Three phase motor connections

Hello all

Please can anyone tell me what the two extra connections in the terminal box of an Aluminium Brooks Crompton 1.1 KW three phase motor A- DA90SA 4-B3 PTO might be for?there the usual six phase connections buthere are two others with much thinner single white wires connected to them which appear to be connected to the stator windings.The phase connections have the markings U V and W but the extras have no markings that I can see.I aquired this motor to make a rotary converter as a result of some bin diving at my local scrap merchant.

Thanks to anyone who can enlighten me.

Paul

Thermistor.....

But what do I know....?? 

Edited By John Rudd on 28/06/2016 19:22:55

Hi Paul, The 'PTO' is thermostat control to stop the motor being overloaded. 'PTC' is for a thermistor control circuit. I guess it depends how hard it's going to be worked and whether you want to add this safety feature. Brooks Crompton have quit a bit info on there web sites.....DDT

Thank you John and DDT, This willl be used as an idler motor so only run on light load via a capacitor generated third leg. The motor was scrapped because of an earth leak but it was full of water, I'm hoping that careful drying will restore it, the motor appears to have not been used and only tested prior to installation.No magic smoke smell or discoloration and all three phases have equal resistance. Presumabley the contacts go to a relay/switch outside the motor for a legit installation.

Thanks again to both of you

Hi Paul, Regarding your testing of the motor, if you have one great, if you haven't, borrow a mega to check the insulation between the windings and to the casing. Better this way than having the magic smoke appear, because it never wants to go back !..........DDT

Hello Paul, The two wires will be for a 'Klixon' type of over-temperature switch. These are usually required for speed control at full torque, as the cooling fan is only shaft mounted. The alternative would be to de-rate the motor (for torque) for low speed. Not a bother for you, as you will only run it at full speed.

An alternative answer:- We had many motors that had the PTC embedded in the windings. The nominal resistance was 600 ohms. perhaps as many as 10% of them failed by the thermistor going O/C due to the temperature cycling of the windings crushing the poor little thing. So the motors were initially rewound with new thermistors. Later we just wrapped the motors in "Fire Wire" . This is a special two core cable that goes short circuit at 70 degrees C.

Perhaps your thermistors are open circuit and there is nothing else wrong with the motor?

Frank