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Can AWG wire size be detrimental to an electrical load if it is extremly oversized?

Posted on 2014-10-05
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Last Modified: 2014-10-06
Hello,

A friend and I have differing opinions about what happens when a conductor is oversized for a particular application. This question is not to find out what the proper size of wire to use for an application. Let's say that a circuit requires  14AWG wire conductors but instead 4AWG is used. Would this oversizing of conductors affect the load in any way? The question would apply to a section of water pipe that is oversized. Say that a 100 foot run of pipe was to be all done in 3/4" pipe, but instead 2" pipe were used. I would contend that there would we no detrimental effect. One water drop in, one out the other end. With no drop in pressure from one end to the other. Back to electrical. One electron in one out the other end. As long is you are oversizing and not undersizing.

This would apply if you were wanting to use existing wiring that was for a larger ampacity load for a new device that would otherwise require a new electrical run. Example would be to power an outlet for a microwave or any other light load with old wiring going to an air conditioning unit. Say 6AWG downsized at the outlet to 10AWG or whatever is required for the terminals.  

Thank you,

Dan
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Question by:Geek-
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by:Thibault St john Cholmondeley-ffeatherstonehaugh the 2nd
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I think you are correct with your 'one water drop' analogy.
It doesn't specify the material the wire is made from (%ge copper etc.) Or the type of insulation and these would have an effect if there was any to be had.
There may be an issue if the wire ran close to electronic components or other wires as the distances might be critical, and there would definitely be changes if the wire is used to form a coil, but just as a connector I can see no reason to use a particular size as long as it is at least as large as specified.
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by:John Hurst
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Wire size is related to the load it can safely carry. 14AWG wire is safe to carry 15 amps of current. This is common house size wire and connects 15A outlets to the fuse box.

You can use thicker wire without a safety issue. So number 12AWG could work as well.

Here is the issue you might face:

A 15 amp circuit (breaker box) must have 15 amp outlets attached to it. Such outlets are made for 14AWG wire.  You could use 12AWG wire but it is harder to attach to the 15 amp outlets screws and may not go in the connecting holes in some outlets.

You could NEVER use 4AWG in this example above. It just would not fit.

You CANNOT put a high amp outlet on a 15 amp circuit to use a different outlet to accommodate the wire.

Truly, use the wire rated for the use. It really works better and, while bigger wire like number 12 will work, it does not offer any benefit.
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Dear Dan,

You are absolutely right.

The fact that we want to use higher size that will imply basically 2 things: higher costs, because the conductors are expensive, especially when we instal long cables, and the second is the difficulty of the end connection, no matter if we use lugs, nuts, bars, circuit breakers, switches, sockets...

Would be interesting to hear the arguments of your friend to sustain his opinion...
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by:Don Thomson
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Normally - the only detrimental aspect would be to your pocketbook.  With copper, aluminum or steel wire, the larger the diameter of the wire, (Lower AWG number) the less the measured resistance.  However, what the wire is being used for may change the answer to this question.  If you for instance used a 4 wire 14 gauge cable to hook up an ethernet device, The twist int the cable would not be possible to counteract the external interference that the large cable would pick up.  

Looking strictly  from an AC power handling capability, if you used an 8AWG  gauge cable with the proper circuit breaker for that size of wire where a 14 gauge wire was called for, should a problem arise where the device you have plugged in was overheating and started pulling 20 amps instead of 12-15 amps, you could damage the device.

As far as using a large copper pipe than required, the only real factor her is cost.
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by:Dave Baldwin
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While I'm sure that you could find some marginal case where it made a difference because of poor design, under more 'normal' circumstances the load limits the current, not the wire size.  Wire ratings for a particular size are for resistive loss and temperature.  If the wire run is longer than normal it would not be unusual to use a size larger to lessen the losses.
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by:garycase
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Absolutely no detrimental effect [except, as noted above, for the impact on your pocketbook :-) ].

The connectivity issue noted by John Hurst could be an issue if you used very significantly larger wire; but isn't likely to be a problem if you just step up a nominal wire grade size.   e.g. if you use 12AWG instead of 14AWG you won't have a problem; but if you used 10AWG or 8AWG you definitely could.    Just as you'd have a problem connecting a 2" pipe to 3/4" fixtures.    But, as with pipes, it's also easy to downsize to the appropriate gauge at the end, so you get the benefit of the higher gauge wire for the actual run.

Not only does it absolutely not hurt to use the higher gauge -- in fact, electrically it helps; since there's less resistance, so the run will be more efficient.    One other advantage:   If you, for example, use 12AWG runs, and later need to increase the capacity of the circuit; you can then safely switch to 20amp breakers and outlets without having to re-run your wiring.   It's best, of course, to "get it right" from the start; but it certainly doesn't hurt to have a bit of a "buffer".    This is particularly true if you're running the wire where it would be difficult to replace.    For example, we have a long run to our kitchen island that is through conduit in the foundation.    It's a 30amp circuit using 10AWG wire.   I'd really like to change to a 40amp breaker so we can put it a larger cooktop,  but 3 different electricians have all said they simply can't do it without major "surgery" (tearing up floors and walls), so when we redid our kitchen we simply stayed with the smaller cooktop.    If they had used 8AWG wire when the house was built (20 yrs ago) that would have been a very simple thing -- just have the breaker changed to 40amp [the service  to the house easily supports that].
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by:Geek-
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Hello All,

Thank you for your quick answers. My friend believes that if wire is too large that there won't be enough power to fill the line. When extra load is placed on the circuit it would not react fast enough.

The actual circuit that brought up the question is the use of  air conditioning wiring that is no longer in use. It is 6 AWG. It will be moved from it's current location to the kitchen. It will be repurposed for an electric oven that calls for a 30 AMP circuit. The distance of 60 feet would call for 10 AWG. Two sizes down should not make any difference. The breaker will be sized based on 30 AMP quoted by oven manufacturer. All conductors are copper. Wire will be connected with wire nuts in a j-box behind the oven.

Thanks Dan
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by:John Hurst
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if wire is too large that there won't be enough power to fill the line. When extra load is placed on the circuit it would not react fast enough.

Thank you for the update and I was happy to help. No, large wire does not cause slow reacting. Large wire places physical installation issues and the possibility of people believing they can draw more current when in fact the limit is placed at the breaker.
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by:viki2000
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" My friend believes that if wire is too large that there won't be enough power to fill the line. When extra load is placed on the circuit it would not react fast enough."
Well, then we need to find a proper explanation for your friend, good for his level of understanding, so he has no more doubts.
Tell him like this:
- The current means moving the electrons in conductor(s), the flow of electrons.
- You do not have to "fill" the line/the conductor in order to have enough at the end of the line where the load is connected. You only need as much current as the load requires.
- Higher sizes in cables/conductors means more available electrons to move from one end to another. So it is even better from conductivity point of view. The resistance, the impedance of the cable is lower value when the diameter of the conductor is higher.
http://www.regentsprep.org/Regents/physics/phys03/bresist/default.htm
http://en.wikipedia.org/wiki/Electrical_resistance_and_conductance
- You get hot conductors when too many electrons try to move on a low section of conductors, meaning are under sized. Over sized is better from electrical point of view. You never have chances to heat up the conductors, the conductivity is higher and the resistance of conductor is lower.
- Your friend needs to understand that is not necessary to "fill" the line. You may use only 1/10 of the line. It is OK. No harm for load or conductor. He needs to use the load as reference and not the line. The load dictates the current, the quantity of the needed electrons and based on that the line is dimensioned and the source, as well as the protection of the line/source, is chosen.
-It is the other way around: when the line is bigger size then the load reacts faster, because are more available electrons to flow, to move, to do the job.
And this is only a particular situation for low frequency, eventually high current.
Similar behavior we have for the low current and high frequency, so called Telegrapher's equations (http://en.wikipedia.org/wiki/Telegrapher%27s_equations ), but that's for you not for him. When you have high frequency or high current, then the electrons have different behavior: they start to flow more closer to the surface of the conductor and not so many in center of the conductor any more. Under such conduction the surface of conductor becomes important and therefore the size of it, because a simple wire/conductor, when is very long  and is used at low frequency and high current, behaves almost similar if it would be short and used at high frequency. Long wire and high frequency is worst. The wire has in fact impedance: resistance/conductance, capacitance,  inductance. The problem how a load reacts at the end of the line makes sense only when we have very long lines or high frequencies.
In your case, low frequency and short lines, only the minimum size diameter is important. The rest exists, but if you calculate it you will notice is negligible and have no importance of all.
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That's very long an technical for explaining to someone. The water pipe analogy is much simpler to follow.
Not enough water to fill the tube and it flows happily, think of drains.
Too much water and the flow is resisted, drains overflow, and in electrical terms this resistance/overflow is converted to heat which is a bad thing in a conductor.
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by:d-glitch
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Concur that oversize electrical conductors will work well albeit with certain cost and possible mechanical issues.

But the water pipe analogy really breaks down.

>>   Say that a 100 foot run of pipe was to be all done in 3/4" pipe, but instead 2" pipe were used. I would contend that
        there would we no detrimental effect. One water drop in, one out the other end. With no drop in pressure from
        one end to the other.

If water is flowing, there is a pressure drop along the pipe.  This drop gets smaller as the pipe gets larger.

If you need more flow, you need to increase the pressure or the voltage.  
An over pressured pipe will eventually burst.  An over current wire will eventually melt.

A 100 ft run of 3/4 inch pipe will hold 2.3 gal of water.  
A 100 ft run of 2 inch pipe will hold more than 20 gallons.

So, for example, you would have a real problem running oversize pipe for a hot water run.
"You have to let it run for a while."  would take on a whole new meaning.

There is no analogous problem with electrical wiring.
You would not want to use oversize pipe
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That's why I suggested drain pipe. No need to consider the temperature, this water is just flowing like electricity. It is not being a carrier for another form of energy like your water carrying heat. The pipe allows a certain amount if water and no more. Pour a bit less in and you get less out the other end. All you are suggesting by quoting the capacity of different sized pipes is that a fatter conductor can carry more current.
Using oversize pipe would have the same economical effect as using oversized wire, wasted money.
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by:viki2000
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Speaking about pipes, what would be then the equivalent of a "superconductor"?
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by:d-glitch
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You would need lossless mass flow.  So no viscous or frictional forces.'
Liquid helium does exhibit super fluidity.

     http://en.wikipedia.org/wiki/Superfluid_helium-4
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by:viki2000
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For semiconductors, particularly transistors, here is the analogy:
http://cds130.org/Transistors
http://www.satcure-focus.com/tutor/page4.htm
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