ON topic 3phase ?

My shop is on our property. We currently have single phase 240V, but are switching over to 3-phase. I have 2 choices. I can either go with

240V 3-phase. Or get them to do 208V 3-phase. This feeds our House, well pump (20 years old now) and my shop. We have 2 meters (shop & house)

Question is. I would prefer to go with 208V, then I don't need a

240V-208V buck transformer. (I don't have one now, but that is another story) But, accord to the electric company guy, most people don't like 208V as the 220V devices, stove, Air conditioner, etc don't work as well. stove takes longer to heat etc..........??

Also it means slightly higher current draw. What I am most concerned about is the well pump. I am surprised it has lasted this long, and not looking forward to replacing it. Higher current/lower voltage means shorter motor life, right? Heat kills motors.

Anyone have any experience with 208V vs 240V, that justifies getting a buck transformer? They are not cheap, for a silly 20% step down box-heater.


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Why not keep the house 120/240 single phase and just put the three phase to the shop? or is this what you're doing? Thinking here, (ouch! ) If the power Co. hangs 208 xformers they will not leave the

240 volt for the house there...correct? Then you are stuck with 208 for everything.

I'd go with the 240 Volt, residential stuff is not made for 208, and the lower voltage will most likely end up costing you more in power usage.

I'm running a 240V open delta here and everything works great even my CNC verical mill thats marked 220Volt.

What do you have that's 208 and do you really need a step down xformer for it?

Thank You, Randy

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Clay, Just go the cheapest route, 120/240 open Delta. Your motors will be happy and so will your house. The power company will be happy because it only takes two transformers, one will be center tapped, the other will supply the third leg. 120/208 is popular because it balances the load, for the power company, not for you. However you mostly find it in industrial plants as a secondary voltage to 480/277. There it is used to feed all the 120 volt stuff and you can balance the loads properly. If you have three phase you'd be crazy to run anything on 208 single phase, so you almost never have any of those loads.

Gary H. Lucas

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Gary H. Lucas

I cook-a-fried a 3phase power supply AND DC servo drive on my Mill last week. Popped a small 2A mainboard fuse in the Lathe a few weeks earlier.

Had a DC servo fail spectacularly & rebuilt 4 months ago, may have blown a AC snubber cap in the DC power supply then, that caused a slow chain reaction, that resulted in the Power supply/servo failure last week. Checked voltages from the rotary phase converter. 250V, wild leg 260V.

240V line voltage. (see my other post about power supply electronics)

According to two service techs my machines are designed to run on 208V NOT 240V. This is the first I have heard this, so it would be nice to know what the real deal is there. (the snubber caps are rated 250V AC. They have been running at 250V-260V for five years. Over voltage is what blows caps. I am currently paranoid about turning the machines on again, until I have this power issue resolved.

I don't think I can have 2 separate lines to the property. Buck transformer would only be on the shop. Just wanted to know if the one time cost of a buck transformer was worth the headache of long term 208V

3-phase issues. My wife is not thrilled about having her oven on 208V. She bakes everyday.

I think the power company will put whatever I ask for on the pole, I just know what to ask for.


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