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Thread: Any issues running 3-phase 208v power rather than 230v or 460v?

  1. #1
    MetalCarnage's Avatar
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    Default Any issues running 3-phase 208v power rather than 230v or 460v?

    I am in the process of getting my little shop set up for a mill I picked up. Currently the motors are wired for 460v 3-phase but they can be re-wired for 208-230. Here is one of the motor tags:



    To make a long story short, the easiest and quickest way to get 3-phase out in my shop was to put in a 4-wire, 100amp service at 208v. Now, I know the motor tag references the 208 in the "lo volts" column but what I am wondering, is there any reason I would want to bring in a transformer and convert the 208v input to 230v or 460v? Would the motor be more efficient, have more torque, or just plain run smoother?

    I have an electronics background but power systems and 3-phase were not included in my sphere of expertise.

    Thanks much,

    -Ron

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    Shawn Ghormley is offline Stainless
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    Are you sure your service is 208V?

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    TDegenhart is offline Titanium
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    That 208/230 is a compromise. In order to obtain U/L listing the motor has to meet temperature requirements at 253 volts, +10% of max rating. To meet NEMA standards, the motor has to function at 85% of 208. For magnetic devices that is almost impossible so often the low end suffers.

    Tom
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    S_W_Bausch is offline Diamond
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    Quote Originally Posted by TDegenhart View Post
    That 208/230 is a compromise. In order to obtain U/L listing the motor has to meet temperature requirements at 253 volts, +10% of max rating. To meet NEMA standards, the motor has to function at 85% of 208. For magnetic devices that is almost impossible so often the low end suffers.

    Tom

    Tom will know better than me, but I suspect that 208 3 phase was created as a "one panel fits all" standard. A qualified electrician can acquire 120 volts single phase, 240 volts single phase, or 208 volts three phase.

    Of course, anyone with a voltmeter could figure it out, but it never hurts to know more, rather than less.

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    Modelman is offline Stainless
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    Pray tell, how does one get 240V single phase out of a 120/208V "Y" service? Lots of stuff is 240V single phase... home shop size table saws, buzz-box welders, clothes driers and large air conditioners to name a few, and most are NOT rated to run on 208V. I wouldn't consider putting in a 208V service unless that was all I could get

    Everybody seems to get all worked up over the 240V "high leg delta" services. Why? From one, you can get 240 3ph.,, 240 single ph., and 120V lighting and outlet circuits from the same panel. Only issue is you lose 1/3 of the breaker slots for 120V use... So, buy a bigger panel. Or use a two pole breaker to feed a single phase sub panel for the lighting.

    Hint... most panel manufacturers sell blank covers to fill the unused slots if you break out the wrong knok-out tabs, or make changes that require leaving slots open.

    Dennis

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    Quote Originally Posted by Shawn Ghormley View Post
    Are you sure your service is 208V?
    According to my DMM, yes.

    Quote Originally Posted by TDegenhart View Post
    That 208/230 is a compromise. In order to obtain U/L listing the motor has to meet temperature requirements at 253 volts, +10% of max rating. To meet NEMA standards, the motor has to function at 85% of 208. For magnetic devices that is almost impossible so often the low end suffers.

    Tom
    Okay, that tells me I should do "something" but I could use some help as to "what".

    Thank you.

    Okay guys, like I said, I don't know power systems but I have done a bit of reading on 3-phase and the "high leg" setups. I still don't have a firm grasp and the results of my measurements don't quite jive with my understanding of it (flawed as it may be).

    I have four wires, black, red, blue (high leg), and white (ground). The voltage I get reading from both black and red to ground is 120v while blue to ground is 120.5v. When I read from black to red I get 206.8v and reading from both of those to the blue produces 208v & 208.4v respectively. The measurements were taken with a FLUKE 87 III True RMS multimeter.

    Now, what is the best way to set this up to power my mill or what can one do to make it closer to optimal?

    Thanks again guys,

    -Ron

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    Modelman is offline Stainless
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    That's not a "high leg" service. On a high leg service, all there "legs", L1, L2, and L3, typically black, blue, and red, will read 240 +/-10% between each other, two of the lines will read 120V to ground, and the third line will read something like 184V to ground, and is unusable for anything. The reason is the common is derived from a center tap in one of the transformers, and that is what is bonded to ground.

    What you describe is the classic 120/208 Y service. You can use any of the three line and the common for lighting circuits, but you can't get 240V single phase.

    If that's what you have, that's what you use. The motor in your mill IS rated for 208V, so it should be OK. You will have to check the taps on any control transformers present to make sure they are wired for 208V, and you have to use the amperage listed for the 208V when sizing fuses or motor overloads.

    If you need 240V single phase for something else, that's when you start looking for the appropriate sized boost transformer.

    Dennis
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    Okay, that makes a lot of sense now.

    Thanks much Dennis,

    -Ron

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    TDegenhart is offline Titanium
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    First thing is the op didn't say anything about single phase. He said the easiest and quickest way was to bring 208 4 wire which he did. His question is would a motor rated 208/230 be ok or should he up the voltage with a transformer to 230. The answer is the motor will work but there are compromises. If you look at the nameplate, the 208 current is higher than the 230. Now normally, one would expect the current at the lower voltage to be lower. The reason it is higher is in order to supply the same hp, the motor speed is lower. 1740 rpm is approximate. It varies with load and that is what is happening here. Also note that the service factor is 1.0. That means there is no built in overload capacity.

    The end result is that the motor will work, will produce 3hp, but will run hotter and slower. How much hotter I don't know.

    Should a transformer be installed to up the voltage? The only comment I have for that is that most industrial electricals and electronics are 230/460 or 240/480. If this is a one time thing then it is cheaper just to leave things alone. But if there is additional equipment in the future then I would install a transformer.

    Tom
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    Thanks Tom. I'm not sure if it will be a "one time thing" or not. Right now I have a mix of equipment - mill is 3-phase, lathe is single phase 110v (that could easily change as the motor needs work/replacing), both my welders as well as the shaper are single phase 220v, everything else that runs off this panel is single phase either 110v or 220v (drill press, bandsaw, lights, HVAC, garage doors, etc.) What the future will bring in the way of equipment is anybody's guess.

    To give a bit of background and as to why I have what I have - My "shop" is set up in a small garage for my office building. I had this stall leased out to a communications company for a time where they kept some equipment to run a cell "repeater station"/booster or whatever you call it these days. For their equipment I provided 220v and an HVAC system. Once they went belly up or were bought out I was left with a garage that you couldn't park in but had heat/air, perfect for a personal "shop". The power to the garages was supplied through a 1.5" pvc pipe that went under the parking lot and into my building's equipment room. As only single phase was required only two (#3 awg for 100amp service) of the three legs were pulled through. To get 3-phase out to the shop I pulled through the third leg. I just got a 3-phase load center via the big brown truck today that I am going to replace the single phase box with and I'll have the same power service that is available to my office building (but only 100 amps). Cost-wise I just had to pay for 200' of #3 awg, the load center, and some breakers. Not the cheapest solution but may be the most reliable I could do with what I have.

    Thanks again,

    -Ron

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    Modelman is offline Stainless
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    So you don't really have 220V single phase, you have 208V single phase. While I agree with all Tom said about 208V 3 phase being less desirable, the motor on your mill IS rated for 208V, and in the context of a hobbyist shop, should be fine. Likely not so with all the single phase equipment, though. That's seriously low voltage for modern equipment designed for 240V, might not be so bad for older equipment designed for 220V.

    You can try it all, and only worry about anything that runs abnormally hot: small single phase boost transformers installed down stream of the branch circuit breaker are going to be a lot cheaper than trying to boost the whole three phase panel to 240V, which would screw up the line to neutral voltage of the lighting circuits.

    I knew there was a reason why they used to make 135V light bulbs!

    Dennis

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    You bring up another question. Just when did things go from 220v to 240v? Everything I have is rated for 220v and some of it isn't THAT old.

    Thanks Dennis,

    -Ron

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    This is just hearsay, but I have been told that the power companies wanted to raise their rates but the regulators wouldn't allow it so they just turned up the voltage a bit to make customers use more electricity. Repeating over years caused the voltage creep. BTW, 208 V motors are available. They work just as well as 240 V motors on their rated power.

    I have worked in two factories with 120/208 services. Both had a lot of older 220-240V equipment. You could cook steaks on the molding machine motors. They ran over current for three shifts from Monday morning to Friday night. The only good thing I can say for 120/208 V is that it saves he builder the cost of a single phase service and gives him time to get out of town before the buyer realizes he has been had.

    Bill
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    TDegenhart is offline Titanium
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    To answer the first question, when did 220 become 240. That happen in 1966. NEMA changed the voltage standards from 110/220/440/550 to 115/120, 230/240, 460/480 and 575/600. The first value is the utilization voltage, the second the source voltage. The difference is the account for line drop from the transformer to the end use. As Bill as stated, the voltages have creeping up to allow the power company to deliver more energy without new lines. A general comment about motor overcurrent and temperature is of little or no value. What is affected is the insulation life of the motor. For every 10 Celsius increase in temperature, the insulation life is halved. Those molding machine motors may have been designed with the extra temperature capacity or the owners may have said "run um til they fail, then replace them".

    Don't quote me on this, but I think 200/208 was or still is a standard distribution voltage.

    Tom

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    Interesting. I may have to pack it in for the day as I've actually learned something. My office building contains 30+ 3-phase motors, all 208v, for the heat pumps and building HVAC loop/tower pumps and is all less than 15 years old whereas my "220v" welders are much less than 10. Thus my questioning of when the "standard" was changed. It would seem that there is a bit more complexity to the story then.

    Thanks again guys,

    -Ron

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    Since the major use of 120/208V services is residential/office buildings where the two main loads are lighting and cooling, I'm sure all the commercial HVAC equipment is available designed specifically for 208V. Same with the maintenance sized welders.

    Of course, if the welders are Chinese... they just mark them however they want.

    Dennis
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    Quote Originally Posted by Modelman View Post
    Of course, if the welders are Chinese... they just mark them however they want.

    Dennis
    Since the three phase motors are "cheaper" that makes perfect sense in office buildings, helps keep my repair/maintenance bills down. You're right on the Chicom welders but that's at least one thing I don't have to worry about. The two I currently have are both Millers, a Syncrowave 200 and a little Millermatic "Challenger". I'll have to look in to how they'll be affected by the 208v though.

    -Ron

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