ECN Forum Forums Technical Discussion Electrical Theory and Applications Low / High speed 3 phase motor problem

I am a small electrcial contractor who works on some 3 phase items here and there, I feel confident in what I know about it, so here is my problem... We are hooking up a resturant exhaust fan , this is a 3 ph 120/208 2 speed unit. It has 6 wires on the motor listed T1-T6 . It came with a small junky little speed control switch that has the options of ( low off high ). we ran all our wires to it and checked rotary field with our tester before any power went to motor. it works fine on low speed but when we switch it to high it will run about 1 minute and blow the fuse protecting L3 line. we have used time delay and instant fuses all at 20 amps. the motor gets real hot and when you turn it off you can smell it cooking. We have used a continuy meter all of our wire's to make sure nothing is crossed, it isnt. so out of desperation we bypassed the speed control and hooked up direct and ran the motor at low speed and it works perfect, switched around the power leads and motor taps to make it run at high speed , same thing, gets hot and smokes. this is a BRAND NEW unit, can motor be bad like this from the factory? I have never ran across this before ever , and I have checked out my wiring 2 times , and always used a rotation meter before shooting power to the motor. I am lost , any help pleaseeeeeee???

1 more thing, it is a 3 1/2 hp motor and it is wired with 12 guage, the breaker box is 29 feet from this unit.

Are you sure that you are making the correct connections and have the correct controller?
There are a number of different two speed setups and they wire different. How are the leads tagged and how are you connecting them?
Don(resqcapt19)

motor label wiring is listed as


low speed high speed

t1---- line 1 ------t6
t2---- line 2 ------t4
t3---- line 3 ------t5


t4---- t1-t2-t3 tied together
t5----
t6----

going with this when we hook up for low speed we have connected t1 to line 1, t2 to line 2 , t3 to line 3. leaving t4,t5,t6 not connected to anything.

when we hook up for high speed we tied t6 to line 1, t4 to line 2, t5 to line 3 and joining t1,t2,t3 together with a wirenut, the controller we have is a device that lookes like a fork blades that connect the motor together just as we do when we bypass the controller and hook direct, we have 6 motor leads going to 6 leads on the controller......

My reference material says this:
Low speed--line 1 to 2, line 2 to 3, line 3 to 1, and 4,5,6 open;
High speed--line 1 to 4, line 2 to 5, line 3 to 6, 1,2,3 together.

http://www.marathonelectric.com/motors/dxf/pdf/EE7322.PDF


not for this motor...........

the controller is a drum type with forks in it that switch the connection's depending on the speed or if it is turned off..... I am just going to call mfg. monday and ask for a replacement, I have hooked up 4 of these in the last couple years and never had a problem, I am real confident that the motor was bad from the beginning.