208V 2 hots edison tap

[Jeff Ramsey]

I was told an older WW machine that I'm looking at is single phase, "208v with 2 hots and an edison tap". I've not heard that before. Will it run off single phase, 220V that we're all familiar with?

[Rollie Meyers]

220V is a obsolete voltage except in parts of the 50 Hertz world, a 200/208V machine needs a 208V supply, 240V is way out of the range for a 208V machine, a "Edison tap" may mean that it requires a neutral because it 120/208V, without seeing it just taking a guess.

[Darcy Warner]

It's probably 2 phase, yes that is a thing.

[Rollie Meyers]

It's probably 2 phase, yes that is a thing.


Not being 208V. 2Ø is 240V.

[David Kumm]

The Practicalmachinist forum has some great electrical info. Someone there will know about two phase systems and how to convert to it. Dave

[Darcy Warner]

Not being 208V. 2Ø is 240V.


the area of the country he is in had extensive 2 phase power supply.

There was never 240v supplied then.

[Art Mann]

There is no such thing as "2 phase" power. What people call 2 phase is single phase with 2 hot leads. 208VAC is not "way out of range" for 240VAC. A great many machines are built to run on either voltage since both voltages are very common. Verify these facts with a real authority, such as a power transmission text book or an electrical engineer rather than anonymous people on the internet.

[Darcy Warner]

2 phase is a real thing. Still being distributed in parts of PA.


https://en.m.wikipedia.org/wiki/Two-phase_electric_power


Have had a couple machines that had two phase motors, one is sitting in my shop right now.

[David Kumm]

Google two phase. Lots of reading. There was such a thing prior to three phase being adopted due to advantages including lower cost as two phase needed two separate circuits ( 4 wire in total ). Three phase needs only three and runs at lower amperage so cost savings for wire was significant. Way more detail available online. Dave

[Art Mann]

I can't believe any 21st century city would still be using such a weird system. How do you run your machines? That is a true oddity. How do they produce a 90 degree phase shift with modern generators? When people talk about 2 phase, they are really talking about single phase coming off a transformer with a grounded center tap.


2 phase is a real thing. Still being distributed in parts of PA.


https://en.m.wikipedia.org/wiki/Two-phase_electric_power


Have had a couple machines that had two phase motors, one is sitting in my shop right now.

[Darcy Warner]

The motor in my Whitney had been rewound to 3phasr at one point, but it came from the factory as two phase.

[David Kumm]

For those of us with old machinery, two phase is about as common as 200v machines. I run across a few every year. I'm sure Darcy sees more. Dave

[Martin Wasner]

I need to take a peak at the motor plate on the Tannewitz and see if it was ever rewound.

Electricity is basically magic to me. As far as I'm concerned all electricians received their training at Hogwarts.

[Greg R Bradley]

..... When people talk about 2 phase, they are really talking about single phase coming off a transformer with a grounded center tap.
That is Split-Phase, NOT 2 Phase. But I've heard a lot of people call it 2 phase also.

[Art Mann]

Split phase is a much better term since the single phase voltage out of the transformer is split by the center tap.

[Phillip Gregory]

Looking at the machine's data plate and the motor's data plate will tell you for sure.

- 208 volts is a "modern" voltage as it is the phase to phase voltage from a 120/208Y three phase transformer. "Old" voltages from the days when 2 phase was still around were 110, 220, 440, and 550. You would not get 208 volts from any setup that would make those voltages.

- Single-phase motors that are actually rated to run on 208 volts nearly always are rated as 208-230 volts and can be run on common residential 240 volt service. (For some reason 240 volt motors are listed as "230 volts," but they are designed to run on 240.) Motors that are rated to run on 208 volts only will be marked only as 200 or 208 volts, and will very likely be 3 phase. Motors not specifically listing 208 volts as an acceptable voltage will NOT run well on 240 volts as it is out of the tolerance band of a motor rated at 230 volts. Some people will still try to do so, however.

- The "two hots and an Edison tap" means your machine has something in it such as a light or the magnetic starter's contactor coil that runs on 120 volts. "Edison tap" is stagehand slang for a typical 120 volt NEMA 5 receptacle and might mean the machine has a separate 120 volt plug for that circuit in addition to and separate from the 208 volt power circuit.

- You can run a 208 volt *3 phase* motor from standard residential 240 volt service by using a VFD that allows you to set maximum output voltage to something less than line voltage (many of them will let you do that.) You would need a 208 to 240 volt buck/boost transformer to run a truly 208 volt only single phase motor on 240 volts.

- If you actually do have a 2 phase piece of equipment, you can power it from single-phase power of appropriate voltage by putting a suitably-sized motor run capacitor between the power lead for one winding and the power cable. The capacitor will shift the phase by 90 degrees and allow the motor to operate.