when reversing a 3-phase motor
when reversing a 3-phase motor
(OP)
When reversing rotation of a 3-phase motor. Does it matter wich 2 wires are reversed? I was told any 2. But after what Iv'e learned here and in books , it states A B C or
C B A. So if you reversed switching A&B OR C&B could this throw off the timing of the motor? I am new at this and when I was trained it wasn't by "professionals". So sorry in advanced if this was a dumb question. thanx
C B A. So if you reversed switching A&B OR C&B could this throw off the timing of the motor? I am new at this and when I was trained it wasn't by "professionals". So sorry in advanced if this was a dumb question. thanx





RE: when reversing a 3-phase motor
RE: when reversing a 3-phase motor
RE: when reversing a 3-phase motor
Your question is not "dumb" is a perfectly valid question, you were told right, any 2 phases can be exchanged to reverse rotation in a 3 ph. motor, no harm will be done to it, but be careful because the load it drives might not tolerate reversal of rotation like a centrifugal compressor as you know.
What is hot to you? A class H insulated motor can be very hot to the touch and it is running ok! Can you explain your last statement?
RE: when reversing a 3-phase motor
http://www.franklin-electric.com/Manual/AIM_33.htm
RE: when reversing a 3-phase motor
RE: when reversing a 3-phase motor
How that applies to your situation is that in the process of reversing your motor, you may aggravate any system unbalance conditions that were corrected in the original phase sequencing, so your motors could conceivably run hotter in reverse. This however would only apply to being hooked up to an open delta utility source. For any other service connection, OperaHouse is absolutely correct. And as far as I know, other countries do not use open delta configurations, however maybe some other members can shed light on that.
corrosivo has a good point as well. How hot is hot? It's all relative. Many people assume that if the frame is too hot to leave your hand on it, it is in trouble. That's a poor test method, because most insulation designs will allow temperatures far in excess of what humans can tolerate.
Unless you are considering very large specially made medium voltage motors, I would not worry about what brupp mentioned. 99.999999% of all 3 phase motors are designed to cool themselves in either direction. The arrow on the case is often there just to show the normal direction of rotation when A-B-C phase rotation is applied or is applied after installation to indicate proper rotation for future service personnel.
"Venditori de oleum-vipera non vigere excordis populi"
RE: when reversing a 3-phase motor
p.s.
this will be the third time I've tried to post this hopefully this time it will go through.
RE: when reversing a 3-phase motor
It might just be that the motors are heavily loaded right below the nameplate rating or even pushing service factor amps. Do an amp check or otherwise check the loading.
I have encountered a few machines that required a larger motor such as an alledgedly 3 horsepower pump that was really 3.5 horsepower. Somebody at the manufacturer ( Dunham-Bush ) thought that they could drop a decimal point and get away with it. More details about the problem in another thread.
Mike Cole, mc5w@earthlink.net