget, that is.) Thanks all !

Doug S. · Jul 22, 2008

Yes, you can splice in a proper junction box. It can easily be done legally.

However, thirty feet? Come on. Do this right.
Electrical installation is an area in which one should generally NOT cut corners, ESPECIALLY if you are asking questions about it. !

Also: 40amps? Is that what you plan to draw regularly or is it just what you want out in the shop?

#8awg can be used on a 40a circuit (40a circuit breaker, not name plate), letting you do this right, and save a few bucks. IMHO #8 stranded in a cable / romex will be easier to handle than the #10 solid conductor.

Regards,
Doug S.

RMeyers · Jul 23, 2008

JST said:
Generally, you are not supposed to parallel wire under 1/0, IIRC.... could be wrong on which, as I didn't look it up since a month ago. Point being, there is a lower limit to what size you can parallel.

You can look it up yourself, the NEC is available for viewing at the NFPA website.

Your correct min size is 1/0 must be same insulation, and the SAME length. and for what you want a bad idea. See NEC 310.4 2002.
If you want 8/3 NM (Romex®) your limited to 40 A overcurrent protection, if 8 AWG THHN/THWN is used in conduit then a 50 A overcurrent device can be used.

wippin' boy · Jul 23, 2008

me the 40 amp capacity I'm planning on.

RM's right
that only calls for #8 not 6

JunkyardJ · Jul 23, 2008

Yeah, but #6 isn't much more than #8.

If you're going to kill the beer budget, might as well do it for a real upgrade. #6 wire will allow 50 or 60 amps, and you'll be able to run a welder, or other high draw stuff in the future. I wouldn't skimp on the wire size if the box can handle the breaker size. It allows for future upgrades without hassle. :cheers:

RMeyers · Jul 24, 2008

Conduit is cheap insurance for future needs if it's oversized a bit.......

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