#teachme Going to shed some light on the term single phasing, and please, if I miss anything do add it in the comments section. On the induction motors we mostly work on, single phasing is when one of the phases of a three phase circuit is opened leaving the remaining current to be carried on two phases. With the two phases remaining it is effectively powering a three phase circuit like a single phase circuit, hence single phasing. Except we are not looking to accomplish this on a three phase system🙅‍♂️ With a three phase motor in operation, losing a phase will keep the motor operating if no protection devices are in place. The excess current carried across the two remaining phases also causes excess heat. That heat is then carried through the stator winding, breaking down the winding insulation, fast. Winding insulation is not meant to handle the excess heat which is why we sometimes have thermal overloads or other protective devices to prevent winding damage any further. The effect of single phasing on a stopped motor would effectively carry locked rotor across your remaining two phases and prevent the torque necessary to start the motor. A motor attempting to start will effectively stall and produce a noticeable audible sound. This will quickly lead to further insulation from the windings breaking down and eventual thermal overload trip or fuses being blown. Measuring potential on a single phasing condition will render a low voltage from line side to ground on one of your phases only. If your having problems with thermal overloads tripping, using a Megaohmmeter is a good way to ensure your customer their compressor still has some life, or it has 💩 the 🛌. Lastly, contactor maintenance with regards to carbon tracking. Gary @HVAC Know It All has a great article on this that you can check out on this link below 👇 It is also one of the many causes that can lead to single phasing of a motor. https://www.hvacknowitall.com/blogs/blog/171143-carbon-tracking-explained#.YG_BfiX3YlQ This is very important during your maintenances as these cheap little “switches” controlling very expensive components. So take that extra 5 minutes to be a better tech and gibe your starting devices a good once through and a brush clean during those maintenance inspections👍 #hvac #hvacr #singlephasing

Posted by hvacr_mech_life at 2021-04-09 03:01:59 UTC