Motor Phase Rotation?

[sparky81]

I changed out a motor yesterday. Hooked it up and it was running backwards. Nothing changed on the power side, just the motor. Am I correct in my thinking that different motors have different phase rotation? Meaning two different motors hooked up the same way, may not always have the same rotation. Is this a difference in the windings of the motor? I swapped the leads in the disconnect wich were already swapped from the last motor. They were YOB, and I put them back to BOY. Someone here said that if a motor is hooked up properly phase rotation should always be the same. I was always under the assumption that whenever you install a new motor you have a 50/50 chance of the rotation being correct. I guess I do not have a very good understanding of the theory of phase rotation. The motor was a 15hp at 480v. Not sure of the type. It was a 9 wire motor?

 

[GoldDigger]

I changed out a motor yesterday. Hooked it up and it was running backwards. Nothing changed on the power side, just the motor. Am I correct in my thinking that different motors have different phase rotation? Meaning two different motors hooked up the same way, may not always have the same rotation. Is this a difference in the windings of the motor? I swapped the leads in the disconnect wich were already swapped from the last motor. They were YOB, and I put them back to BOY. Someone here said that if a motor is hooked up properly phase rotation should always be the same. I was always under the assumption that whenever you install a new motor you have a 50/50 chance of the rotation being correct. I guess I do not have a very good understanding of the theory of phase rotation. The motor was a 15hp at 480v. Not sure of the type. It was a 9 wire motor?

For exactly the same motor, the same L1, L2, L3 connections should produce the same rotation. For similar motors, the standard direction of rotation may bw CW or COW. and that may be viewed from the motor e.d or te shaft e.d

 

[sparky81]

That makes sense

That makes sense

This was a different motor than the old one.

 

[GoldDigger]

This was a different motor than the old one.

Pardon the typos in my first response. Combination of big thumbs and Ought-to-Correct on phone.
But I guess the point made it through.

Physical size, HP and mounting details are enough to get it to fit, but not necessarily rotate the same way.

 

[Smart $]

This was a different motor than the old one.

If it was manufactured to NEMA standard, it should have had the same rotation direction.

Here's a link to an older thread on the matter...

http://forums.mikeholt.com/showthread.php?t=141464

 

[texie]

I changed out a motor yesterday. Hooked it up and it was running backwards. Nothing changed on the power side, just the motor. Am I correct in my thinking that different motors have different phase rotation? Meaning two different motors hooked up the same way, may not always have the same rotation. Is this a difference in the windings of the motor? I swapped the leads in the disconnect wich were already swapped from the last motor. They were YOB, and I put them back to BOY. Someone here said that if a motor is hooked up properly phase rotation should always be the same. I was always under the assumption that whenever you install a new motor you have a 50/50 chance of the rotation being correct. I guess I do not have a very good understanding of the theory of phase rotation. The motor was a 15hp at 480v. Not sure of the type. It was a 9 wire motor?

All things being equal, it should have been the same rotation. But it is not perfect world. Maybe the old motor had been rewound and they were sloppy in the lead designations, or you think you reconnected it the same way, etc. The bottom line is you always verify, never assume. Depending on the application/driven load and size, the consequences in some cases of wrong rotation can be catastrophic.

 

[meternerd]

I changed out a motor yesterday. Hooked it up and it was running backwards. Nothing changed on the power side, just the motor. Am I correct in my thinking that different motors have different phase rotation? Meaning two different motors hooked up the same way, may not always have the same rotation. Is this a difference in the windings of the motor? I swapped the leads in the disconnect wich were already swapped from the last motor. They were YOB, and I put them back to BOY. Someone here said that if a motor is hooked up properly phase rotation should always be the same. I was always under the assumption that whenever you install a new motor you have a 50/50 chance of the rotation being correct. I guess I do not have a very good understanding of the theory of phase rotation. The motor was a 15hp at 480v. Not sure of the type. It was a 9 wire motor?

Yup. 50/50 chance but you're always wrong....or so it seems. One suggestion, though. You should not reverse rotation at the starter. It should remain BOY, left to right. Change the connections in the motor "pecker head." That way, any time you have to replace the starter and have to disconnect the wires, you'll always get them back correctly.

 

[ActionDave]

One suggestion, though. You should not reverse rotation at the starter. It should remain BOY, left to right. Change the connections in the motor "pecker head." That way, any time you have to replace the starter and have to disconnect the wires, you'll always get them back correctly.

I agree with the general concept of that "rule" but I do not follow it with a religious fervour.

 

[BAHTAH]

Motor Phase Rotation

Motor Phase Rotation

I changed out a motor yesterday. Hooked it up and it was running backwards. Nothing changed on the power side, just the motor. Am I correct in my thinking that different motors have different phase rotation? Meaning two different motors hooked up the same way, may not always have the same rotation. Is this a difference in the windings of the motor? I swapped the leads in the disconnect wich were already swapped from the last motor. They were YOB, and I put them back to BOY. Someone here said that if a motor is hooked up properly phase rotation should always be the same. I was always under the assumption that whenever you install a new motor you have a 50/50 chance of the rotation being correct. I guess I do not have a very good understanding of the theory of phase rotation. The motor was a 15hp at 480v. Not sure of the type. It was a 9 wire motor?

I think Ideal is one of the manufactures of a handy little meter that will let you test the power source rotation. The same meter will also let you check the motor rotation prior to connecting it to the power supply, letting you know which way it will rotate.

 

[meternerd]

I agree with the general concept of that "rule" but I do not follow it with a religious fervour.

Shame on you!

If you've ever hooked a pump in reverse and had the 700 foot shaft unscrew and fall to the bottom of the well, you'll know why it's a good idea. Don't ask me how I know!

 

[ActionDave]

Shame on you!

If you've ever hooked a pump in reverse and had the 700 foot shaft unscrew and fall to the bottom of the well, you'll know why it's a good idea. Don't ask me how I know!

Keeping rotation for pumps that are backed up by a portable generator is one case I was thinking of. We had to switch positions in the transfer switch to keep everything spinning appropriately.

 

[kwired]

I agree with the general concept of that "rule" but I do not follow it with a religious fervour.

Shame on you!

Same here. Rule #1 when making any kind of change or replacement is to pay attention to details of what is already there and not assume that those before you followed any such rules.

If you've ever hooked a pump in reverse and had the 700 foot shaft unscrew and fall to the bottom of the well, you'll know why it's a good idea. Don't ask me how I know!

I have hooked up many deep wells and had wrong rotation. But it is common for them to have device on them that prevents them from spinning backwards, so if you "bump" the motor and get no rotation the first time you run it that means it is the wrong direction.

 

[meternerd]

I have hooked up many deep wells and had wrong rotation. But it is common for them to have device on them that prevents them from spinning backwards, so if you "bump" the motor and get no rotation the first time you run it that means it is the wrong direction.

You are correct...most of the time, motors will have a ratchet mechanism that prevents reverse rotation so water pumped out of the well will not drain backwards from the tank back into the well from a tank when the motor stops. But, there are some that have a valving setup that causes water to flow back down the well as the motor shuts off, preventing pressure "surges" in the line as the pump shuts down. This type of installation sometimes does not use the ratchet system due to the pressure transient considerations. They depend on check valves to prevent backflow. The motor is free to turn either direction, and there is nothing to prevent reverse rotation if the motor is wired backward. Since the threads on the shaft sections are threaded to tighten in the direction of normal rotation, reverse rotation will unthread the sections and the shaft WILL come apart, dropping the pump to the bottom of the well casing. I know because it happened to me. (Not my fault, though. A contractor had reinstalled the motor after rebuilding the pump and hooked the motor backwards, then fired it up for testing and had low motor current. That's when they called me.) Rotation should always be checked BEFORE the motor is coupled to the pump. Just my humble opinion, though. Most times, revrse rotation is not a disaster. Just that sometimes it can be.

 

[ActionDave]

Rotation should always be checked BEFORE the motor is coupled to the pump. Just my humble opinion, though. Most times, revrse rotation is not a disaster. Just that sometimes it can be.

I follow this rule a bit closer. Not just for hollow shaft pumps either. Hydraulic pumps can make a horrible mess or worse if you run them backwards. Yuck.:rant:

 

[kwired]

You are correct...most of the time, motors will have a ratchet mechanism that prevents reverse rotation so water pumped out of the well will not drain backwards from the tank back into the well from a tank when the motor stops. But, there are some that have a valving setup that causes water to flow back down the well as the motor shuts off, preventing pressure "surges" in the line as the pump shuts down. This type of installation sometimes does not use the ratchet system due to the pressure transient considerations. They depend on check valves to prevent backflow. The motor is free to turn either direction, and there is nothing to prevent reverse rotation if the motor is wired backward. Since the threads on the shaft sections are threaded to tighten in the direction of normal rotation, reverse rotation will unthread the sections and the shaft WILL come apart, dropping the pump to the bottom of the well casing. I know because it happened to me. (Not my fault, though. A contractor had reinstalled the motor after rebuilding the pump and hooked the motor backwards, then fired it up for testing and had low motor current. That's when they called me.) Rotation should always be checked BEFORE the motor is coupled to the pump. Just my humble opinion, though. Most times, revrse rotation is not a disaster. Just that sometimes it can be.

You lift the 100 hp hollowshaft motor off the shaft for me while I check rotation:thumbsup:

Irrigation wells here all have mechanical device to prevent reverse rotation. Backflow is prevented by check valves. No check valve and water is going to fall back down the well when the pump stops. The pump impeller is not tight enough against the housing to prevent water from back flowing.

 

[meternerd]

You lift the 100 hp hollowshaft motor off the shaft for me while I check rotation:thumbsup:

Irrigation wells here all have mechanical device to prevent reverse rotation. Backflow is prevented by check valves. No check valve and water is going to fall back down the well when the pump stops. The pump impeller is not tight enough against the housing to prevent water from back flowing.

You lift the middle, and I'll lift both ends......

We do use hollow shaft motors up to 500 HP, but they have couplings on top. Some have ratchets and others do not. We always bump them for rotation before we couple 'em. Even the 100 HP+ booster pumps we use to pump from one tank elevation to the next have ceramic seals which will be instantly destroyed if rotation is reversed. Big bucks if we screw one up, so we're pretty careful. Now, back when I was a young guy working nuclear, we had 13,800 volt, 9000 HP motors that did have ratchets, but you sure didn't want to bump 'em for rotation. We used rotation testers and used a 12 ft bar to turn 'em enough to get a rotation reading. Too much work for a geezer like me.

 

[kwired]

You lift the middle, and I'll lift both ends......

We do use hollow shaft motors up to 500 HP, but they have couplings on top. Some have ratchets and others do not. We always bump them for rotation before we couple 'em. Even the 100 HP+ booster pumps we use to pump from one tank elevation to the next have ceramic seals which will be instantly destroyed if rotation is reversed. Big bucks if we screw one up, so we're pretty careful. Now, back when I was a young guy working nuclear, we had 13,800 volt, 9000 HP motors that did have ratchets, but you sure didn't want to bump 'em for rotation. We used rotation testers and used a 12 ft bar to turn 'em enough to get a rotation reading. Too much work for a geezer like me.

Your applications were likely different than what I commonly run into. Well company installs the well and puts the motor on before I even have seen the installation most of the time. I do not install the motor and have no reason to have a crane to lift them as I rarely have the need to. When connecting for the first time I always bump the motor, you can tell immediately if it has correct rotation or not, and doesn't hurt anything if it is wrong.

 

[meternerd]

Your applications were likely different than what I commonly run into. Well company installs the well and puts the motor on before I even have seen the installation most of the time. I do not install the motor and have no reason to have a crane to lift them as I rarely have the need to. When connecting for the first time I always bump the motor, you can tell immediately if it has correct rotation or not, and doesn't hurt anything if it is wrong.

Just one little story. We installed a new 500HP 480V motor and decoupling it would have been a real hassle. Contractor installed it and we wired it. Had an anti-reversing ratchet. So we figured, like you, if it was backward, it wouldn't hurt anything. Bumped it for rotation and the breaker tripped instantly. Motor slowly spun in the correct direction. Checked everything out...no grounds, correct breaker setting, voltage good, soft-start showed no codes, etc. We tried it again with the same result. We finally figured out that rotation WAS backward, and the motor was bouncing off the ratchet and coasting in the right direction. Reversed rotation and all was well. Felt kinda stupid afterwards.

 

[kwired]

Just one little story. We installed a new 500HP 480V motor and decoupling it would have been a real hassle. Contractor installed it and we wired it. Had an anti-reversing ratchet. So we figured, like you, if it was backward, it wouldn't hurt anything. Bumped it for rotation and the breaker tripped instantly. Motor slowly spun in the correct direction. Checked everything out...no grounds, correct breaker setting, voltage good, soft-start showed no codes, etc. We tried it again with the same result. We finally figured out that rotation WAS backward, and the motor was bouncing off the ratchet and coasting in the right direction. Reversed rotation and all was well. Felt kinda stupid afterwards.

If it is on a soft starter I would think that would make that less likely to happen, but I am not going to tell you it did not happen either.

 

[tes]

Why take a chance? Eliminate the guesswork. We use the "IDEAL" # 61-521, "Phase / Motor Rotation / Tester.
Connect it to the energized motor starter output and it gives you direction of rotation. Connect it to the motor T-Leads, rotate the motor in the correct direction, compare the results. Connect the motor for the correct rotation, and your done.