 This is going to be a walkthrough of how you do the AC voltage closure test. What that is, is when you are paralleling transformers, you have your primary side there, your secondary side there for that transformer, and your primary side there and your secondary side there for that transformer. You need to make sure that you have everything connected properly before you go ahead and make that final connection. So that final connection will be from there to there. So what we do is use a voltmeter to check the voltage. We would expect to read somewhere close to zero from there to there. If you read anything more than that, which would be double, probably close to 480 volts in this case, you would experience what I like to call a kublasel flam. So what we're going to do is we're going to do a quick walkthrough of how we determine what that is. First things first, as always, with every single transformer, let's get our voltage ratings in. Let's start out with that. Now we have the voltages down. We have 600 and 240 volt transformers, sorry. So we take the voltage, it's pretty easy for this one being the single windings on top and bottom, so it's 600 volts, 240 there. And again, just like every transformer we ever deal with, you take the lower voltage and that is the voltage rating of the windings, the lower voltage, the voltage rating of the windings. The next step is we need to determine polarities. This is very, very important, instantaneous polarity. What we need to remember is that our line here will determine the polarity of the primaries and our polarity of the primaries will determine the polarities of the secondary because remember that H1 and X1 will always have the same polarity. H1 and X1 will have the same polarity there as well. Let's put some polarities, we'll put a polarity on the line. So therefore I have determined that this line here is going to be negative, this line is positive, you can swap those around, it doesn't matter. This is as long as you follow your instantaneous polarity the whole way through. That means that now H1 on this side is going to be positive, H2 will be negative, on this side H1 will be negative and H4 will be positive. So now we've taken this line here and provided the polarities for my primaries. Now I'm going to take the primary and determine the secondary's polarities from those. So now we have determined what the secondary polarities are. H1 was positive, X1 is positive, H1 was negative, X1 was negative. And now we can go for a little what we like to say the current car drive to figure out what that voltmeter is going to read. What we're going to do is we're going to drive starting on this end of the voltmeter, we're going to drive across this winding staying on the road, then drive across that winding staying on the road until we get to here and we're going to see what our potential difference is. If we read zero volts we're good to connect. If we read twice the voltage, in this case it would be 480 volts, we do not connect because we will experience cablazol flam, which means we're letting all the smoke out of the wires. So let's take a look here. What are we going to get? Positive to negative 240 because those guys are in series, negative to positive 240. So I'm going positive to negative 240, negative to positive 240. Those two guys cancel each other out and I have zero volts, which is good, which means we can safely connect from that point to that point there. However, let's see what happens if we have these polarities messed up. So I've got HX1 over here, X4 over there. Let's make this more of an additive style transformer. So I'm going to move X4 over to here and X1 over to here. Let's see what happens. So now I have swapped X4, X1, X3, X2. You know that if H1 is negative, then X1 must be negative. So let's get that in there and bring this guy and make that negative, which will in turn turn that into a positive. Let's take a drive in our current car and see what our voltmeter is going to read when we hop in there. If I go negative to positive 240 and then another negative to positive 240, I'm going to get 480 volts and therefore it would not be safe to connect there to there. And that's it. That's how you do your closure test. You get your ratings in here. You make sure that all your voltages are going to line up. You take your primary side and you assign an instantaneous polarity. Your primary side determines your primary windings polarity there and there. Your primary winding polarity determines your secondary polarities there and there. Then you take a drive and you go across the windings and you stay on the road from one side of the voltmeter to the other and you would expect to get close to zero volts. In real life, you'd probably pick up a little more voltage than just zero. If you read double the voltage, do not make that connection. You have the wrong polarities. And that's a walkthrough of an AC voltage closure test.