What is Common, Start and Run?

hey thanks for watching in this video i want to do a quick introduction of common start and run and what that means for folks who may be newer to the trade or maybe struggle to understand it first off when we talk about common start and run we're talking about single-phase motors which specifically means that we're not using three-phase power we're not talking about ecm motors that stands for electronically commutated motors we're specifically talking about single phase something called a psc motor or a permanent split capacitor motor and the reason why we're talking about that is because it's such a common motor in our trade when we say common start and run we're talking about three terminals or connection points whether they be wires or terminals to a motor we see these on compressors and condenser fans most commonly and we see them in older blower motors nowadays more blower motors are going to that ecm style design and again this is residential and light commercial is where you're primarily going to see this when you see a diagram like this those little squiggly lines are representing windings that are in the stator of the motor keep in mind that that a motor is essentially a gigantic rotating electromagnet that stator on the outside generates this rotating electromagnetic field that spins the motor around your main winding is your runwinding your runwinding is the winding that does the majority of the work for most of the operational time but then you have this auxiliary winding that we call a start winding which helps get the motor started but then it also assists with motor efficiency and directional force so that's what that start winding is for but on a psc it's kind of a misnomer because it's not just in while it's starting it's always in the circuit and especially if we're not using a start capacitor or a hard start kit really your run capacitor is helping with starting and running and there's really nothing else going on there it's just it's operating in the same way when it starts and when it runs there's no relays there's nothing taking it out of the circuit it's just in there all the time your run winding is connected to one side of power your common terminal is connected to another side of power and your start winding is connected in series with your run capacitor and again this is on a psc single phase motor that we're talking about here specifically so you go outside to your regular old compressor on your house that's generally going to be a single phase psc motor with a run capacitor in place there are three terminals but there are only two windings there's only the start winding and the run winding there's the common terminal the common terminal also has an internal overload that's connected in behind it so that that way if the motor overheats it shuts the unit off and so that breaks that circuit i'm going to quick throw up a illustration that shows you kind of the way we represent this so you can see the three terminals on a compressor but then back behind that you see you have the two windings and then you also have that internal overload that breaks the connection in between those two good information to know just good general knowledge is that your highest resistance measurement between any terminals are going to be between your start and run your lowest is going to be between run and common and then start in common will be the middle one you're not going to know exactly what those resistance numbers will be unless you have specific data from that manufacturer which you can get from something like the koplan mobile app to tell you what it should be not generally a super useful test to do in the field but we do know that all of these terminals and all of these windings should be connected to one another and they should not be connected to ground and so that's one thing that we do check for regularly is whether or not the windings are grounded or whether they have a path to ground using an ohm meter measuring that resistance on your standard pse motor keep in mind the run winding does the majority of the work the start winding is there to kind of get it running in the right direction and to help with that and it's in series with your run capacitor also just a quick tip to keep in mind when you connect your start winding to a dual capacitor you're going to connect that to the herm terminal with the c terminal on a dual run capacitor the typical run capacitors we see on a lot of units that does not connect to the c terminal on the compressor it connects to the same side of power that run connects to because remember common and run are the two that are connected to power and so a lot of people will think well it says c on it that should be c on the compressor and the capacitor and that is not true those are actually opposite legs of incoming power that those connect to so that's just a quick tip for the field something to watch out for so keep in mind highest resistance is going to be between start and run lowest resistance between run and common and then start in common one left that's the one that's in the middle on this image that we show here those are just examples they're not always going to be that those numbers you have to know what the specific measurements will be for your specific motor that you're working on and if you find that there is a path measuring with an ohmmeter if you take an ohmmeter and you measure between start and run and you find that you have a good path and then you measure from common to start and common to run and you have none that's an indication that that thermal overload is open as you can see there if that thermal overload is open you're not going to have a measurement as far as the path goes to that c terminal that's some basics common start and run we're going to talk about hard start kits we're going to talk about three-phase motors in some upcoming videos that's the basics of common start and run or cs and r as it relates to single phase psc motors thanks for watching we'll catch you in the next video thanks for watching our video if you enjoyed it and got something out of it if you wouldn't mind hitting the thumbs up button to like the video subscribe to the channel and click the notifications bell to be notified when new videos come out hvac school is far more than a youtube channel you can find out more by going to hvacrschool.com which is our website and hub for all of our content including tech tips videos podcasts and so much more you can also subscribe to the podcast on any podcast app of your choosing you can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching

Channel: HVAC School

Views: 188,005

Keywords: hvac, hvac school, Start and Run, start and run hvac, capacitor, compressor, single phase compressor, terminals, compressor terminals, compressor wiring, common start run diagram, start run, how to, hvac training, hvac tech, run capacitor, fieldpiece, psc motor, single phase psc motor, compressor winding, single phase motor, common start run, common, start, run, ohm meter, multimeter, digital multimeter, start winding, run winding, hvac compressor, hvac capacitor, Bryan orr

Id: g2ADgrUhb7Y

Length: 6min 10sec (370 seconds)

Published: Mon Nov 23 2020