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miked56
Registered Users
Posts:78
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| 11/17/2006 6:07 PM |
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| 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 |
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TIA -- Mike |
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gdeno
Registered Users
Posts:1
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| 11/20/2006 1:56 AM |
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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. |
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John Rahm
Registered Users
Posts:1
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| 01/23/2007 1:19 AM |
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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. |
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bonzai95
Registered Users
Posts:18
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| 02/15/2007 10:35 AM |
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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
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Jamie
Forum Moderators
Posts:1480
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| 02/15/2007 6:22 PM |
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This message is from Steve at the CR4 site. (Thanks Steve!)
Consider a 20 Amp circuit with a 100 ft run of cable and that's under a constant 10 Amp load (that's high). You'd normally use #12 Romex cable for this run, but could upsize to #10 Romex.
Some specs we'll need:
#12-2 AWG Romex cable:
Resistivity: 1.558 Ω/1000 ft = 1.588 mΩ / ft.
source: http://en.wikipedia.org/wiki/American_wire_gauge
Cost (250+ ft): $0.82/ft
source: http://www.azpartsmaster.com/shopazp/Wire+%2D+Electrical.html
#10-2 AWG Romex cable:
Resistivity: 0.999 Ω/1000 ft = 0.999 mΩ/ft.
Cost (250+ ft): $1.33/ft
Losses
At 10Amps load, our losses are:
#12 Wire: 102 * 0.001588 Ω/ft * 100 ft = 15.9 Watts
#10 Wire: 102 * 0.000998 Ω/ft * 100 ft = 9.99 Watts
So we'd save: 15.9 - 9.99 = 5.91 Watts
Over an 8760 hour year, that's 51.8 kWH
At 10 cents/kWh, that energy costs: $5.18
Cost difference:
($1.33 - $0.82) * 100 = $51 to upsize the wire.
So your payback time is pretty much exactly 10 years, which doesn't seem like a great investment to me. In reality, the loading on the circuit is probably much lower so the losses will be lower and the payback time will be even longer. |
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vermaraj
Registered Users
Posts:34
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| 02/15/2007 8:19 PM |
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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.
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Cameron
Registered Users
Posts:2
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| 03/07/2007 2:29 AM |
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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.
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Cameron
Registered Users
Posts:2
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| 03/07/2007 2:36 AM |
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The skin effect at 60Hz limits the current to the outer ~8.5mm, that's about 1/3 of an inch.
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miked56
Registered Users
Posts:78
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| 03/07/2007 4:35 PM |
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Posted By Cameron on 03/07/2007 2:29 AM
Power lost along the line is wasted. Reducing the line resistance will reduce wasted power.
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? |
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TIA -- Mike |
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gadero
Registered Users
Posts:1
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| 03/26/2007 5:45 PM |
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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? |
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CH66
Registered Users
Posts:1
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| 07/01/2008 9:08 AM |
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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.
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Brock
Registered Users
Posts:203
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| 07/01/2008 12:24 PM |
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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. |
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Green Bay, WI. - geothermal heated indoor pool with a small solar setup |
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