voltage loss in conductors

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plt

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I read an article about how uping the size of the conductors in a circuit over the period of one year resulted in quite a bit of savings as apposed to an identicle circuit sized correctly.
While discussing this issue a question arose. If the service drop on the utility side is undersized would this have an effect on the overall efficiency of the system beyond the meter since it was already dropping voltage and causeing the system as a whole to pull more amperage to maintain wattage? I say that it would not affect it in that we are talking about efficiency from the meter to the loads. not on the system ahead of the meter and all we were trying to do is to slow the meter as much as possible to the same loads waying cost of wire and termination methods. One wire size up theoretically losses 25% less wattage over a one year period assuming an 8 hour run everyday on a 20 amp circuit over a 50' load center length. Am I wrong or can anyone lead me to more info that would help convence this friend? either way would like to know.

Just an experiment with theory.
Thanks
 
Re: voltage loss in conductors

PLT, work some numbers. For example use a pure resistive, say 8 ohm's @ 120 volts. Then work out the power on say a superconductor 0 ohms, then start adding resistance for wiring. Look and see what happens total power consumed at the load and wiring.
 
Re: voltage loss in conductors

Plt
If you have a 50 ft circuit of #12 with the max load of 16 amps the watts loss is
16x16 amps x (2.0 ohms/1000 ft x 50 ft)/1000 x 8hrs = about 204 watt hrs or 0.204 kwh per day.
That not much of a loss. You may get a 25% decrease by increasing the wire size but 25% of a small number is a small number.
If you want to decrease energy use check out the type of lighting your are using and try to reduce the demand charge if there is one. Power factor improvement may mean a large savings.

Corrected caculations for I?

[ November 14, 2004, 04:59 PM: Message edited by: bob ]
 
Re: voltage loss in conductors

I agree with Bob's premise that you won't save enough money to make larger wire worthwile in most cases, I'm not so sure about the calculation.

Watts = current squared x resistance

Also there is power loss in the neutral of a single 120 volt circuit so the distance should be 50'x2

(16x16)x(2/1000)x50x2 = 51.2 watts lost
51.2x8/1000 = .41 kwh per day

Here in southern New Mexico that is worth 3 to 5 cents a day. But, you should realize that very few 20 amp 120 volt circuits have 16 amps on them for 8 hours. A more realistic average would be less than 4 amps.

Given that the power loss varies with the square of the current, 4 amps continuous current would offer 1/16 of the loss that 16 amps would. Now we are back to really insignificant.

Jim
 
Re: voltage loss in conductors

Take a look at the organization that is putting out the information and consider: </font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">the assumed load on the circuits</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">the duration of the load on the circuits</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">the assumed cost per kWh</font>
<font size="2" face="Verdana, Helvetica, sans-serif">If this is a residence, I assure you that you will never meet those parameters. If this is a commercial store, the lighting circuits may if the cost per kWh is that high. if this is an industrial plant, they will have some circuits that this may apply to but the cost per kWh will probably be lower than that due to the local tariff and the rate they are on.

The bottom line is that there are a lot of assumptions that may or may not hold up. It certainly can't be applied everywhere. :D
 
Re: voltage loss in conductors

Originally posted by charlie:
Take a look at the organization that is putting out the information and consider: </font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">the assumed load on the circuits</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">the duration of the load on the circuits</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">the assumed cost per kWh</font>
<font size="2" face="Verdana, Helvetica, sans-serif">
Click to expand...
The copper people would not lie to us would they? :D

Another point I would make is that if the loads are straight up restive loads the "lost voltage" will mean the loads draw less power.

So the lamps may be a little dimmer but the total power used will be the same.
 
Re: voltage loss in conductors

Dear iwire

Amps and volts have a direct relationship in a resistive circuit, you are correct. Drop the voltage by 10% you will drop the amps by 10%. But the relationship betwee volts or amps and watts is a squared relationship. If the voltage or current drops from 100% to 90%, the watts drop from 100% to 81%.
watts = current squared x resistance or
watts = volts squared/resistance
 
Re: voltage loss in conductors

I checked their calcs, conduit fills and voltage drops. All of the examples are fully loaded circuits, lots of hours per year, and marginally acceptable voltage drop (long circuits). And they are right - heavily loaded, long, continuously operated, industrial/heavy commercial grade circuits benifit from upsizing the wire from code minimums. That's not news, that's called good design.

carl
 
Re: voltage loss in conductors

I like (meaning I really don't like) the way they say "installing wire ONLY one size larger saves".

I wonder how many people assume they can save more if they install wire 2 or 3 sizes larger.

I agree that this only makes sense for wires that have marginal to high voltage drop, and are in use a lot of the time.

I also doubt that the power produced by wiring is a major factor in the HVAC equipment load.

Steve
 
Re: voltage loss in conductors

Originally posted by jtester:
Dear iwire

Amps and volts have a direct relationship in a resistive circuit, you are correct. Drop the voltage by 10% you will drop the amps by 10%. But the relationship betwee volts or amps and watts is a squared relationship. If the voltage or current drops from 100% to 90%, the watts drop from 100% to 81%.
watts = current squared x resistance or
watts = volts squared/resistance
Click to expand...
And your point is?
 
Re: voltage loss in conductors

IMO, it would only be worth it to upsize the wires if the customer was expecting a sizeable load increase in the near future. In most applications, not going to save you much on the electric bill.
 
Re: voltage loss in conductors

Dear iwire

I may have misunderstood your message, you said that the lamps may be a little dimmer but the power will be the same.

My thought was that the power drops off at a much faster rate than either the voltage or the current.
 
Re: voltage loss in conductors

Power at the load will drop off faster. But the power of the intire circuit at the point the circuit recives it's power won't. this will include the power lost in the wire. which will add back to the total wattage the circuit uses.
 
Re: voltage loss in conductors

thanks for the posts and ideas. the main idea was to use less to get the same without uping the implimination costs beyond reason. mainly for power conservation. especially some of the high rise structures we deal with at work but it would be a fun experiment to try even at home. MY HOME OF COURSE. I couldn't do that with some one elses. The problem with the hypothosis is that some beleive that by putting a smaller service drop in and there by increasing voltage loss the equipment would be working harder anyway and if that is the case why try at our level. REALLY GOOD INFORMATION. thanks again.I will be going over these posts for a couple of days and plug in the numbers. OUTSTANDING. thanks
 
Re: voltage loss in conductors

good engineering dictates upsizing for long runs anyways for voltage drop.
About the only way it makes sense is for something insignificant first cost like going from a #12 to #10, when the conduit is already large enough that you have no change there. The labor rate is the same for both and if you are feeding lighting fixtures which are on for many hours a day then it could make sense. But you really have to do the calc for every situation to see if it is beneficial economically.
It is like the EE WHIZ license plate i see driving down the interstate for his hybrid car. Those financially don't make sense even for a long commute like mine. The upcharge to go from a conventional gas engine car that can get over 40 mpg to some hybrid that gets a little over 50 mpg takes more than 8 years to pay back. Assuming that maintenance is not outrageous on the hybrid, since they are oddballs. So I guess that EE WHIZ did not take engineering economics, or he just is a environmentally concerned person who thinks the little bit of pollution saved is better than the land fill worth of batteries it will create.
Sorry, got a little off topic.
 
Re: voltage loss in conductors

Hybrid cars really make no economic sense for hghway driving at all. They only make economic sense for those who do a lot of stop and go driving. For highway driving the increase in gas mileage over a conventional similar vehicle is not signigificant despite the EPA ratings.

OTOH, they have the "cool" factor going for them, which ought to sell a fair number of them on its own.
 
Re: voltage loss in conductors

Jschultz, I believe the car batteries used in hybrids are recyclable. Some car manufacturers even offer a couple hundred bucks for each one. I'm not sure how much is re-used, but you're right it will probably still create more waste eventually.
 
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