Change 240 to 480 to save money?

[Power Tech]

How many have heard this? I have heard this from some good electricians. I know we are charged by the watt not amp. Can there possibly be any truth to it?

 

[jeremysterling]

The savings is not in the amount of power consumed by utilization equipment. The savings is in the size of the gear and conductors used to get the power to the utilization equipment.

 

[brian john]

And if you have to step up to achieve 480 it will cost more besides the equipment there is the efficiency issue while minor it exists.

Depending on the situation there may be times where VD may play into this equation and utilizing 480 makes sense.

 

[LarryFine]

The theory is that insulation is cheaper than conductor, plus voltage drop is current-dependent. Two ways to save.

 

[Power Tech]

The theory is that insulation is cheaper than conductor, plus voltage drop is current-dependent. Two ways to save.

I should have spent more time explaining the situation I encountered.

I went to a small machine shop on a call. The electrical contractor there was in the process of changing the voltage to his equipment to 480 from 240 because --- his bill would be cut in half.

I told him to have them reconnect everything, and call me after they are gone. The do not know what they are doing. They are selling you snake oil. He says "but the machines will pull half the amps. I said "that's great except we are charged by watts, the PoCo's figured that out a long time ago".

 

[growler]

Give me a break, the customer calls me out and pays me for a service call.

You are correct, if a customer pays for a service call then it's your responsibility to give the best service possible and that includes telling the customer the truth.

In the medical or legal professions this would be known as getting a second opinion and even there it's considered OK to tell the customer the truth to the best of your abilities. I was once told I needed a back operation and the second doctor I went to told me no way should you ever let anyone operate on your back unless it's absolutely necessary.

 

[brian john]

This has been an on going discussion in the DIY, home wood worker community, fortunately there are a wealth of electricians and engineers working to dispel this myth.

Even though I know some electricians that buy into this and offer to convert motors from 120 to 240 for the savings

 

[growler]

Even though I know some electricians that buy into this and offer to convert motors from 120 to 240 for the savings

If it's a 120/240V motor and there is space available then I always tap the motor for 240V. Everything should run a little cooler and there should be less voltage drop, which is better for motor operation over time.

I do think there are advantages of 240V over 120V but some people just get confused about what those advantages are.

 

[don_resqcapt19]

If it's a 120/240V motor and there is space available then I always tap the motor for 240V. Everything should run a little cooler and there should be less voltage drop, which is better for motor operation over time.

I don't see how the motor runs any cooler on one voltage than on the other. The windings each see exactly the same current and voltage no matter if they are connected for high or low voltage operation.

 

[augie47]

I don't see how the motor runs any cooler on one voltage than on the other. The windings each see exactly the same current and voltage no matter if they are connected for high or low voltage operation.

I guess this also means you are not interested in purchasing my "super savings power cube" guaranteed to cut your electric cost by 25% :grin:

 

[Rewire]

Tapping your motors at 480v allows you to have nore motors connected to your loadcenter.it also allows you to have a larger horsepower motor on a smaller branch circuit.The only cost savings you will see is at installation.

 

[LarryFine]

If it's a 120/240V motor and there is space available then I always tap the motor for 240V. Everything should run a little cooler and there should be less voltage drop, which is better for motor operation over time.

I do think there are advantages of 240V over 120V but some people just get confused about what those advantages are.

Agreed.

I don't see how the motor runs any cooler on one voltage than on the other. The windings each see exactly the same current and voltage no matter if they are connected for high or low voltage operation.

The motor itself, no, but the system, yes. Of course, a properly-designed system or circuit will be sized for proper operation, but that might include larger conductors.

The perspective of this idea is that, for example, with a motor small enough to be supplied by #12 conductors either way, there will be less conductor heat at the higher voltage.

 

[Mr. Bill]

I got into this arguement with an Engineer at another firm a couple weeks ago. Doing a renovation of some motors at a faciluty. Removing some motors, replacing others. Total load decrease. Insisted on changing the service from 240V to 480V for the energy savings. Claimed a 2.5 year payback. The architect said it sounded weird and word got back to me. Not my project but I knew the architect and I advised him that kVA*hours = kVA*hours regardless of voltage. He showed my response to the engineer who still insisted there would be significant savings. He said the starting current was significantly lower and that this would reduce the peak load charge from the utility. I said again the Utility doesn't charge for amps. The starting kVA would be the same regardless of the voltage. Didn't push it any further since it wasn't my client. I would love to know where he got the 2.5 year payback number.

I see a very small savings from voltage drop by using 480V. About 0.38% for a large motor at 100' away. Which is usually offset by transformer losses steping down to 120V for receptacle loads in the building. Depends on the building I know but as a generic rule of thumb I see energy use as equal. Fractional percentage one way or the other doesn't bother me. I do see cost savings on new construction since the higher voltage means small gear and wire. But that's not the same as energy savings. And really not on a renovation job like this unless I needed to change the main gear for some other reason.

 

[StephenSDH]

I don't see how the motor runs any cooler on one voltage than on the other. The windings each see exactly the same current and voltage no matter if they are connected for high or low voltage operation.

If you have more voltage drop due to 120 then your motor will lag more drawing more current creating more voltage drop. Thats why you can burn up your tools using a long cheap extension cord. If the motor doesn't have enough voltage to generate torque when loaded then it lags/stalls.

 

[petersonra]

Sometimes it is much cheaper to get a 208V service than a 480V one. It sure is around here.

A fair number of plants are fed with 208 and have their own transformers to bring it up to 480. never could understand the thinking.

the place I used to work had a set of 208 to 480 transformers in a vault outside that had to be a good 6 feet high and maybe 4 feet in diameter and were loaded to the gills. ironically they were leased from the poco. why the 208 service was so cheap that it was cost effective to lease transformers to make 480 for the building is beyond my pay grade.

 

[brian john]

I run all my woodworking equipment that an be run on 240 at 240, but, that is because I can....Heck I ran #10 to all the motors so VD should not be a problem?

 

[don_resqcapt19]

If you have more voltage drop due to 120 then your motor will lag more drawing more current creating more voltage drop. Thats why you can burn up your tools using a long cheap extension cord. If the motor doesn't have enough voltage to generate torque when loaded then it lags/stalls.

If the voltage drop is excessive on the 120 volt circuit the installer did not use a large enough conductor.

 

[LarryFine]

If the voltage drop is excessive on the 120 volt circuit the installer did not use a large enough conductor.

The come-back to that is that smaller conductors can be used for a given kva (obviously.)

In a manner of speaking, it's the heat from voltage drop that requires the larger conductors.