Electrical Wiring in the Home/Doerr


QUESTION: Need a wiring diagram for a Doerr 2 hp compressor motor,its wired at
220v now its PH1 60 hz.See all the numbers on the wires, nedd any help you can give me ,Thanks!

ANSWER: Zac, [This is the second answer, the first did a lot of weird blipping when I hit send, so maybe it did not make the trip]

 I need the motor lead numbers, as they are connected now if possible,     if you have not disconnected, please take a photo for your own information and knowing how they connected the motor for low voltage   this will tell us how to connect it for high.

Most likely you have a cap start or cap start cap run motor,   if it states compressor duty on the motor.

Because a motor is running a compressor,  does not necessarily mean it is a compressor duty motor,  I have seen all kinds of improper motors belted or coupled to compressors,   

Most likely you have some P leads,    and most likely at 110 volt connected,  most all motor leads are on line,    

The engineering is to put the motor windings in series for high,  and in parallel for low.

Take a close look at the under side of any connection covers,  and look for real small print at the bottom of the nameplate, they like to hide the connection data.

BELOW is an example from another user attempting to make a voltage change on a Doerr, now EMERSON by the way, and finding old Doerr info from Emerson is not real likely. So see the discussion below: [note the questioner missed the notations on where to connect the incoming lines,   I PUT THE !!!!!!!!!!!!!!!!!  outside of the conversation which indicates where the line connects to the motor, the questioner missed the notations.
Diagram on motor shows:

P1 ungr'd line          220 line here !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
P2 Tape
T8 \
T3   Tape (T8, T3, T2 drawn as joined and labled "Tape")
T2 /
T5 \  
T4 / (T5 and T4 drawn as joined and labled "Line") 220 line here !!!!!!!!!!!!!!!!!!

RPM  - 3450
Frame - rigid Base K56H
Application - Air Compressor
Enclosure - ? (regular electric motor)
Single Phase
Continuous Duty

Where do I connect the wires to make this 230v?

It is normal for many compressor motors to have a set direction, but in this case it reverses,   reversing is simply swapping   motor leads  5 and 8.


Above is a long link to a ton of Doerr connections,  if you find a mate to yours,  you can follow the connections, [some are impossible to read so you will have to look through the photos closely]

If after looking at the link and you are still not sure, or concerned, I need the numbers you have, and how they are connected for 110,  a photo works fine,   if you will separate the leads so I can see them,  or jot down the numbers and what is taped to what.

Next if this is a compressor duty motor you will see one two or three cans on the top of the motor frame,

  take them off and inspect the wiring to the capacitors, look for bulging of any capacitor and also look at the top or connection end of the caps,  there will be a small circular area,  these are relief ports, if any are puffed out, or blown out,  replace the caps.

At the cost of running a two HP motor, which is NOT CHEAP,  I would invest in all new caps, if it were mine, as the run cap does stay on line and helps with the power factor,  by helping the run windings.

Next find yourself some compressed air  DRY  and if the motor is open or has vents to the inside,  slowly turn the shaft and blow into the vents,  turn the motor upside down and do the same, then reverse the procedure,   

Many compressor duty motors are found with wood working machines, and wood dust will collect inside,  this can hold the start switch open,  and prevent the motor from starting.

Next do not use a BREAKER as a switch. Breakers are designed to trip several times, but not designed as a switch.

I would suggest for no more than the cost will be, a fused disconnect,   with two slow blow fuses.  Breakers protect wire, not devices.  And are too slow to react to protect a motor.

Lastly,  on the wood subject,  many compressors and motors are located in the shop area,  and wood dust is extremely explosive, when contained and concentrated.

An arc from an internal start switch can set off the dust and you want no part of that.

So be sure you keep the motor away from any kind of dust if that is the case,  and rig up some sort of evacuation system to remove air borne dust and contaminates.

Lastly  you will have two leads for your 220 and you need a dedicated ground,  from the main to disconnect to motor frame.  Do not use a neutral,  use the earth ground from the main ground buss.

If after looking through the example above, and through the link of various Doerr connections and still are unsure,   snap me a photo or at the very least provide me a diagram of what is connected to what by numbers.

Motor leads are designated by a T to differentiate motor leads, from power wires.

And many leave off the Ts, so if no Ts, not a problem.

Make sure your run of 220 is adequate for the distance,  there are charts on the net or give me the details and I will size it for you.

If you have any questions, write me back with photos or jotted down info, and we will figure this out.

Take no chances on anything you are not sure of,   and watch the P leads if your motor has them.

P is for protection,   there may or may not be a reset switch or red button on the motor.

If not,  there should be a warning that says something like  "caution motor will and can start without warning".

The reason for that, is these crappy internal protectors are nothing more than bi-metal switches buried in the windings.  Given enough heat, the metallic switches will move and open the circuit,  shutting down the motor.

If that happens, you need to find out why, it tripped on over temp,   it could be over current, voltage issues, dirt and contaminates in the motor [which you already dealt with as you could with the compressed air] but sometimes it cakes on and will not blow out.

The internal thermal can become weak after just a few trips,  and then it is even more worthless.

The protection used to be a separate circuit,  with two leads to tie across the starter coil,   but the changes over the years, put the bi-metal switches in series with the run windings,  so there is your starting without warning,   as the metal cools it closes and if power is still at the main connections,  it will take off.

So a bit more than you asked for, but there are so many of these compressors around wood shops that a fair warning is in order.

Be cautious of rotation,   if the motor is reversible,  you want to run the motor and verify it matches the compressor direction, or you can trash a compressor in a heart beat.

Anything at all you are not sure of,  let me know, and I will walk you though whatever is needed.

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

QUESTION: I guess I confused you , it was wired for 220v and im trying to wire it
back to  110v. I can read yhe diagram on the moter I was just hoping
That someone might have a drsawed out diagram. The leads I believe are
P1, p2, t4, t5, t2, t3, t8 it just dont want to do it wronh and burn up my
motor there very costly. Thank any help hreatly appericated

Where do I connect the wires to make this 230v?   Yep I am confused as this statement was below the nameplate data,,,,,,,,,,,,

It should look like this link   


P1 to the ungrounded line side of your 110  [the white or neutral]

Electrically connect and isolate P2 T8 and T3  in a bundle and isolate means tape up, but the wires will be bare on the ends and twisted together then taped use a wire nut

T2 T5 and T4 are connected to the black or hot side of the 110 Volt supply  you will use a wire nut and tape them to the incoming black line

NOTE  P2 is in the non line bundle       T2  is with T5 and T4 and the black or hot side of the 110 volts,    these numbers match the numbers you provided and are fairly standard for a motor with P leads which stands for protection    a thermal protector,   buried in the windings, but don't confuse the P2 with the T2    and it is easy to do that,  it is a stupid way of marking something but that is how they do it,          

NEXT if any of this is different than the connection on the motor use the diagram on the motor.

The link above does show it drawn [at least a few inches of each lead

So to recap on 110 volts    and you should find someone to measure your voltage   I have been in homes where the low side voltage is over 130 volts,  and the high side over 259   they were blowing light bulbs every two weeks,    it is due to most likely an incorrect tap on the transfer on the outside,  nothing you can do about it, but have them correct it, but you should know what your voltage is,     while voltages do change during the day and time of year,  at least get one reading and make sure it is not out of wack   it won't be 110    115 or even 120 is more the norm these days with all the electronics   

110/220 is sort of a carry over from the days when voltages were just 110 and I doubt the motor even says 110       the connections may say on the nameplate   low and high and not even list a numbered voltage   but that is no concern,    motors will run fine as long as you don't below or above 10% even 15% of the rated voltage stamped on the motor,

Next thing now that we have the low voltage connection      if it runs the wrong direction   swap  T5 with T8    wired just like it says above or on the link or on the motor,  but take the T5 and put it where the T8 was   and the T8 where the T5 was    a simple swap  everything else remains the same,       

Yes they are expensive,    are you having to replace motors often on one or more appliances or devices?   by often I mean once every few years or more often,      

Motors if wired correctly supplied with the rated voltage and in the tolerance range,  with the motor aligned straight to whatever load,  by a belt or a coupling or even shoved into a blower wheel,     the belts need to be straight  or the coupling needs to be to dialed in with an indicator so it is has a straight line through the connected shafts in all planes,    

If belted the tension should not be so tight you could bounce a quarter off it,   that is too tight, and too much radial load,  it should not flop nor be super tight  a bit of flex in the belt[s] is what you want,     

Then lastly if the motors are dying often you really need to look into the value of the voltage,  the alignment or whatever it is connected to,     and find the reason,   a motor should last maybe even a decade or more  if there is not some external forces causing it to fail,       

Next the size of wire for the amps is critical over the distance it is run,  there are charts all over the internet that give you the wire size for a particular amperage,   you look above the low voltage on the nameplate and it will show you the loaded current,   make sure your wire size is adequate or larger for the current      

Next it has a protector inside, but they are not very fast to trip,    and maybe a red reset button,  if that button trips often  something is not right,    find out what it is,   

Lastly  breakers in main panels protect wire   not NOT devices     I advise that motors be run through a fused disconnect,   a dual element fuse on both leads  or at least the hot or black lead,    not that expensive and will do a much better job of protecting the motor than the internal protector or the breaker       breakers are too slow also,     

one more lastly    breakers are not switches     not designed to be switched off and on with any short durations  such as daily     if nothing else get a timer switch or some sort of switch   again it must handle the motor current  [in amps]  you will eventually wear out the breaker and render it useless using it as a switch,       

Clear as mud?   you have any more problems let me know and we will go back over this until we have it right     be careful while working with the motor,  these internal switches or protectors some times let the motor start up on its own as long as power is to the leads so get it installed, aligned  so you are not around the shaft    Then make your electrical connections,    and while making the connections   make sure the breaker is in the off position and put some tape over it,    red is preferred    or lock the box  turn any switchs off,   and just be careful in general,    motors not bolted down sometimes have enough kick on start up to jump off a bench,    

ONE MORE LASTLY   somewhere in or near the connection box should be a green screw,  that is for the EARTH ground  you need your black and white  [110 or low voltage and one bare copper wire as large as the power leads,  it goes to the frame usually under a green screw,   this ground leg has nothing to do with the operation of the motor, but in case of a fault it helps speed up the breaker to trip   and hopefully it saves the motor but more important if someone is touching it or around it,  you want it to trip off if there is a fault,       

Take your time and you will have no problems,    when you make your connections use the correct size wire nut then tape all over the nut so the nut cannot come loose from the wire or wires          and again if unsure about anything,   write me back and there is no dumb questions so ask if not perfectly clear,  
About Electrical Wiring in the Home
This site answers questions related to home electrical wiring, home wiring, general electrical help,and other electrical questions related to aleternating current (AC). You can find help on the National Electical Code, home electrical issues, wiring electrical outlets, installing lighting, electrical grounding, and general electrical help for do-it-yourself projects not require an electrician. If you do not see your home electrical wiring question answered in this area then please ask your electrical wiring question here

Electrical Wiring in the Home

All Answers

Answers by Expert:

Ask Experts


Will Babbitt


Electrical issues of all types, wiring, control, appliances, components, specialty in Electric MOTOR or APPARATUS trouble shooting, electric motors, electrical problems, single phase, three phase, DC, capacitors, elevator MG-Sets, modifications, reverse engineering, VFD Drives, single to three phase convertors. Repair of most any electrical/mechanical/electronic apparatus, OEM, AC, DC, Industrial Applications, Three phase, single phase failure mode, determining the root cause of the equipment failure BEFORE failure repeats, Antique appliances, electric motors, fans, ceiling fans, base mount fans, poor equipment performance, Modifications, habitual failures, vibration, redesign, obsolete issues, collectible items restored, rewinding. Owner of EMR Repair Inc www.emrrepair.com More information on electric motors, under Engineering/Motors Ask about any electrical or mechanical problems in the home, office, or even at your work. B2B or business to business CONSULTING I can do but it would be a much more complex issue, that would require a significant amount of time. repair@mearservice.com from there we can discuss and begin work on about anything. Industrial electric motors, controls, troubleshooting, vibration, alignment, any type of industrial or commercial electric/electrcical equipment For the home owner, renter, apartment if you have odd things going on, describe to me, photos are normally very helpful, appliances, heating and air conditioning issues, light switches, installation, DIY PROJECTS FOR THOSE NOT EDUCATED IN ELECTRICAL, we can do some things, but for safety and sanity reasons, I may refer you to a local electrician, and help you find one, help you with pricing and even speak directly with anyone you hire if you have issues,


Over thirty years with a major repair and sales company, VP of Operations, and former owner of my own specialty repair shops, MEAR Services local to Kansas City Missouri EMR Repair Inc., located in Kansas City Missouri, 2014 sold both businesses to JCI Industries, Lee's Summit Missouri wbabbitt@jciind.com Evaluation and repair of electrical/mechanical apparatus. Electrical and mechanical repairs, trouble shooting including, vibration and balance issues. About.com provides this service, and the huge costs to provide help on about any subject. They provide the servers, the people to vet the experts, costs that would be the same as operating a good sized business, They should be appreciated for what they do, the huge costs and the great help they provide for free, Electric motor questions, can be answered here but there is a dedicated category that has other experts to help and add to a solution. Other common questions, are noises in the walls, breakers tripping, devices not starting or shutting down for no apparent reason, smoke alarms buzzing, thermostat change outs, or sizing wire or needing information for a new project, but anything can be resolved, anything, with enough effort and patience, DIY, with electrical is possible, but in most cases the use of a simple ohm meter or volt meter is needed, they can be purchased at any hardware store for a few bucks. If you have smoke, or smell smoke, don't be writing me, call 911 the Fire Department has no problem looking for smoke smells, better then spraying water on a blazing fire. DO NOT GET CAUGHT INVESTIGATING AND TRAPPED IN A BASEMENT LOOKING FOR A BLOWER FAILING< As to the tip jar, it is up to you, it is appreciated, every expert spends out of pocket that I know, we spend on IP time, computer wear, printing documents, books, and of course our time, but if we prevent a $400 service call, we did well,

Former IBEW, EASA, IEEE, UL, ..............


10 plus years, various Technical Schools, followed by Industrial College Credit and non Credit Courses, electronics courses, experience in most any electrical apparatus, electric motors and generators, AC OR DC, fractional to above 5000HP, other electrical apparatus, slip rings, sleeve [plain] bearings, lubrication, identification-no data plate, control components, service and sales. I have continued night schools for decades, the list is extensive. I have been in the business of repairing most anything with wires or mechanical parts for decades, I have some helpful hints and directions you won't have to dig up. Or hopefully not have to pay a huge service call invoice to find.

Awards and Honors

Past/Present Clients
Federal Government, National Weather Service, NOAA, Commercial Power Plants, Major Vehicle Manufacturers, Printers, Other industrial and Commercial Businesses

©2016 About.com. All rights reserved.