You are here:

Electric Motors/3 phase switch


QUESTION: We have a sander that was previously wired for 240 3 ph. We have since switched to 440 3 ph, and now need to rewire the motor for this new 3 ph. The terminal plate has W2 U2 and V2 going to a contact and then U1 V1 and W1 going to a seprate contact. Just trying to figure out which terminals i need to switch to get to a 440v set up.

ANSWER: Chris  

Simple answer,    put U1  V1 and W1 on the new 460 line,   defeat any kind of dual contactors that might be paralleling the leads,     or leave the [2] leads off      bundle W2 with V2 and W2  this will make a wye point,      electrically connect and isolate and insulate,

  so if there is a wye delta contactor built into the sander you can defeat it,   or just put the [1] leads on the second contactor that brings in the incoming power,       and let the first part of the starter do nothing,   if that is easier,    remember this is not a dual voltage motor without nine leads,   it is 58% or 1.73  percent  however you want to look at it,   of the rated voltage,   so pay attention to the running current,       

Below I will explain the setup and it is confusing,   but to just say put three leads on the new 460 and not warn you this is not a true dual voltage motor would not be right,    so you need to monitor the running current,    as we will have no idea what that amperage is until it is under power,   most likely it will operate without much fuss,  but if it doesn't  I have tried to explain all the circumstances and what you are dealing with,      

I need to explain 6 lead three phase a little first,    it is normally  workable but it is not as exacting as nine leads.

You threw a ringer at me when you say the sander is wired for 240 volts and you have TWO CONTACTORS.

I understand it,  but it is hard to explain and even harder to know exactly what you have.

If you could go here :

This link will give you the majority of three phase motor connections,  for now and future reference.

The motor lead convention using the UVW   is the IEC or SHOULD BE THE IEC convention of three phase motor connections.

However,  with 6 leads  as opposed to 9   it is electrically and physically impossible to configure a connection that is half the voltage rating of the other.

Or I can say it this way,   with 6 leads  as opposed to 9  it is electrically and physically impossible to configure a connection that is twice the voltage rating of the other.

Example with 9 leads,   when connected for low voltage   three phase   WHATEVER the low rating is in an empirical value,     the high is twice that.  EXACTLY.

And we can look at that the same way with the high voltage rating,     the low connection is one half the high rating      WHATEVER THAT IS.

A NEMA 9 lead motor could be rated   220  low    then it is 440 high.

Or if it is 460 high   it is 230 low.

And normally a three phase electric motor is forgiving enough,   that if you have exactly 440 available to you,    and you have a motor rated 230/460, or 240/480    the high connections even though they are higher than your available voltage.

As you said   you had 240 volts,  now you have 440 volts,   that could be right on the nose,  or just a loose slang for low and high "standard"  US three phase voltages.

The only way to know wherever the voltage is located,   an old building a new building,  a new or old service,   the power in is a result of the exact transformer the voltage available at the pole, the number of taps on the main transformer,  so on,    

So it is speaking in very general terms.

Only a volt meter will tell you what voltage you have.

Then when we look at your sander,   what voltages does it say it is rated for?

I have seen where some manufacturers use a very liberal rating of a 6 lead motor.

You cannot get half or twice with just 6 leads,  as we know,   but I know they put high voltage and low voltage ratings on devices,  and are not accurate in reality,  they are counting on the average or median ratings and the motor to withstand applied voltages way more than the normal 10 percent variation.

I am going to assume this is no hand held sander,  and probably a fairly expensive and elaborate sander.

As you look at the IEC chart on the link above,

on the left side of the chart  you will see the 9 lead  wye and double wye connections,  then the delta and double delta connections.

Those are true half or twice of the low or high rating of the motor,   whatever WHATEVER IT IS.  If it were designed and rated for 160 volts low,  the high would be 320

I am explaining all this because I have no idea what your sander is rated for,   but with 6 leads you cannot get half or twice of one voltage rating.

Now most of the time the motor will operate way off the normal 10 percent,   and at this point  you have only one option,    other than having the motor wound to exactly the new voltage you have available  which you state as 460 volts,    and I am not sure if it is exactly 460 measured or as it usually goes,  it is more slang than empirical values.

What I DO NOT want to happen is for this sander to not be as tolerant as many motors,  and then you have too much current in one scenario OR a low voltage even low performance scenario without you understanding what you are dealing with .

It is impossible to know how a motor reacts to applied voltages above or below their manufactured ratings.

When we do a motor class,  we pick several motors of several types and vintages,   older with much lower ratings,   220/440   to more modern ratings which are becoming 240/480.

Pick a motor,   and the motor we pick is rated for 460 volts high and connected for that.

We match up a dyno load say it is 1 HP,        at 460 volts when the motor is put under load,  it matches up with the amp rating on the nameplate,   

With some motors, when we lower the voltage to say 440  not much change,  if any

Because three phase is so forgiving    generally speaking   

But we know at some point     some where some value,     that motor is not going to like the voltage applied,  but what value that is varies from motor to motor.

We might get clear down to 390 volts before we see either current or performance start to get out of hand.

Some motors will actually operate better at a lower voltage,  and some better at a higher voltage,    

All you will get from NEMA, or your utility is this 10% tolerance.

So you see the dual voltage connections at the top under the heading
THREE PHASE I E C MOTORS   on the left side of the chart, AT THE LOWER CORNER


With your motor,  you have six lead which is not dual voltage yet they are connected that way all the time,  and again many operate fine, some are acceptable not right, but acceptable,   and some just fall flat,    so if that happens,  you know what you are dealing with.

It gets confusing because all these slang values are thrown around

You have as stated  a sander wired for 240  and now you have  440 volts    

The sander is rated for something,   what I don't know,  but as you see,  6 leads are SINGLE voltage connections,

However motors are run on wye on the high voltage supply,  and on delta for a low voltage supply  and I use the high and low very loosely     I have no idea what the ratings are,  what the current draw was at 240 if it even was actually 240   it could have been 232

    voltages again  are often referred to in slang or general terms,    240 or 220 or 230 is considered low, and 440, 460, 480 are considered high

So with your terminal plate showing the U1  V1  W1 to one set of contacts,  then the U2 V2 and W2  to another set of contacts,    

Most likely what they are doing is allowing for wye starting and delta running,    that would put the leads in NEMA   like this     

U1 = T1     V1 = T2   W1 = T3

U2 = T4     V2 =T5    W2 = T6    

See the different order on the terminal plate  of the 1s versus the 2s?

That is designed to tell you to wire the motor as a delta when it is running,  and if you need to lower the inrush current   you can start it wye  and then the two contactors close and put the motor in the delta configuration.

I don't know if you are starting across the line,   if the sander has a wye delta contactor as part of it's controls,    

But at this point all we have for choices are to run this motor in a WYE connection,  the highest most series connection we have available with only 6 leads,    

If the sander is currently running off a wye delta contactor,  you will have to defeat that,   

You will need to connect the 2s  the U2 and V2 and W2  all together,  in a wye.

Then your new 460 line will go to the 1s    U1  V1  W1

How far off from the rated voltage we will be, no way for me to know without all the data plate info,       

The reason the terminal plate has the leads in the orders they do is this     

Delta [low voltage] in NEMA   is  T  1,6.7  to line,   2,4,8 to line  3,5,9 for low   

Wye  [high voltage] in NEMA   is   T  1 to line,   2 to line   3 to line,    4 with 7 tied electrically and isolated   ISOLATED AND INSULATED     5 with 8,  then 6 with 9

When you only have 6 leads,   you use the 1 through 6 to make your delta   the same way   so that would line up   and referring to my cross chart above   

you end up like this

UI [T1] with W2 [T6]     TO LINE

V1 [T2] with U2 [T4]     TO LINE

W1 [T3] with V2 [T5]     To LINE

See how the order of one set of contacts lines up with the other making the motor leads into a delta,  [less the missing 7.8.9]


So with all that and it is confusing,   and believe me this gets messed up all the time,   all we have a choice is to use the wye  of the available 6 leads to get the highest rating on the motor we can get.

So defeat any type of dual contactors,   or leave the [2] leads off and bundled together and electrically connected  isolated and insulated     and let the contactor do nothing except close down on the [1] leads,      

I don't know if you have a contactor setup as part of the sander,   and how you chose to use it,  is what is best for you to do,      but there will be no soft start  running the motor on only three of the 6 leads,      

Also at 58%  or 1.73  going the other way,   we will not know the running current until you try it,    as the incoming might be  spoken as 460  but measured at 452

You will need to bump for rotation,   as their will be no relationship of phases from the original 240 volts,   unless whomever installed it did a phase identification and left you with a chart or matched a incoming terminal,    rarely done,  normally they just put in the three phase and let you bump if rotation is an issue.

Then because we know the motor is not 240/480    it is a percentage of whatever voltage rating it states,    and look at the cycles,   it very well could be 50 cycle rated,        

So pay attention to the current of the motor on the sander and other motors,  that may be on the new three phase,      measure it, and make sure it is balanced,  you do not want 460. 451, 455    that kind of unbalance can create more havoc with motors than over or under voltage,   

To recap        you have a single vcltage motor,  that we are going to use the wye connection as high,    and hopefully    and again often,   the motor is able to operate with the voltage not being within the 10% variation or tolerance which is a rule of thumb.

If you get confused or need more help  let me know,  my shop phone is 816-650-4030   MEAR Services,   if I am not there Richard would be able to walk you through it,     but it is fairly simple   as there are not any choices,   but to put the 1 leads on line,   and bundle the 2s

As a side note,  all you have is three phases in the motor,   the six leads are the ends of each winding phase,     1 comes out 4   1 comes out 5      3 comes out 6       so you could put power to the 2s and tie the [1s] together and have the same thing,   

It is just a matter of what current you get compared to what the nameplate rating is,    

If there is a service factor on the motor,    it might be written as  S.F. 1.00 which is no service factor   or  maybe   S.F  1.15  which gives you 15% above the rated HP and can run the motor constant duty to that 15%  over rated HP   or torque   or however it is rated,  

Although it is not explained this way,  if you have a service factor of whatever,   you can use that percentage with voltage, amperage, and or load,     and the motor should run constantly without an issue,       

Again no one ever knows,   some motors like over voltage,  some like under voltage,  and how much is motor to motor,    

also my our shop email is     if you need to get in touch that way,   or you can come back through all experts,         

If you have any issues at least you should know what the likely issue is,        

The blurb below is from

Assuming you are in North America, don't get hung up on the "Delta vs Wye" winding issue, it is almost completely irrelevant. A NEMA designed motor is what it is, you usually have no way of knowing, short of dissection, whether it is wound in Delta or Wye internally, nor should you care.

Don't confuse this with Delta or Wye power systems, the issues are completely separate and not related as far as functionality goes. Aside from Y-Start / Delta-Run motors, you ALWAYS only run 3 leads to the motor, NEVER the 4th (neutral). So how it is connected internally is for the motor mfr. to worry about, not you.

In a Wye-Start / Delta Run motor, the windings, and associated power ratings, are still based on the Delta configuration. But when you bring all of the motor leads out to the connection box and connect them in Wye, you get the 1.73 reduction factor (58%) on effective voltage across the windings. Since torque, and therefore current, follow the square of the applied voltage, you also get 33% (.58 x .58) of the normal torque and current. Since the frequency didn't change and you have less torque, you have less HP by the same ratio, so your shaft HP is down to 33% as well. Technically then, you could run a motor in Wye continuously is you are ABSOLUTELY sure the mechanical load on it is never more than 1/3 of its rating (although you must as "Why?")

How that relates to "Leads" in single speed NEMA motors is as follows:
"6 lead motors" are either single voltage motors, Wye or Delta wound (you won't know the difference) or they are single voltage, Wye-Dela start. They can also be dual-windings, for instance as you would use with a Part Winding starter. In some RARE instances they are dual voltage motors, but the voltage ratio is always 1.732:1, so that would be 480/277V or 575/331V; you won't see a lot of those, not worth considering.

"9 lead motors" can be either Dual Voltage Wye or Dual Voltage Delta (again, you won't know the difference), typically 230/460V. They CANNOT be connected for Wye-start / Delta Run. In some rare cases you will see IEC motors sold in N. America as Single Voltage 9 lead motors, because they base it only on the high voltage connection (Wye only).

"12 lead motors" are where you get into all kinds of possibilities, i.e. dual voltage, Wye-Delta starting or pretty much any lower configuration mentioned above.

In the IEC motor world, more specifically Great Britain (and Australia / New Zealand), THEY use Delta or Wye winding configurations for voltage changing. A 380/220V motor is connected with its windings in "Star" (Wye) for 380V line supply, Delta for 220V (380 / 1.732 = 220). Their system essentially rates the motor based on the Delta configuration as well, but because you are changing the applied voltage, the power remains the same. We don't do that here in the US because we don't have the same ratios of voltage supplies.

---------- FOLLOW-UP ----------

QUESTION: Let me start by thanking you for a detailed and thorough explanation. I want to correct my statement that it had two contactors, it has one. The other is an overload relay. I miss traced those in a hurry. Also the motor plate say its rated for 230/400. Based on the info you gave I'm pretty confident we can get this switched over. Again I appreciated the fast response.

You a

you are very welcome,   and wouldn't you know it,  1 of a 1000 are rated correctly when they have IEC 6 leads,     and yours is,    rated correctly        230/400 would be the delta then wye voltage rating,       so if only one contactor,  then all you need to do is put all the 1s on line or all the 2s    I would use the 1s just for keeping with IEC numbering,     now it will depend on the motor, if it likes the 460  and if it is a true 60 volts over,  that overload might give you some fits,    especially on inrush  [start up]   

A standard three phase induction motor will see 4 to 8 times full load current,   the higher voltage should spike the inrush at a high rate,    so if it is adjustable   and it trips you know what to do,

remember to bump for rotation,   and get a clamp on on it  asap  so you can gauge the running current,      now most will   feel the frame of the motor if they suspect a problem    

The motor frame is how the motor cools,   Totally enclosed with a fan on the back and maybe fins,  for heat sinks     blows air over the motor and removes the heat,   

Open drip motors still cool with maybe an internal fan on the rotor,  maybe drawing some ambient air in the bottom    but they too cool by convection  without the fan to blow across it,    so if the case is hot,  it is normal,  to a point,     

So a hot motor frame will tell you nothing,   only using some sort of laser thermal gun will help if you find hot SPOTS   that is a sign of shorted laminations inside the motor,   or even a possible short,    but most will show about the same temp across the entire frame,  

So good luck and while you are somewhat over the 10%  I have a feeling if they were good enough to actually rate the motor for dual,  they have taken into account that many may use the motor on a voltage over 400 as 380 is a overseas standard,      400 is not standard anywhere    except for high freq applications,  for some reason  if you see super high hertz there a lot of 400 volt  180 or higher hertz,  but normal 60 US   is now days more to the 480 rating  as utilities have had to bump the amount of power with the increased needs    

Good luck and if you need anything,    you know how to find me  

Electric Motors

All Answers

Answers by Expert:

Ask Experts




Three phase/ AC DC single phase motors, controls, any problems or failures, motor installation, performance issues, connections. All other electric motors/gearboxes/apparatus. Specialty repair concerns, obsolete motors and solutions. Other mechanical or specialty equipment. See my profile under Home/electrical at this site


30 plus years in the electrical motor and apparatus repair industry. VP level management of repair facilities, current owner of my own specialty repair and consulting firm.

EASA, IBEW [retired], other specialty organizations, Lubrication, Vibration EDI, Tribo-electric Councils

Currently fielding concerns at this site under "Home Electrical"

4 year technical, College level specific courses, EASA repair courses, vibration analysis electronic and electrical trade school.

©2016 All rights reserved.