240V delta 3ph service: does running 240 single phase using high leg save money?

cosmos_275 · Jun 25, 2018

I have 240 delta in my shop, so they read 120-120-208. The electrician who ran the 3 phase told me if I use 240 single phase breakers to use half of it on the high leg. He said this would save me money. I didn't get any explanation. Can anyone explain how this could be true? The only thing I can think is they don't meter that leg.

Strostkovy · Jun 26, 2018

I don't see how you get 208 anywhere. Shouldn't it be 120-120-240, then have a ~170 or so stinger leg to neutral, but always have 240 between hots?

If you use the stinger lead to feed a panel for 240V breakers (you absolutely cannot have any loads that use neutral on that panel) then you would be better balancing your loads. Also, if you are maxing out two legs at your service amperage, you can redistribute loads onto the third leg and get a bit more juice out of your service.

9100 · Jun 26, 2018

Look up high leg, sometimes incorrectly referred to as "wild leg". It isn't wild, just referenced to a ground in the middle of the base leg. These services are common in farming areas where customers have some three phase equipment. The three legs of a delta service are brought in and the ground is on the center tap of the base That allows the use of 120 V on each side of common, 240 single phase across the base and 240 three phase with only one transformer and four wires. 208 is what you get calculating the altitude of an equilateral triangle 240 on a side.

OP, see if your meter is single or three phase. I doubt the story because power companies have few charitable impulses.

Bill

Strostkovy · Jun 26, 2018

9100 said:
Look up high leg, sometimes incorrectly referred to as "wild leg". It isn't wild, just referenced to a ground in the middle of the base leg. These services are common in farming areas where customers have some three phase equipment. The three legs of a delta service are brought in and the ground is on the center tap of the base That allows the use of 120 V on each side of common, 240 single phase across the base and 240 three phase with only one transformer and four wires. 208 is what you get calculating the altitude of an equilateral triangle 240 on a side.

OP, see if your meter is single or three phase. I doubt the story because power companies have few charitable impulses.

Bill

I understand now. Way different than what I was thinking.

Good to know my RPC makes 208 single phase too though.

cosmos_275 · Jun 26, 2018

9100 said:
see if your meter is single or three phase. I doubt the story because power companies have few charitable impulses.

Bill

It appears to be three phase as it says "Va Vb Vc" so I guess no free lunch. He must have been trying to make up for wiring the overhead lights to the 208. Fortunately only a couple bulbs suffered.

Thanks

jonok · Jun 26, 2018

I know that some mechanical meters don't reference anything relative to neutral, and just assume a balanced load. If you're using a lot of 240 single phase, and don't use the wild leg, it stands to reason that you're shooting yourself in the foot. Now if you have 240 singe phase equipment that has a neutral so that you can run 120 for stuff like lights and timers, you're sort of stuck.

I rather suspect with the advent of electronic meters, they know exactly how much you're using, and how to maximize the bill...

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