I have been told that significant electricity can be save if one upsizes the wiring by just one size. Is this true? As I'm not an electrician I assume this is true since there would be less resistance with a larger wire. Is there any definitive research stats on this subject? I've only found one article on this from the copper association. However, since they represent the wiring industry it may be suspect. TIA Mike

Given the fact that there are published tables that rate the current carrying capacity of wire, I find this to be unfounded if wiring is sized to the load (length of run, amps, environment, etc). Not to mention it would be common knowledge. Yes current will go up as temperature of the conductors rise, but that is an indicator of improper application of the components of the circuit (wrong size wire/ insulation, poor circuit protection/sizing, failing components). Our plant had an electric bill of over $300k last month (we do all of our heating with gas), if putting in place oversized wires were to help I have a feeling that I would be in for alot of OT from here to retirement.
I think you are probably correct in your interpretation based on its source.
Gabe
PS: Engineer at work couldn't stop laughing.

Amory Lovins mentioned this in a recent interview. He used oversized wire in the Zero Energy home he owns in Snowmass, CO. Funny engineer you have...

Resistivity and Conductivity

The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made. Experimentally, the dependence upon these properties is a straightforward one for a wide range of conditions.

The factor in the resistance which takes into account the nature of the material is the resistivity. Although it is temperature dependent, it can be used at a given temperature to calculate the resistance of a wire of given geometry.

The inverse of resistivity is called conductivity. There are contexts where the use of conductivity is more convenient.

I thought I'd qualify this by.... I'm no expert.  Just my thoughts on the subject...



How do you save money by having larger wires? You are charged by the amount of electricity you use, not how fast it goes through the wires. Unless of course you are saying that by using smaller wires you are somehow using more electricity.

Think of your wires like a hose or pipe and electricity like water. Imagine now that you then decide to get a glass of water and you turn on the faucet. Your faucet is regulated to allow only a certain amount of water through at a time. Your pipes would let a lot more water through, but the faucet only draws so much.

Similarly your appliances have a certain 'draw' or how much electricity they need. Electricity is the movement of electrons across a conductive surface (for simplicity sake). Changing the size of the wire only really changes the potential amperage (number of electrons) drawn on that circuit (which could be dangerous if you went too wild with it). Bigger wires are not more conductive (not any easier for for electrons to move), they just allows more electrons to move because it is bigger.

Hope this helps

john

electricity travels on the surface of the wire , not through its core. If you really want to capture the small losses that result from the resistance of the wire then increase the surface area of the wire. Instead of using a larger wire go to stranded wire. More wires, equal more surface area (conduction plane) resulting in a lower overall resistance consumption.

Either way the amount of energy you save by decreasing the resistance of the copper wire is going to be trivial. You are talking about energy in the form of electricty that is converted into heat in the wire instead of powering the load. Try holding an energized wire in your hand. How hot is it? The difference between the temperature of the room and the temperature of the wire is your energy loss.

If you upsized the wire in an entire home, it would result in saving less energy than is lost by air infiltration through a single unsealed outlet box in an exterior wall.

Electricity is not water and wiring is not plumbing.
Resistance is proportional to length and inversely proportional to cross sectional area.

You are charged not for the voltage(Volts) or the current(Amps) but for the power(Watts) -specifically the  number of  kilowatthours which is a measure of Watts used over an hour. Power in watts is equal to the Voltage times the Amperage.

Watt=Volt*Amp

and Amperage is proportinal to Voltage divided by Resistance(Ohms)

Amp=Volt/Ohm

Changing the wire size does not actually change the ability to draw current up the line, you've still got a breaker, usually 15 or 20 Amp, which is the same current limit you've got with wire sized to code.

What oversizing your wire will do is reduce the line resistance of your circuit. Any time you have a resistance in a circuit element be it a toaster a lightbulb or the wiring in your system, the element dispates power, this is why wiring will heat up at high current loads. Power lost along the line is wasted. Reducing the line resistance will reduce wasted power.

The skin effect at 60Hz limits the current to the outer ~8.5mm, that's about 1/3 of an inch.

So Cameron, does up-sizing reduce the resistance? If so, are any of the previous posts accurate in the estimate of a 10 year +/- payback time frame?

What about any savings generated with the use of an KVAR unit on the mains?

To respond to Mike's original post. I don't know that "significant electricity" can be saved, but there is a savings. Increasing wire size decreases the wire's resistance and as the resistance is decreased, the amount of lost energy is reduced. The energy saved is proportionate to the wire's resistance. If the resistance is reduced by a third, the wasted energy is reduced by a third.

I don't believe that there is a golden rule that can be applied that says it is always worth it to upsize the wire one size. I think upsizing depends on the application. There are times when it is not worth the cost and there are times that it is.

I think that Jamie's lost energy calculations are missing a factor of 2...the circuit length would be twice the length of romex used - hot conductor length plus neutral conductor length = 200'. This would result in twice the energy lost ($10.36 vs $5.18) and half the payback calculated (apprx. 5 years).

Using Jamie's example to illustrate my point. Say we change the installation to one installed in conduit.
- The cost of the conduit is the same as for #12 or #10 wire - so that's a wash.
- 200' of #12 wire costs $105 (based on Means-2006) and 200' of #10 costs $125. The additional cost of the #10 is about $20 (vs $51 for romex) and equates to a payback of approximately 2 years...that's not so bad.

If the load ran for only 8 hours a day, the payback would be 6 years and that wouldn't be such a good deal.

Mike, do you have a specific application?

I was wondering if this topic can be revisited.  I too have found the one article alluded to by Mike and I guess I am curious as to whether if building a new house it is worth the investment to use wire one size above code.

I can find the average home in America uses 11,000 KW per year, I can see that my current home has about 1500 linear feet of wire (3000 ft for calculation of resistance).  But I am unsure of how to calculate the diffence in KW losses across the two types of copper wires.  It appears that it is load dependent, so therefore what would be a typical load in northeast US?  Lighting, appliances, oil or gas furnace and hot water.  Seems that with some reasonable assumptions it could be determined if in new construction it is worth investing universally in larger guage wire.  Similarly, I guess we could calulate in individual circuits that have larger loads on them (kitchen appliances, furnace, dryer) and determine if some lines are worth additional investment.  Thanks for your thoughts.

Along these same lines does this effect motors in any way? In my case I have a 30 amp 240vac breaker feeding #10-3 line to my geothermal. The heat pump runs a long time when off peak starts, about 4 hours straight and the wire gets warm to the touch, not hot but you can tell it pulling a good amount. I checked it and it pull s about 18 amps running. What got me thinking about this is what is the voltage at the motor, I haven't checked yet, but as the voltage drops doesn't the motor increase in amperage draw? Doesn't that also shorten the life of the motor or make it less efficient? Also starting I would think a larger size would make all the motors start easier?

Going even further off topic, I don’t understand why it starts all the motors at once, my guess is it cost less, but it starts the big compressor motor, the 2 circulation pumps for the field, the circulation pump for the hot side and the circulation pump for the desuper heater. To me it would seem to be easier on everything to start all the small motors first, then the big one, even if thy were spaced out by a second or so the motor start hit wouldn’t be as bad.

Basically, yes, it does matter. V=IR still holds even for AC circuits (though you use the RMS voltage, 120, for this equation) P=I^2R.

So you do save energy using bigger wires. BUT, it is only economically efficient if a circuit is pulling 10 amps for hours each day. 10 amps at 120 Volts = 1.2 kilowatts!

So, think about it. Which circuits need multiple kilowatts? Well, in a typical house, only big loads count.
1. The compressor for the HVAC or the heat pump
2. The electric oven
3. Electric ranges
4. microwaves
5. Electric clothes dryers
6. server rooms for electronic equipment (computers can draw a lot over time)
7. Plugs for the home office (computer)
8. Electric hot water heater, ESPECIALLY on demand ones.
Ect. You should definitely OVERSIZE the wires for some of these circuits, as we can see from the calculation above. Definitely the one for the heat pump, since that is a big draw. Possibly one size up from what you need for some of the other circuits.

Remember, wiring codes are based upon SAFETY, not efficiency. The power lost in a smaller wire is HEAT, and too large a load on a wire causes it to melt or start a fire. So, wire gauge standards are chosen to allow, say, a 10 amp circuit to work safely all the time without melting, with plenty of safety margin. But, that wire could easily be wasting energy all the time.

If you don't believe me, here's a simple example : if you have a shop vac, an electric iron, or a Foreman electric grill, run the appliance and feel the cord afterwards. It's HOT, isn't it?

Let me try to simplify this. When current is pulled through a wire, it causes a voltage drop which is based on the resistance of the wire. The bigger the wire, the less resistance. If your AC voltage at the box is 120 V rms, and you drop 7 V rms in the line, only (120-7)/120=94.16% of the electicity you bought has made it to the appliance. For example, your light bulb is now only putting out 6% less light as it would have put out if it was right on the box, but it costs you the same amount to run. In the case of a regulated power supply, like on a stereo, it will compensate and pull even more power though the line, costing you even more.

Is it worth it to oversize the lines? I have seen stores selling #14-2 for the same price as #12-2. In a situation like this, you should always buy the better line. If it is going to cost a lot more, I wouldn't unless you will be constantly pulling a lot of power though the circuit. However, since usually you but this wire by the spool, if you have half of a spool of #10 left over, you should definitely substitute it in your higher power circuits, like the kitchen or shop. You can also run multiple runs of wire in parallel, which also reduces the resistance of the wires. But as for putting a lot of money into oversized wires throughout your house, you can probably get a better return investing in solar , wind, or even just putting the money into a CD and collecting interest.

Correct, aadvarcus. It's actually pretty easy to calculate the money saved by a particular wire versus the additional cost.

Say it costs $10 more for a fatter wire to your heatpump compressor. In that case, you calcualate the kilowatt hours/year you expect the heatpump to use, and calculate the voltage drop for the wiring. You then can calculate how many extra kilowatt hours you lose each year. Then, you calculate opportunity cost : you need to save about 5% of the price of the thicker wire each year for the thicker wire to be worth it.

Trivial math, and if you work it out, you'll arrive at a 'formula' for any situation.