[mdwkailua]

I have recently moved into a shop that has only 3-phase power available. The electrician has split the 3-phase so I am able to run a table saw with a 230v, 13amp, single phase motor. The electrician is adamant that the motor should run, with no issues, on the 208V that the split 3-phase is providing. I am not convinced that this is true. The saw seems to run fine with only a single blade attached, but if a dado blade is used, the saw will not start. It turns slowly at startup and then trips the 20amp breaker. I am guessing that this is because of the extra mass of the dado set as compaired to a single blade. The motor is also getting very warm after running. I don't beleive the extention cord is part of the problem; it is 12 guage and 25' long.

Right now, getting single phase is not an option and I really don't want to have to buy a new 3-phase motor. My question to all you wise folks out there is: Can a 230V single phase motor run, happily, on split 3-phase at 208V's?

As a added note, the electrician believes that the problem is the motor itself

 

[kennzz05]

It should but when its running close to its maximum load as youve seen problems arise to be sure theyreshould be a rating plate on the motor that states the allowable max and min voltages. Have someone with a meter doublecheck the output voltage sometimes on three phase one leg can have a slightly higher voltage perhaps that will be the case and it can be switched to that leg

 

[InPhase277]

Using two wires of a three phase system is used like you describe is done everyday. I would say a bad capacitor coupled with an extension cord and heavy dado cutter is your culprit.

Most 230 V motors run happily on 208. Get a new start capacitor and a bigger extension cord.

 

[unclduey]

Using two wires of a three phase system is used like you describe is done everyday. I would say a bad capacitor coupled with an extension cord and heavy dado cutter is your culprit.

Most 230 V motors run happily on 208. Get a new start capacitor and a bigger extension cord.

what he said

 

[micromind]

I don't know how many hundreds of 230 volt single and 3 phase motors I've connected to 208 volt systems without problems of any sort.

Generally speaking, a 230 volt motor operated on 208 volts will perform as follows.

1) Full-load current will be about 10% higher.

2) Locked-rotor current will be about 15% lower.

3) Locked-rotor torque will be about 20% lower.

4) Breakdown torque (push a board into a saw until the motor loses speed and almost stalls) will also be about 20% lower.

5) Full-load speed will be about 5% lower.

6) Operating temperature will be about the same, maybe slightly lower.

As stated above, if the motor won't start the saw with a dado blade installed, I'd suspect the start capacitor. Figure around $10-15. Match MFD pretty close, voltage of the new one can be higher, not lower. When you get to it, short the terminals out with a screwdriver before you grab them.

Rob

 

[Yoyizit]

Also, search

dado

on this site. We just had one of these problems.

For such a short length of #12 copper, the contact impedance at each of the two plug/socket interfaces may be more than the 80 milliohms of wire resistance, depending on how much the socket contact spring tension has been reduced over time and the cleanliness of the contact surfaces.
The default fix for this is to clean, and then bolt or wirenut all four extension cord connections.

 

[goose134]

Per usual, I agree with 277. The motor will run on 208, though it is not an optimal condition. Sounds like the capacitor could be getting flaky.

 

[J. V.]

Some/Most motor manufacturers today are name plating at 120/208/240. Some advise not to run on 208 unless the motor nameplate indicates 208. Your motor is proprietary to the saw manufacturer. Try calling them and see what they say about the 208.
The advice above is excellent as usual from the usual people.

 

[Silk]

I have recently moved into a shop that has only 3-phase power available. The electrician has split the 3-phase so I am able to run a table saw with a 230v, 13amp, single phase motor.
Right now, getting single phase is not an option and I really don't want to have to buy a new 3-phase motor. My question to all you wise folks out there is: Can a 230V single phase motor run, happily, on split 3-phase at 208V's?

Why don't you use 2 legs, A and B, A and C, or C and B so you can have single phase 230? If you have a high leg Delta you have all the necessary voltages, you have single phase already.

 

[InPhase277]

Why don't you use 2 legs, A and B, A and C, or C and B so you can have single phase 230? If you have a high leg Delta you have all the necessary voltages, you have single phase already.

:huh:?? That's what the OP is talking about. He has a 208/120 V service. He has used two legs to send single phase 208 to his saw and thinks the lower voltage is causing his problem.

 

[AllanJ]

Most 230 V motors run happily on 208. Get a new start capacitor and a bigger extension cord.

To a 220-240 volt motor, 208 volts is a brownout.

The motor will probably draw more amperes but may work OK. Or maybe it might overheat under heavy load.

For a high leg system with 240 volts phase to phase, any two legs can be used for a "plain" 240 volt single phase circuit. But don't use the high leg together with the neutral.

 

[InPhase277]

To a 220-240 volt motor, 208 volts is a brownout.

The motor will probably draw more amperes but may work OK. Or maybe it might overheat.

Do you see many 230 V motors that aren't rated to run on 208? I don't/haven't. They exist, but most of the motors I have installed have a rating of something like "115, 208/230" or "208/230, 460", or something like that.

 

[Scuba_Dave]

What is the extension cord rated for?
I've seen a lot of 12g cords only rated for 15a
Usually just the plugs causes the 15a rating....

 

[hayewe farm]

There is a slight loss of power and speed because of the phase shift.

 

[mdwkailua]

3-phase/motor answers

I want to thank you all for the insights. I will look into the possible solutions; change capacitor,extension cord, and will certainly talk to Powermatic again. The electrician did meantion that he was surprized to see no frame number on the motor, leading him to think it is a proprietary motor. I'll let you know how things work out.

Thanks again,
Mark

 

[Silk]

:huh:?? That's what the OP is talking about. He has a 208/120 V service. He has used two legs to send single phase 208 to his saw and thinks the lower voltage is causing his problem.

What makes you say that? :huh: In my area there are alot of 240/120 center-tapped Delta systems in the older shops.

 

[InPhase277]

What makes you say that? :huh: In my area there are alot of 240/120 center-tapped Delta systems in the older shops.

Because he said so right in his post. He said he has a 230 V single phase motor connected to two legs of a 208 V three phase system.

I don't think his problem is voltage. I think he has a bad start capacitor.

 

[Silk]

No he didn't, read it again, he said the electrician "split the 3 phase" which doesn't make any sense. Most of the shops in my area have a high leg delta setup so 120 lighting is available and also 240 3 phase for the motors, and also 208. I would not be so sure that the OP's shop isn't wired the same. By the way, I don't think the voltage is the problem either, but I'm also not so sure either him or his electrician know what they are talking about.

 

[InPhase277]

No he didn't, read it again, he said the electrician "split the 3 phase" which doesn't make any sense. Most of the shops in my area have a high leg delta setup so 120 lighting is available and also 240 3 phase for the motors, and also 208. I would not be so sure that the OP's shop isn't wired the same. By the way, I don't think the voltage is the problem either, but I'm also not so sure either him or his electrician know what they are talking about.

The 208 of a delta high leg generally is a by-product and isn't meant to power any loads. But the OP's description of "split 3-phase" I took to mean "two wires of the 3-phase", not "240/120 V delta with a center tapped transformer".

He is a lay person and thus described it as "split". Usually, lay persons are unaware of the 208 V available from a delta system, and so when I hear them mention 208, it is usually in connection with a wye system. At any rate, I'm not saying you are wrong. He could have a 240 V system, but I didn't read that from his post. It reads to me like he has a 208/120 V wye, and his electrician wired his saw as single phase 208 V.

 

[mdwkailua]

Take it easy,now. You'll have to excuse me if I have caused confusion by the wording of my post. I know very little about 3-phase. All I know is what the electrician has told me. He said that the the type of 3-phase I have does not allow for the 240, only 208 and the 120 to power the lights and regular outlets.

Just to add a whole other element here, can the power to my meter be changed to single phase, or is that a big deal?

Mark