 In this video, we're going to be discussing paralleling single winding transformers. Now remember, when it comes to paralleling transformers, there's three rules that have to be obeyed. Number one, you have to have the same voltage ratings of the transformer, and that has been covered in another video. Secondly, you have to observe the instantaneous polarity. Now that is not to say that they both have to be subtractive or both have to be additive, but that's what we'll discuss in this video. And thirdly, they have to have the same percent impedance. So let's get ahead and go ahead and start talking about how we are going to parallel a subtractive polarity transformer with an additive polarity transformer. It seems like it can't be done. Oh, but it can. Now when we go ahead and we are paralleling the transformers, the first thing we do is we basically stop time and we pick a polarity. So what we're going to do is we pick the line polarity here. I picked the top as being negative, the bottom as being positive. That doesn't matter. You can go ahead if you want and pick the top as positive, bottom as negative. It seriously doesn't matter. It's all going to follow through all the way down to the secondary bus. So right now for this example again, negative on the top, positive on the bottom. Now when you pick the line polarity, the line polarity ends up determining the primary winding's polarity. So we see here that we have a negative line. Here it goes down. That's going to make H2 negative and H1 positive because that's hooked up to the positive line. Same thing down here for the second one. I've got H1 as positive. H2 is negative because the H2 is hectic to the negative line. H1 is hooked to the positive line. So again, you pick the line polarity. The line polarity determines your primary polarity and then your primary polarity determines what your secondary polarity is. So here we go. Remember that with the rule of transformers, H1 and X1 are always going to be the same polarity. So here we've got H1 is positive. So X1 is going to be positive, which means that if H2 is positive, X2 is negative. Over here, I've got H1 is positive, which means that X1 over here is positive. So watch out for that because over here it was across the way. Over here, X1 is positive, H2 is negative, X2 is negative. So again, you pick the line polarity. The line polarity determines the primary polarity and the primary polarity determines the secondary polarity. And then from there, that determines what your secondary bus is. So I'm just going to go ahead and I'm going to use this transform as my reference. Now you see here I've got X1 is positive and it is connected to this line here. That makes this line positive. This is X2 is negative. It's connected down here. That makes this negative. So what I have to do now is make sure that this transformers windings are connected the same way. You want the negative lines to be touching and you want the positive lines to be touching. Or else you get cablazzoflam. So we have here negative X2 is down here. It is on the negative line. We're all good. And X1 is on the positive, which is here, which is connected to the positive line and we're all good. That folds through as long as you've got your polarities matched up. It doesn't matter if these windings are all swapped out. As long as by the time you get down here you've got a positive line, which all the terminals that are positive are connected to, and a negative line, which all the negative lines are connected to, you are good to go.