All right, so this quick video here is about three phase voltage imbalance and I just want to talk quickly about why it matters, and so, when you see these, this is actually an article that I did a while back at HVAC, our school comma tech tip and Just talking about voltage imbalance, and so when you think of three-phase, is you have three different phases of power that are out of phase with each other, but they're not they're, not the full 180 degrees out of phase with each other like we're like we're used to, And so because of that, we have about 120 degrees phase difference between each of you take 360 divided by 3, that's 120 degrees of difference from peak to peak in between the three phases, and so it's really important for a three-phase motor for it to work properly And not to overheat, not to have long term issues for the voltages to be the same on the three phases. Generally speaking, when we have issues with imbalance between the phases, it's generally due to a voltage drop on one of the phases, and that can be due to an issue where it's connected into a breaker down the line somewhere. A disconnect could be a lot of different things can cause it, but one of the more common causes would be the actual controls inside the unit itself. So the contactor or starter - that's feeding a particular device.

So you can have three phase voltage imbalance coming into a unit say a packaged unit or something or you can also have three phase voltage imbalance coming out of a contact for a starter or something so that the t1 t2 t3 lines. And so, when you calculate voltage imbalance, what you're actually doing is you're taking all three of them and measuring them all together, so you're doing every combination and then you're coming up with the average and then you're seeing the percentage of difference based on the average. That's that's essentially how the math works out from a practical standpoint, though, what am I gon na do in the field when I want to measure three-phase vultures imbalance, I'm gon na know if you can see my cursor here, so I'm gon na point here. So I take my contactor and I would measure between each leg and l1, l2 and l3.

This is generally going to be really only effectively done if the system is under load. So if it's actually running so I'm gon na measure in between each of the three and then I'm going to figure out what the average is of the three. So you take the three multiply them times each other and they're divided by three and then that's going to give me what my average is and I'm gon na compare what I have on each leg to my average to come up with the percentage of difference. Again.

That's a lot of math, but you know from a typical method that you're gon na do in the field. You're, really just looking at it to see. If you have anything that seems out of balance you're, not necessarily on every single service call gon na, do a voltage drop calculation, because they're generally gon na be very close to each other, and it's not generally gon na be a concern. But in some cases you may be tasked with doing a voltage drop calculation and that's how you do it.

And so you would do it under load on the L side. And then you do it under load on the T side. And if you saw a significant difference, then that would indicate that it's, the contactor starter, that's causing the problem. But another thing you can do - and I just talked about this on the most recent podcast talking about using your volt meter as a voltage drop device.

If you want to just test your control, you can put one leg of your meter here: one leg of your meter here so l1 to t1 and measure and see if you have any voltage drop and then do the same on the other two now the question Comes up, what is an acceptable voltage drop across a contactor relay really depends on the voltage. I don't have an exact number for you and I know I know you probably wish I did. But, generally speaking, if you see anything approaching a volt, that's usually starting to become a problem, and now you can compare to other relays and contactors on equipment nearby and that'll. Give you a really good baseline in general, it's good to compare to other similar devices and see what you're getting but that'll give you some sort of indication of where you stand by measuring for voltage drop across so you're, actually taking your voltmeter.

Putting one leave there. One lead there, but then you can also do your your three-phase balance calculations. So if you go down further into this article, we talked a little bit more about what is acceptable and unacceptable, and I just want to cover this really. What we look for is, we would love to see voltage imbalance of no more than 1 %.

That's what the Department of Energy talks about from the standpoint of optimum efficiency, we'd like to see less than 1 % variation up to 4 % is acceptable based on some industry sources, but I would like to see anything above 1 %. You start to look into it and see what you can do to reduce it. So that's very, very little change. Let's say you had 240 volts three or forty volts between phases, then that would only be 2.4 volt difference from the average.

As soon as I started. Seeing anything more than that, I would want to start looking into it, but just to make it even easier. We created this voltage imbalance, calculator that you see here, there's a link for it at the bottom of this video. If you go to the resources tab, you hover over the resources tab and then you scroll down to where it says, voltage imbalance, calculator.

This is also available on a mobile version, but it requires that you, like click, a little tiny arrow, I'm gon na work on making that a little easier. Then it'll pull this out open and you can see it's HVAC school.com force less resources for its last voltage. Your balance, calculator, which is a tricky because you got some dashes in there too, so I should make an easier link um, so just to give credit where credit's due I worked with my web developer to help make this voltage a calculator and the original version of This was a spreadsheet made by Chris Kimmel Eddie. So thank you Chris for making this.

So if you just measure your different l1, l2, l1 l3 whatever - and you can also do this on the T side - like I mentioned it - doesn't have to be on just the L side. So let's say we had 240 volts and then we had 237 on the other one and then on the other side we had 242 once you get them all entered. You calculate voltage imbalance and it's going to tell you whether or not you are in the acceptable range. Our voltage imbalance here is 1.1 1, which is going to result in a 2.4 8 % motor temperature increase, which is kind of a cool little thing we added in there.

What this is saying is it's advisable to decrease in balance to below 1 %, if possible. So, let's look and see if there's any way, we can reduce this imbalance, but let's make it a little more extreme and we'll increase that range a little bit now. We've got a over 4 percent because now we're between 249 and 240, our average voltage is two thirty nine point. Six seven and now our motor temperature increase is a whopping.

Thirty, two point: five four percent. So that shows you why it's so important to keep your voltage properly imbalance, so hopefully that's helpful. You can always find out more by going to HVAC our school comm. That is the website, and that's where we have a couple handy calculators.

Thanks for watching we'll talk again soon.