rambo2_981
Plastic
- Joined
- Aug 5, 2015
I was told an older woodworking 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, 240V that we're all familiar with?
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Largest Manufacturing Technology Community on the Web
Stay Connected:
208V 2 hots edison tap
- Thread starter rambo2_981
- Start date
- Replies 73
- Views 10,299
6PTsocket
Aluminum
- Joined
- Jun 29, 2014
- Location
- Jackson,NJ
There is no single phase 208 feed unless you mean the 208 voltage that is across any 2 legs of of a 3 phase feed. Neutral is not used for 3 phase power but you can get a 120 volt feed between any of the 3 phases and neutral. With single phase 240 volts, both legs are hot. There is 120 volts between either hot leg and neutral. A 240 volt device running on 208 will have reduced power if the device is rated to run on either voltage at all. There is a solution that is not that expensive and I have used it They make 208 to 240 step up transformers. Make sure it is rated for the current you need.
Sent from my SM-G900V using Tapatalk
Sent from my SM-G900V using Tapatalk
6PTsocket
Aluminum
- Joined
- Jun 29, 2014
- Location
- Jackson,NJ
I have not a clue what an edison tap is unless he meant neutral. There is 120 volts between any of the 3 phases of 208 and neutral. There is 208 between any two phases of a 3 phase feed. 240 volt devices running on 208 have reduced power. I don't know if 208 devices can tolerate 240. Some are made to handle either and some are not. If you are sure it is a single phase 208 device, there is a simple solution. They make 208 to 240 autoformers. You can use it either way to step up or down. Just make sure it has the proper current rating for the device.
Sent from my SM-G900V using Tapatalk
6PTsocket
Aluminum
- Joined
- Jun 29, 2014
- Location
- Jackson,NJ
That is describing a 240 feed and a neutral which is what is fed to virtually all private homes. It discusses why it is used. Since I am not a power distribution engineer I just deal with what I have to work with and let them worry about supplying it. The OP was discussing a 208 volt three phase feed which is supplied to industrial users. It is not the split phase in your link.
Sent from my SM-G900V using Tapatalk
Lakeside53
Stainless
- Joined
- Sep 28, 2007
- Location
- Woodinville, WA
It's also most "commercial buildings". 208 volt from any two legs of three phase delta-wye distribution is single phase, and as has been stated in prior posts, 120 from any leg to neutral. From an end-user perspective, two legs of 208 is identical to 240 split-phase distribution apart from the slightly lower voltage. Simple buck/boost transformers can be used to adjust if really required; mostly it is ignored unless you need to run a motor to full ratings and it is not labeled for 208.
TGTool
Titanium
- Joined
- Sep 22, 2006
- Location
- Stillwater, Oklahoma
Pardon, but the OP specifically said single phase. Where did three phase arrive in his query?
6PTsocket
Aluminum
- Joined
- Jun 29, 2014
- Location
- Jackson,NJ
Because 208 is only supplied as 3 phase power. Nobody is supplied with just two of the three legs that yields the single phase 208 the OP is talking about. That is as improbable as your power company supplying you with only one leg of 240 and a neutral for 120 only service. They do not go to the trouble of distributing 3 phase to feed only 2/3 of it to any customer. This is what is normally distributed to commercial and industrial customers.
Sent from my SM-G900V using Tapatalk
SeymourDumore
Diamond
- Joined
- Aug 2, 2005
- Location
- CT
That is correct.
Except for virtually all commercial offices, residential towers, larger residential complexes, condos etc. etc. etc.
The POCO sure as hell ain't gonna install both, 3PH-Wye AND single phase 240 service.
For an almost guaranteed test, just sneak into your local hospital or medical center and plug your meter into any of the single phase outlets.
You will find a proper 208V reading.
Now as to what an "Edison" tap is?
EPAIII
Diamond
- Joined
- Nov 23, 2003
- Location
- Beaumont, TX, USA
Been around for 73 years, most of it working with electricity, and I have never heard the term "Edison Tap". I tried an internet search and this was the best return:
EDISON TAPS
As for the basic question, I do know that 220/240 Volt motors can be run on 208 Volts. I ran a mill that way once and it worked just fine. I did not measure it's torque, but it seemed to cut whatever I wanted it to cut. Now, is the motor on that machine actually 208 Volts? I guess it is possible. Perhaps it is a three phase motor that has some type of Phase Converter installed to allow it to run on two legs only, but I don't really know why that would have been done. More likely, it is a 220-240 Volt motor and it was being run on a three phase system as I described above.
Do look at the motor's nameplate to see just what it requires. And look for any added circuitry that may have converted it to something else. You may have to restore the original wiring.
Can a true 208 Volt motor be run on 220/240 Volts? Probably, but there are no guarantees. It could overheat if run with a heavy load (overloaded).
EDISON TAPS
As for the basic question, I do know that 220/240 Volt motors can be run on 208 Volts. I ran a mill that way once and it worked just fine. I did not measure it's torque, but it seemed to cut whatever I wanted it to cut. Now, is the motor on that machine actually 208 Volts? I guess it is possible. Perhaps it is a three phase motor that has some type of Phase Converter installed to allow it to run on two legs only, but I don't really know why that would have been done. More likely, it is a 220-240 Volt motor and it was being run on a three phase system as I described above.
Do look at the motor's nameplate to see just what it requires. And look for any added circuitry that may have converted it to something else. You may have to restore the original wiring.
Can a true 208 Volt motor be run on 220/240 Volts? Probably, but there are no guarantees. It could overheat if run with a heavy load (overloaded).
Lakeside53
Stainless
- Joined
- Sep 28, 2007
- Location
- Woodinville, WA
A "208" motor running at it's rated horsepower will use slightly less current at 240.
SeymourDumore
Diamond
- Joined
- Aug 2, 2005
- Location
- CT
Oh come on guys!!!
This isn't a sensitive electronic test equipment we're talking about!
It's a freakin' AC motor!
And the fact that it's on an older woodworking machine, it is likely as simple of an AC induction motor as induction motors get!
So if it's rated for X amps @ 240V, then it will draw X*1.16 amps @ 208V.
Can a plane-jane AC induction motor without any brains handle a +/- 15% supply variation on it's own?
I for one sure hope so!
So, unless someone much smarter than I pipes up and defines what an "Edison" leg means, that single phase motor should run
just fine on as low as 190V, which was a very common single phase voltage back in the 80-s when 110V was the norm in your homes!
And yes, it should also handle 260V just as well!!!
This isn't a sensitive electronic test equipment we're talking about!
It's a freakin' AC motor!
And the fact that it's on an older woodworking machine, it is likely as simple of an AC induction motor as induction motors get!
So if it's rated for X amps @ 240V, then it will draw X*1.16 amps @ 208V.
Can a plane-jane AC induction motor without any brains handle a +/- 15% supply variation on it's own?
I for one sure hope so!
So, unless someone much smarter than I pipes up and defines what an "Edison" leg means, that single phase motor should run
just fine on as low as 190V, which was a very common single phase voltage back in the 80-s when 110V was the norm in your homes!
And yes, it should also handle 260V just as well!!!
A 208V motor, without further info, would NOT be expected to run on 240 in my world. It might do, but likely would be drawing excess current due to saturation.
If LABELED for 240 then no issue, of course.
You can run it and watch current. A short time should do no harm. If no load current is higher than maybe 40% of labeled full load current, I would be suspicious.
As for "Edison tap", all I can make of that is the neutral..... The guy did invent the split voltage system.
If LABELED for 240 then no issue, of course.
You can run it and watch current. A short time should do no harm. If no load current is higher than maybe 40% of labeled full load current, I would be suspicious.
As for "Edison tap", all I can make of that is the neutral..... The guy did invent the split voltage system.
Modelman
Titanium
- Joined
- Sep 12, 2007
- Location
- Northern Illinois
That would be my guess... they want a neutral for 120V control voltage without having to supply a control transformer.
I wouldn't be so quick to assume it's an induction motor. If this is really an old woodworking machine, not something from the sixties, it could very well be a repulsion motor... a single phase AC motor with brushes: Repulsion motor - Wikipedia
We need more data off the motor plate, and the voltage rating of any motor starter coils.
Dennis
SeymourDumore
Diamond
- Joined
- Aug 2, 2005
- Location
- CT
OK, please the OP forgive me for the tangent, but...
I have lived in a condominium from 1989 through 1992.
Then, after an intermediate move, went to another condo in 1997.
The first condo had 110/192 power, while the other had 120/240.
Can you please describe how Joe Schmuck is supposed to explain what he might need for appliances to the local Home Depot Specialist?
Seriously? The difference between 208 and 240 is less than 16% and you do not expect an AC induction motor to function within that criteria?
NO I DO NOT.
UL voltage limits are 10% above and below MARKED voltage.
The 208 can be 10% low, which is about 188V. The 240V can be 10% high, which is 264V.
You are asking for a motor which works over a range of up to nearly half again the minimum voltage. A range of 76 volts above the 188.
Even if you just limited it to a minimum of 208V, you are still asking for a range of 25% on the high side. That's a lot. Even electric stoves will have very noticeable variations at that amount of voltage change.
SeymourDumore
Diamond
- Joined
- Aug 2, 2005
- Location
- CT
I get that JST, but please!
We're talking about a motor that is "old" ( as per the OP ).
Old can mean from 1980 yes?
So, back then 208 could just as easily be 192V. Correct?
Today, that 208 is often 240V. Correct?
Do you really think we have an epidemic of catastrophic old equipment failures due to voltage changes over the last 30 some odd years?
Is it optimal? By no means it is.
And yet, there are likely millions of old motors running day after day, week after week, year after year outside of their supposed 10% comfort zone.
My shop was originally built in 1979. Back then they've installed two roof ventilation units, both with a single phase 5HP motor.
The original plans specified 110V 3 PH supply ( I have the acceptance docs ), so we know that the motors ran on 192V.
Later on they've realized that 50KW furnaces draw ( and loose ) much less if they run on 240V.
So, in 1991 the outside transformer was changed to a 240V delta supply, and they've added a 240D/120Y tranny inside as a result.
And yet, the original 5HP fans remained wired to two hot legs of the incoming panel.
It is now 2017, and those motors are still original, running the very same 4' blades approx 6 hours each summer day.
192V from 1979 through 1991, and 240V from 1991 to present.
So yes, I would expect that an old woodworking machine can handle 240V single phase just as well.
That actually does make sense. Essentially they're using the motor windings as an autotransformer to give a 1/2 voltage tap.
Modelman
Titanium
- Joined
- Sep 12, 2007
- Location
- Northern Illinois
No. If that was the case, there would be no control voltage until the motor was on, but you couldn't turn the motor on until there was control voltage.
I (and I believe JST) are just thinking that the guy is calling the neutral wire the "Edison tap", tapped at the center of the winding at the transformer on the pole.
Dennis