Ladder Diagram Basics #3 (2 Wire & 3 Wire Motor Control Circuit)

alright guys let's go over some basic wiring for motor control in this video we're going to do the 2 wire and the 3 wire control for contactors for a three-phase motor control so the first thing we're going to do is the the 2 wire control with this guy we're going to find that there is obviously two wires in the pipe and possibly a bonding conductor with this one or not one of the terms that corresponds to the 2 wire control is low voltage release so the reason why this guy is called low voltage release is this is often the wiring for a pump or for you know a fan or HVAC unit or something where in this case on this diagram we have a float switch that when it closes it turns on the pump so if this contact was closed so it's calling for the pump to be on and all of a sudden we lost power well then the coil would kick it and then we would lose power to the motor so these three contacts would open and we would lose power to the motor once power was restored to the circuit and that normally closed contact on the float switch was still being maintained closed well then we have power going to the coil that will re-energize those contacts closing them and allowing current to go to the three-phase motor so to wire control is for if you lose power the motor is going to kick off when power is restored all that's happened is that the coil has just released once the power is restored the coil will turn back on energized and close those contacts and re-energize the three-phase motor if we look at the 3 wire control it's going to be called low voltage protection and that you're going to have to press a push button or turn on a key switch in order for that motor to turn back on now why would you want to run around the whole building trying to turn on all the pumps and all of HVAC units on a loss of power doesn't make sense so we need to have something like a 2 water control so it when power is lost the motor turns off when the power goes back on the building everything turns back on this is fed by a circuit like this now we're going to take this circuit right here we're going to bring it over to the next page and then we're going to do some wiring based off of there so what we'll do is we'll draw in that diagram below so this guy is a normally open float switch and normally open because gravity would act on that to pull it down now we can do the float switch first that's a better practice to do that the overload as the first thing in your circuit now the overload is a normally closed contact right and that guy is right here it's right beside the heaters one two three heaters and they're just there to protect the conductors of the three-phase motor all the current goes through these heaters heats them up and then if any of them heat up to a certain point this contact is going to open and if this contact opens then we no longer have power to our clothes will drawn or coil here and line two or neutral depending on which voltage that we're working with if this was 120 volts as the source for our controls this would be line one this would be neutral if we had two eight or six hundred then we were grabbing to the power from any two line connectors so this would be line one and this would be line two so that's what we'll do for this diagram here now we'll label out each of these conductors one two is the return we go through that over the contacts we have a new wire number then we go through another component being they norm the open float switch so then we got four wires here okay so let's go through the take that diagram and now wire up our wiring diagram above looks like first thing we're doing is we're going to be overload so we'll pick that up off of line one and this guy's done good practice to check off each wire as you put it in there you don't miss anything from there we're going out to the field to the normal to open contact for a float switch we're coming over here pickin up the overload PD that guy's done okay if we wanted to put our conductors here this is one one this conductor would be labeled three and this guy is labeled three as well okay from there we're now going to the coil so we're going to pick up our coil here from a normally open float switch see if I can reach this knot takes out the holding alright with that this guy comes down fix like I have beauty there is our coil this is done last thing we need to do in this case is go to line two over these guys pick up line two and excellent we're done that's all it is okay the conductor here would be for this guy would be four right and then our return is going to be labeled conductor number two inside the pipe how many wires will be gone well it's to our control so we're going to have two conductors in the pipe and a bond wire it to wire has two connectors on the pipe three wire is going to have three conductors in the paper next one three wire control we've got our ladder diagram we've got our wiring diagram and we've got a pictorial of what's going on here okay so what we're going to do is we're going to take this diagram here for the ladder diagram transfer it over to the page with the components with the the starter here so here's some you know basic diagrams there for the three wire control this one here it says it's the three wire but they don't have the the holding contact the three water makes use of the holding contact across the start there okay again another diagram of the three water control I like to put the the stop first and then the stirrup in this case they've put the start and then the stop push button and then they've got I've actually got their overload in a funky place in between the motor contactor and their push buttons it doesn't really matter it's in series with the coil but it's usually the first component in the circuit okay let's take a look at this one now so we'll do our diagram for the three wire up here line one we're going to do our stop push button here stop is the normally closed then we're going to do our start start is the normally open then we're going to go to the coil I forgot the overload so let's drop the overload in there now all the textbooks have this guy at the end alright so what a coil is there or we could put in an EM there for motor contactor and then we've got line two so yeah all all the textbooks have the overload over here but by rights the overload should be the first thing in the circuit this as John is still a two wire control the key to making this guy a three wire controls to put that holding contact across the normally open switch now if we didn't have that overload there then labeling that's it we could just go one two three all right so normally this guy right here is labeled two and three on the starter the reason for that is that if that overload wasn't there is the first component in the circuit then sequentially wire like labeling although conductors we've got conductor one conductor two conductor three the normally open contact looks like it's labeled with conductors two and three and that is why these are usually labeled two and three on the starter we're going to keep our number two as the return so that guy is there and then sequentially this would be our first conductor - is the return so this is why our number three number four number five and this guy is the same conductor now to simplify things as well that's you know if cleaner diagram but we can go like this as well and then you can see that on either side of that push button it looks like there's going to be two conductors there okay let's use that to now wire up all the components that are on the picture so the first thing we got is we're going to the overload the overload is that's normally closed contact here so we'll pick off line one over to the overload okay this guy is done next thing we need to do is go to the normally closed switch on this diagram are coming in on the left so we're going to come in to the left over on this component as well excellent okay so we've come into the the left-hand side of the stop push button from there it looks like we go to the left-hand side of the start push button again we could just go like this but then we're going to get confused later on when we're doing troubleshooting so try and keep the same convention whatever's coming in on the left hand side is the in on the right hand side is the out of each of the switches from there we're going to go to the quo so we're going to pick up our coil there that takes care of this guy if we're going to throw on our conductor numbers this is one right this is three then from there to the skirts which was four this is conductor number five all right and then from there we just have to pick off line two excellent so that's going to be wire number two right on the only thing we need now is the normally open contact across the the normally open push button so we need to have one side going it looks like this side of that contact goes to this side of that push button so we can go there or we can go right to that side the left-hand side of the club well essentially that is this guy right here so we can connect in the normally open contact to that same point that we're feeding the Kuo the same piece of wire why would you bring another conductor all the way out here the switch when you can just do six or eight inches of conductor and pick up on your a one on the clone again this is usually labeled a one and this guy is labeled a two excellent so we have picked this guy off now we've got to have a conductor going from the left hand side of the push-button over to the other side of the contact so we're going to pick off this guy on the left hand side come over and pick up the other side of a normally open contact this is the three wire control so looking at the conductors in the pipe there are three conductors in the pipe and possibly a bond water depending on which type of condone you use to where to go from this stop start push button station over to the starter all of these components are within the the starter so here we've drawn the fuse disconnect here well not the fuse disconnect but just to disconnect then we've got our three contacts that correspond to this coil these contacts are all horsepower rated this one is rated for less current in that it's just in our controls so it has a lot less current being applied to it currents coming down easy no current is coming down to the overloads right and then going to our three-phase motor okay for taking a look at the components here then these two on a NEMA starter are the coil and again remember I said that those two sides of the normally open contact are often labeled two and three well there they are right there two and three the normally open contact is just tucked in at the back of your NEMA starter okay your main motor contacts are here the current will flow through the heaters at that point the heaters are not placed in there but it would go through the overload heaters and we have line one going to t1 line two going to t2 line three going to t3 and the labels for these guys if they are not there would be a 1 and a 2 for a claw okay so the 2 wire provided us with low voltage release and this guy provides us with low voltage protection in this case if you have loss of power then this coil is going to kick in which will open all three of these contacts which stops current flowing to the motor when power is main is restored to the building current does not automatically flow to this three-phase motor because the current you can see we block by this normally open contact and by this normally open switch here so you have to actually press the push button in order for the coil to be re-energized for these contacts to close and for current to go to the motor so in that case it provides a protection when you have a browner or when you've had loss of power and then you have to press the push button in order for the motor to turn back on

Channel: Pete Vree

Views: 382,216

Rating: 4.8518519 out of 5

Keywords: 3 phase motors, motor control, ladder diagrams

Id: WVJNcNQBIw8

Length: 14min 55sec (895 seconds)

Published: Tue Sep 29 2015