multiple conductors?

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new guy
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multiple conductors?

Post by new guy » Thu Jan 12, 2006 1:55 pm

If I am attaching a wire to a circuit that is going to carry current to a load, but my wire is too small for the amperage draw. Can I use multiple smaller wires all attached at the same place? Will they "Divvy" up the current and carry it without burning up??

jimandy
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Re: multiple conductors?

Post by jimandy » Thu Jan 12, 2006 2:26 pm

Yes. If you strip the insulation off of what is called "stranded wire" you will see that it is actually lots of small wires any one of which is not capable of carrying the rated current of the strand as a whole. But be careful as separate wires could break off at the solder points and then poof for the one that's left.
"if it's not another it's one thing."

Tommy volts
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Re: multiple conductors?

Post by Tommy volts » Thu Jan 12, 2006 3:38 pm

Beginner,

If your wires are all insulated, then the current through each wire will vary directly with the wire diameter (inversely with resistance). The potential difference across the branch from supply to load will be the same across each of the individual conductors. In short the current will be "divvied" up so that the larger diameter wires take most of the current.

The question then becomes how much current is running through each wire. 20 gauge wire is good in the milliamp range, battery cable diamter wire is necessary if you are running 60 amps DC to a truck starter motor.

donwilson
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Re: multiple conductors?

Post by donwilson » Thu Jan 12, 2006 3:45 pm

That's right. Assuming you are using two wires the same gauge and length you should have 50% of the total current flow through each. A good thing to remember is that current divides in parallel and voltage divides in series. For example, I sometimes test 240V traffic light outputs from solid state relays for international clients. I don't have 240V bulbs handy so I use two 120 volt bulbs in series. The voltage is divided so they do not burn up.

<small>[ January 12, 2006, 03:46 PM: Message edited by: Don Wilson ]</small>

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haklesup
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Re: multiple conductors?

Post by haklesup » Thu Jan 12, 2006 4:03 pm

This is a very common practice WRT the pins on an IC device. Many higher pin count devices have over 50% of all pins as power and ground connected in parrellel both inside and outside the IC package.

It is also common in the card slots in your PC and for cabling where one large conductor would make the cable too inflexible.

Robert Reed
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Re: multiple conductors?

Post by Robert Reed » Thu Jan 12, 2006 6:13 pm

Beginner
There are a lot of definitions for current carrying capacity such as "free space"can be quite high where as "bundled" will be much lower. Also the rated current capacity even though met in any situation may still not meet your circuit requirements. Consider a LONG # 12 gauge wire carrying a 20 amp load and dropping 2 volts in the process. Even though the wire is adequate size for that load, it will affect different circuits in different ways i.e.--240VAC supply--2 volts is no big deal; 12 volt supply--2 volts is a problem. Just remember that wire capacities are there only to protect the wire and not neccesarily for your circuits operatiopn.

dyarker
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Re: multiple conductors?

Post by dyarker » Thu Jan 12, 2006 7:47 pm

All true, and often done.

But if you're talking about 120/220V mains wiring in your house don't do it. Please, please don't.

Cheers,
Dale Y

Dean Huster
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Re: multiple conductors?

Post by Dean Huster » Fri Jan 13, 2006 4:36 pm

Yes, the situation Dale mentions is against the electrical code. Our first house had an electric furnace and the house was built by the owner who was an idiot. He ran THREE parallel 240v #12 lines back to power the furnace and should have been using a single #4 run.

The bottom line would be, if you can afford and/or live with the destruction and loss of life and property resulting from one or more of the paralleled lines opening up, it's theoretically do-able -- just not very smart.

Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

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