Power loss in conductors

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Hello

If we upgrade service from 120/277 3 phase, 4 wire to 480/277 3 phase wire, size of conductors get smaller. My boss says to me that the utility bill will go low as well because of I2R losses in the conductors.

As Size of conductor is smaller, its resistance is small, which leads to lower losses.

I don't think it going to make any impact. It makes impact in transmission lines because of long distance.
Resistance is directly proportional to length and square inversely proportional to area.

I dont think its large area difference between #10 & #6 wire.

Please help
 

Cold Fusion

Senior Member
Location
way north
Hello

If we upgrade service from 120/277 3 phase, 4 wire to 480/277 3 phase wire, size of conductors get smaller. My boss says to me that the utility bill will go low as well because of I2R losses in the conductors.

As Size of conductor is smaller, its resistance is small, which leads to lower losses.

I don't think it going to make any impact. It makes impact in transmission lines because of long distance.
Resistance is directly proportional to length and square inversely proportional to area.

I dont think its large area difference between #10 & #6 wire.

Please help
I'm not clear on what you are contemplating. Your explanation doesn't make sense.

The existing is 208/120, 3hp, 4Wire, #6?

The new service will be 480/277, 3ph, 4Wire, #10?

"Service" usually means the connection to a utility. I don't think I have ever seen a 3ph, commercial or industrial service that was #6 or #10.

It sounds as though this is a change to an existing facility to save dollars on the electric bill - if so, then there is a whole bunch of stuff to consider. Hee are a few:

1. Transformer 480/208V for existing loads that are not easy to change to 480V. Don't forget the losses through this transformer

2. New 480V motors unless the motors are rated for 480V. MCC rated for 480V, cause the wxisting are 208V.

3. New 277 lighting?

If this is a new installation or major addition - that is an entirely different animal with different economics.

cf
 

nakulak

Senior Member
did you mean 208/Y120 ?

do your boss a favor. get the last 12 or 24 months worth of bills. save the next 24 and post the results for us and him. I will be interested in the results.
 

steve66

Senior Member
Hello

If we upgrade service from 120/277 3 phase, 4 wire to 480/277 3 phase wire, size of conductors get smaller. My boss says to me that the utility bill will go low as well because of I2R losses in the conductors.

As Size of conductor is smaller, its resistance is small, which leads to lower losses.

I don't think it going to make any impact. It makes impact in transmission lines because of long distance.
Resistance is directly proportional to length and square inversely proportional to area.

I dont think its large area difference between #10 & #6 wire.

Please help
You have it backwards: the possible savings are because the current is lower, not because the wire is smaller. The smaller wire actually increases the I2R losses.

Anyhow, I think you are right. In most places there wouldn't be a large difference in the I2R losses. More savings come from the fact that smaller wire costs less.

Steve
 

StephenSDH

Senior Member
Location
Allentown, PA
If you are like most plants, any savings will be well washed away by the cost of replacing equipment. Your I^2R losses will likely still be the same if you reduce the wire size for 480v. If you have to backfeed old 208/120 equipment then you have the waste of transformers efficiency losses.

If you need to increase your service's KVA anyways it might make sense to take the step.
 

drbond24

Senior Member
As Size of conductor is smaller, its resistance is small, which leads to lower losses.
Smaller wire actually has a higher resistance.

As steve66 said, the potential savings in going with a higher voltage service is in decreasing the current, not in making the wire smaller. You were right that losses on the lines are I^2R. If you can lower 'I', the losses go down fast.

However, in your case, any savings will fall well into the 'negligible' category.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
The way I interpreted it is that you are asking if you take your existing wires, which are sized for 120/208 load ampacity, and step the voltage up to 480/277, will the resultant lowering of current on the existing wires result in a lower energy loss in the overall system?

I think that Cold Fusion was on the right track (with others). There is more to changing voltage in an existing facility than just the lowering of current. Your existing 120/208V system is doing something now, correct? That implies that you have equipment, and that equipment is rated for 120/208V. If you change to a 480/277 supply, all of that equipment will no longer be capable of being connected. So now you will have to either 1) add transformers to step down from 480 to 208V, or from 277 to 120V, or else 2) you will have to buy new equipment rated for 480 and/or 277V. So as has been said, the losses in these new transformers will more than offset any savings from I2R loss reduction, or the cost of new equipment will not be justified by the infinitesimal savings you might realize from lowering the current.

If for some reason you are going to be replacing all of the equipment anyway, say for instance a catastrophic fire and a fat insurance check, then yes, there will be a very small amount of energy savings from the reduced i2R losses.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
In theory, and with the usual all-other-things-being-equal caveat, a properly-sized 208Y/120v system should perform the same as a properly-sized 480Y/277v system.

The only difference would be if one system's power requirements happened to be real close to the selected conductors' ampacity, and the other's had more headroom.

The system with the greater headroom should suffer less IR^2 losses. The favor could be towards either voltage, depending on realistic load calcs and conductor choices.

However, the above posts are correct. The cost of equipment change-out would never be recouped if done solely for the purpose of a voltage change alone.
 

hurk27

Senior Member
I wonder if his boss is thinking like many who don't understand Ohm's law, that because equipment pulls, half of the current at the double of the voltage?

This might be one of those 120 volt verses 240 volt belief's

You don't know how many times I was told by home owners they wanted their air compressor in the garage wired for 240 volts, so it would only cost them half as much to run.
after explaining that we pay for watts not amps and the watts are the same at both voltages, it really surprises most of them as they always say "well that was what I was told by my grandpa, and he was an electrician for 40 years"

This myth is still out there.
 

WDGILBERT

Member
Power loss in conductors

There are at least two advantages to using a higher voltage.
1) Cheaper installation since you can use smaller wire.
2) Less line loss. For instance, if you replace a 120 V, 24 A load with a 240 V, 12 A load for a 100' length of wire, the savings in line loss is as follows:

For 120 V, 24 A the Loss (watts) = 24*24*2*0.124(resistance of 100' of #10wire) = 142.84 watts.

For 240 V, 12 A the Loss (watts) = 12*12*2*0.314(resistance of 100' of #14wire) = 90.43 watts.

The savings is 142.84-90.43=52.42 watts. This may not seem like much since it is only about 3.1% of the total load of about 2880 watts; however, at $0.15/kwh, running 24/7 that comes to about $118.82/yr. Any home owner would be glad to have that money in their pocket. In the industrial world with higher voltages, the savings would add up much faster and could mean the difference between being competitive or not.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
WD, I'd be interested in the same figures using 25a and 50a loads. You'd probably use #10 and #8 wire.
 
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