AboutWill Expertise Three phase electic motors, controls and related problems or failures, three phase motor installation issues, performance issues, connections, data and duty cycle information. All other electic motors. Specialty motors, repair concerns, performance concerns, obsolete motors and solutions. Other specialty equipment issues. Lost nameplate data and identification, lost connection data.
Also DC motors of all types.
See my profile under Home/electrical at this site
Experience 30 plus years in the electrical motor and apparatus repair industry. VP level management of repair facilities, current owner of my own specialty repair and consulting firm.
Organizations EASA, IBEW [retired], other specialty organizatons, Lubrication, Vibration EDI, Triboelectric Councils
Publications Currently fielding concerns at this site under "Home Electrical"
Education/Credentials 4 year technical, College level specific courses, EASA repair courses, vibration analysis electronic and electrical trade school.
Expert: Will Date: 5/17/2008 Subject: Reversing 3 phase motor
Question QUESTION: I would like to have the capability of reversing on demand a 7.5 hp 220V 3 phase motor. Is there a drum switch that can handle this amperage, or is there some other way to be able to switch direction of this motor?
ANSWER: Ken,
A reversing capable motor starter would be best, you could consider a frequency drive, [variable speed capable] and reversing by either keypad or remote.
You have 7.5 HP and at 230 volt that is about 23 to 25 amps, size 1 Nema starter. See below for some examples.
Remember the code letter on your motor will determine the max number of starts per hour, generally speaking around 25. You need to find out the code letter and check with me or an EASA manual for the allowable starts and intervals between. You are not going to instant reverse are you?
If you are, I would go back to the frequency drive idea, the modern frequency drive can control speed, reverse, dynamic brake, slow before reversing, overload protect all in one box, simple to program or operate manually.
The drum switch will be hard to find and the arcing between directions can be an issue, it depends on what your application is.
If you go the frequency drive route, give me a reply and some more details and I will price one out for you.
QUESTION: Thanks for the information. The use of for an industrial belt grinder. The motor is a Baldor 17.4 amp Code M Des A Class F continuos duty motor. I will not be instantly reversing. I looked into some reversible magnetic starters. On these switches what is the users process to place the starter to engage the reverse circuit.
Thanks again for all of your help,
Answer You will be fine no instant reversing, and the rest is fine too, I guess I am not sure what you mean by the user's process?
If you use a reversing starter, you can pick one with the throw switch on the box, mount a switch remote, lots of choices, basically all you are doing is reversing two of the three power leads, so it is not a complex operation.
When you get up over 15 amps finding a drum switch is tough, the amps making and breaking burn the contacts off pretty fast, if you use a starter, the control circuit does the work, and eliminates the arcing.
So i am not quite sure what I should answer, but you will find that with the appropriate starter, it is not a big deal, and I am here to help walk you step by step if needed.
On a frequency drive there is nothing more than three leads in, three out, and a keypad, if there is not enough room to place the drive, you can wire on a remote to the box and mount it anywhere.
I am a little dense right now, got a lot going on, so excuse me if I didn't get exactly what you need, I assure you this is done all the time but mostly with either a starter or drive, and not much fuss.
Let me know what I didn't understand and we will get you fixed up.
