What would you like to do?
Can you replace a 480-240V 3-phase motor with a single phase motor as a temporary replacement or will it burn it out?
Yes, you can, and it won't burn out IF>>> the horsepower rating is the SAME. Pay attention to wiring and motor rotation.
Also check the voltage: the motor voltage must be the same as the voltage between two hots of your 3 phase system. You will only use two hots as this is a single phase motor.
40 people found this useful
Was this answer useful?
Thanks for the feedback!
The load of the motor itself is constant and it will try to achieve it's running RPM. If the supply voltage decreases the amperage needed increases to where the motor wi…ndings cannot sustain the current flow without producing excessive heat. Hence, SMOKE!
A three-phase motor will not start if one or two phases aren't connected. If while running one or two phases "drop out", it will continue to run for awhile, but will eventuall…y burn out, unless connected to a motor saver.
Probably. 5 hp. is 5 hp., regardless of the phases that drive it. But for practical implementation, you will see following problems: 1] Single phase motor will deman…d for neutral connection. 2] As entire current for 5HP load will be now on single phase, your conductor will be loaded 1.732 times its rated load ( for 3 phase motor design) Hence it may call for increase in conductor cross section. 3] As entire 5 HP load will be now on single phase, your loading will be unbalanced. Single phase equivalent motor will be of slightly bigger dimension hence mounting arrangement will have to be suitably modified.
You need to ensure that each line conductor is correctly identified. If you replace them in the wrong sequence, then the new machine will run backwards when you energise it! I…t may be necessary to use a phase-sequence meter to confirm the phase-rotation before restoring supply to the new motor. As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed. Before you do any work yourself, on electrical circuits, equipment or appliances, always use a test meter to ensure the circuit is, in fact, de-energized. IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB SAFELY AND COMPETENTLY REFER THIS WORK TO QUALIFIED PROFESSIONALS.
A 3 phase 5 hp motor is a fair size motor and I must say up front that if you don't know how to, you might not should be doing so without a licensed Journeyman electrici…an. If you make one wiring mistake, the motor may burn up and they aren't cheap! With that said, a 3 phase motor has different wiring hook ups for low voltage, (208-240 volt) and high voltage ( 480 volt). A 3 phase motor has nine wire leads inside the "make up" cover. They will all have a number tag on them from 1 through 9. Your incoming three phase power of course has three "hot" legs which from left to right in the panel are A,B and C phase. These wires should be color coded for 208-240 as: Black (A phase) Red (B phase) and Blue (C phase). For 480 volt these colors will be Brown(A) Orange(B) and Yellow (C). The A,B & C phases are the line voltage conductors and are to be considered as L1,L2 and L3 when connecting to the motor. The correct connection for a low voltage (208-240V) 3 phase motor which is "Y" or "star" connected internally is: Connect The L1 (A phase) to wires # 1&7 on the motor (wire nut or split bolt all three)Connect the L2 (B phase) to wires # 2&8 Connect the L3 (C phase) to wires #3&9 Then connect motor wires # 4, 5 & 6 together Make certain you ground the motor properly!! The correct connection for a high voltage (480 V) 3 phase motor which is "Y" or star connected internally is: L1 to motor lead#1, L2 to 2, L3 to 3, then: connect motor leads 4&7 together, 5&8, and 6&9. Again, these connections are for Y connected motors. Almost all are these days as powers companies have gone to a standard delta to Y step down in voltage transforming. Again, if you're not clear on this or haven't wired large motors before, I highly recommend you hire a licensed Journeyman electician to do it. Remember, the physical wiring connections are critical and must be done well. They should be made with a brass split bolt, rubberized electrical tape and then high temp electrical tape. Motors vibrate and bad connections will come loose, causing an open or short circuit, or worst case for the motor to single phase and burn up.
Typically single phase motors go up to 10hp. Wouldn't be very efficient at about 100 amps. A 20hp 3 phase motor at 230v pulls 52 amps. The 10hp single phase 230v pulls 50 amps….
If the compressor currently has a 3-phase motor connected to a 3-phase service, then, unless there is also a single phase branch circuit outlet available at the same location,… which already has the right sizes of breakers and wiring to suit the motor's power requirement, it is not a simple matter to change the motor to a single phase type having the correct power output and motor controls. If there is no existing single-phase outlet that is suitable then: either a new single phase service would have to be installed to suit the single phase motor which is being asked about to be used as a possible replacement or it would be necessary to change the circuit breakers, wiring and outlet connections of the present 3-phase service to have the correct parts to make a single phase service that would suit the single phase motor which is being asked about to be used as a possible replacement. As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed. Before you do any work yourself, on electrical circuits, equipment or appliances, always use a test meter to ensure the circuit is, in fact, de-energized. IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB SAFELY AND COMPETENTLY REFER THIS WORK TO QUALIFIED PROFESSIONALS.
What would be the horse power required in a 3-phase motor to replace a .5 horsepower single phase motor.?
You still need the same horsepower. The advantage of the three-phase motor is that it will draw lower current.
Yes, my dad worked with motors for many years and did this regularly.
mainly due to undervoltage.
Probably not. The single phase three horse power motor will be much larger in physical size than its three phase counterpart, and will probably not fit.
A three phase motor will not operate on single phase. The motor will run on two phases but will not start. Motors running on just two phases is called single phasing. The line… current of the two legs will go high and it is this factor that the motor controller uses to trip the contactor to open the circuit and isolate the motor from the power source.
A 3-phase motor will not run on single-phase power or if one of the three phases is disconnected. If the motor is not running, there is no back-EMF generated in the coils, and… they draw excessive current, thus overheating.
Single phase implies an AC motor. There are different parts of a motor, and thus different parts may have burned out. Different causes for different parts - sometimes parts fa…il due to age, such as start and run capacitors. The rotor may be locked up, so no load is placed on it, but it cannot spin (so in actuality a whole lot of load is put on it), so the rotor burns up. Another cause could be too high of voltage applied to the motor, or too low voltage.
Yes BE SURE TO Check RPM 5hp at 1800 rpm needs 25hp at 3600 rpm caveat : single phase motors are bigger physically consume more power and run at higher current (73% …higher current) and take longer to get up to speed so the frame size may be different shaft size and bolt circle height of the shaft etc this is an easy task with a belt drive with the single bearing motor on some smaller compressors its impossible another possibility: small drives for 3phase motors have come down in price and may work just fine on single phase and may be cheaper than a single phase motor... can perhaps do pressure regulation by varying the speed of the motor instead of the noisy on off stop start ... fill the tank and idle speed up with demand...wont need to blow the air for the unloader soft start will increase the life of all the mechanical stuff
It sounds like there may be a partial short in one the the three motor windings. What should be done it to megger the motor. This will tell you if all three winding are not sh…orting to each other and not shorting or partial shorting to ground. If the reading is over 2 megohms to infinity then the motor is all right. Below .5 megohms (500000 ohms) the motor should be cautiously used and will probably have to go in for a rewind. If the burning is in the motors junction box then the burning could be caused by loose conections between the feeder wires and the motor winding leads.