Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
Is this a real thing, guess actually called phase rotation, that the electrician needs to do regarding motors? Is it a long process?
Motor "Bumping"
- Thread starter Alwayslearningelec
- Start date
ptonsparky
Tom
- Occupation
- EC - retired
Yes, you briefly start a motor to confirm proper rotation. Very short. YMMV because some equipment may not tolerate reverse operation.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The bump is literally one second. If the rotation is backwards then you would need to swap two leads. This can be a lengthy process depending on what's involved to make the swap. Typically it doesn't take very long.
MD Automation
Senior Member
- Location
- Maryland
- Occupation
- Engineer
Here is a quick example from when I was helping commission large mail sorting machines...
This machine had lots of expensive vacuum pumps that needed a specific direction of rotation. Such machines are commonly marked with a curved arrow on the bell (fan) end of the motor. Somebody would power the motor on for 1 second, like Infinity said, while somebody else was down inside a cabinet with a flashlight watching the fan end of the motor to see if it was spinning like the arrow indicated.
If something like these pumps ran the wrong way for second, nothing terrible would happen. The bump is typically so quick it never even gets to full speed, you just want to get the motor shaft moving to watch which direction it went.
If you are working on a machine where the motor powers something that absolutely cannot be driven backwards without damage, then you will need to uncouple the motor from the machine (like remove belts from a pulley), then bump the motor.
This machine had lots of expensive vacuum pumps that needed a specific direction of rotation. Such machines are commonly marked with a curved arrow on the bell (fan) end of the motor. Somebody would power the motor on for 1 second, like Infinity said, while somebody else was down inside a cabinet with a flashlight watching the fan end of the motor to see if it was spinning like the arrow indicated.
If something like these pumps ran the wrong way for second, nothing terrible would happen. The bump is typically so quick it never even gets to full speed, you just want to get the motor shaft moving to watch which direction it went.
If you are working on a machine where the motor powers something that absolutely cannot be driven backwards without damage, then you will need to uncouple the motor from the machine (like remove belts from a pulley), then bump the motor.
Years ago we had maybe six 5 HP pit pumps that had screwed on impellers where when we replaced a bad motor would C camp one leg of motor to platform then give it a quick on off to check for proper rotation. If pump ran in the wrong direction impeller would unscrew.Was the only piece of equipment that would cause a problem if motor were to be ran a second in the wrong direction that I came across.
Joethemechanic
Senior Member
- Location
- Hazleton Pa
- Occupation
- Electro-Mechanical Technician. Industrial machinery
I always used to do it by very briefly pushing the contactor in with my finger. But now that makes safety guys nervous