2 HP Motor pulling 80 amps!

inrush starting current?

If the motor is drawing 80A it should not do it for very long before either the 30A CB or the overloads trip. Unless ....

The chattering relays imply low voltage but also the possibility that the control relays may be miswired - either a factory error or (more likely) a field fix to "solve" the "problem". Having been on both ends of problems like this (both as technician and engineer/designer) I would not rule out anything - including wrong voltage altogether. I also know from sad experiance that you are not getting all of the information available - the electrician is only seeing what appears to be relevant to him/her - and I really get the "willy's" when it is reported that they reduced the branch circuit length by 300 feet! So imagine this scenario: initial low voltage on startup due to exsessive voltage drop and subsequent inability to reach full RPM resulting in high current and tripping of O/L or CB. Attempted fix by "correcting" a "wiring error" in the controls - also a rerouting of the branch circuit thrown in for good measure.

Try this guess: With just an "electrical" interlock between the reversing contactors and a miswire creating the logic version of a "buzzer" you could have a condition that would produce the symptoms described: Chattering relays, high current and a stressed motor as it alternated forward and reverse without ever reaching full RPM. Because the circuit for the motor may actually OPEN momentarily it may give the thermals and circuit breaker time to "cool" a bit thereby delaying their trip and giving the observer time to measure current and listen to a motor go schizophrenic. Finally, depending on the type of meter the electrician is using, the 80A data point is more than likely an average value (RMS) and not peak.

Would appreciate feedback once you do solve it - "the rest of the story" so to speak..

Often these things have a tendency of just "going away" especially when the installer discovers the error was his..

The information you have given is insufficient to give any advice.First what is the Type of Motor AC or DC ?What is the rated voltage of the motor? Is it a single phase 110 volts or 22o volts motor or 3 phase 220volts or 440 volts motor ? It might be that the motor is of 110 volts and is now connected to 220 volts supply .You can check the current drawn with help of tong Tester .Why the overload is not tripping if the motor is drawing 80 Amps.If the motor is actually drawing 80 amps the motor should have burned by this time since it is only rated 20 amps.Better consult a competent Engineer locally who can sort out the problem .

if the motor overdraws like that, its a short circuit and a fire hazard. shorted windings can create a loud buzz. bad bearings can also allow the rotor to chatter aginst field windings/plates leading to short circuits and loud noise.

thats assuming the input wiring is correct, esp in 3phase, cross those wires up and you will need a new motor soon[a few seconds] in 220 and 3 phase especially.. wire colors are very important, when the wrong cables are used and one color is substituted for another, then next electrician can be led astray... start with a proper supply cable,

replace that motor immediately, much cheaper than the consequences.

jstacat

Well, those are 3 pole contactors but a 1 pole overload relay, so most likely it's a 1 phase motor, and the 20A rating at 2HP would put it at being a 120V motor. With that big of a 120V motor, voltage drop is a big problem. Whoever made that decision was not thinking well, I would have at least gone 240V if you had to stick with 1 phase power. Anyway though, you have it now...

80A is not an unusual amount of starting current for a motor that big. Technically, it can be as high as 600% of FLC, so in this case 120A worst case; 80A (400%) then looks OK as far as that goes. So like the others have said, you need to give more information.

• Does the motor really start turning or just sit there making noise when you try?
• How and when did you measure the 80A?
• Was that while it was running or just when it started?
• Did your meter have a "peak hold" display feature so that it only shows the highest amount, regardless of how long it was there?
• Does the Overload Relay trip out or a breaker trip?
• How long is the total wire run now? You mentioned that he reduced it BY 300ft. Was it a lot longer than that?

Possible issues:

1. The starting capacitor is now bad on the motor (may have been damaged by the earlier low voltage problems) so it fails to start, stays in locked rotor and starts to burn up.
2. The electrician has still undersized the conductors. For a motor circuit of that size, he would have to have a minimum of #10 wire, much larger if the total run distance from the breaker panel is more than about 25ft.
3. Buzzing of the contactors made them burn the contacts, but if they were not replaced because they appeared to work when tested, now they failed a short time later from the stress.
4. Those contactors are not likely "reversing" in that they have a mechanical interlock in addition to some electrical interlocks. The danger there is that electrical interlocks can fail, allowing your controls to try to run both contactors at one or chatter back and forth really fast. Bad bad bad.

I suggest you hire someone more competent to look at it who will discuss your situation without the doublespeak. Keep in mind that the vast majority of "electricians" work on residential installations and have no clue about motor controls etc., yet few will admit it. As around for recommendations on a good INDUSTRIAL electrician or contact a motor rewind shop to see if they have someone who can come out and check into it.

Hi Jref you seem a good analyst. Where in CA you locate and are you asociated with consultancy co?

that motor i guess a 3 phase because of the reverse word stated and 80 amps for 2hp motor very high.we had a 2hp motor 220 volts 3 phase with amps drawn when running equals to 6 amps only and as exprience when using 380-440 volts it will be on lesser current.by the way ur problem is that such a large noice.take apart the motor with the gear box.run the motor only,observe the current and rhe noise,if no noise and current normal,problem maybe on the gearbox,open and check mechanical elements such as worn bearings or gear teeth off already,same for motor ,check the shaft play by manually push-pull method downward-upward or forward-backward,if there is play.replace worn out bearings.

motor will not run longer if short circuited,also check loose electrical connection and tighten it as well as clean and check for correct phasing.thanx

Replying to a comment here, while adding to #4 above; the contactors are 3-pole which can be used for reversing both single and 3-phase motors. Single-phase get reversed by switching the relationship between one end of the "Start" winding (which tells the motor which direction to spin) and the line. Capacitor-start and split-phase motors (1-phase motors) have a switch (either centifugally operated off the end of the shaft) or electronic, to kick-out the start winding after the motor reaches a percentage of full speed. If the switch is stuck (they will "weld-together" after time, under the right conditions) the motor will be pulling very nearly locked-rotor amps, growling severely, and unable to achieve full speed. You left out that critical parameter of the motor in your explanation of the problem; single or three phase.

Wishing U success ~

Sir, From what i know on your problem is a simple troubleshooting .

1. Check how knowlegeable your ET can analysed the problem.

2. Check all the wiring connections. may be there's a loose wire on the circuit.

3. Check the two contactors coil and contacts.

4. Then isolate the motor for self test in different power supply. Short circuit armature will create noise and runs roughly and create noise. Change the motor.

5. 80 amp. is too much for rated 20 amp motor.

So as to not mislead the owner of the problem, I believe it has been established that we're facing an AC motor problem. Unless the odds have flip-flopped from about 10¹⁰⁰⁰ in favor of this, there is no armature to be shorted, and the likelihood of a shorted squirrel cage rotor //the obvious scenario\\ is about, suffice to say, the last thing to expect. As far as a loose wire on one of the relays - if it's a control wire on one of the solenoids, then the chattering would likely manifest, but would NOT be causing the continuous high current draw. A loose wire on either of the line-sides of a relay would cause the high resistance wire (portion of the circuit) to fry //usually right at the terminal\\ and the resulting smoke would divulge the answer to the problem immediately. Test the motor using a "cheater cord" for power (fuse protected of course) under no-load conditions. By eliminating the controller you will isolate the problem easily. Guarantee good for 60-days

could the high amps be starting surge along with voltage drop /

FLA 20A

Is the 80A starting current ?

Reduced the run by 300 ft at what voltage 110 vac- 6o HZ.? What is the length of run now ( Resistance of wire for wire size comes to mind .)

Has the motor been decoupled from the gear box? draw while decoupled? OK 80A can be present with wrong ols or ols fried closed.

Now motor making sound of trying to pull apart running or stalled?

Decouple from gear box and start from there !

*0 A.

I had similar problem 3 phase 600 vac motor 0.5 Hp drawing 27A blowing 2 fuses not burnt out bad ol on 1 phase current after replacing ol 0.47- 4 A stall on a conveyor drive system Note conveyor lots of stop/ go some reversing.......