How to Check a 240-Volt Outlet for Voltage

Fred's Appliance Academy
February 28, 2020
Dryer Training

Hey, everyone. Tim with Fred’s Appliance Academy here with another great video for you today. In today’s video, I’m going to show you how to properly check voltage at a 240 volt, three and four-prong outlet. It’s very important that we check the voltage. This is the most overlooked diagnosis in a home. I know I’ve said that before when we checked our 120-volt outlets. We’re going to use this dryer here as an example and I’m going to show you how to check the voltage here by using this clear plastic sleeve with a white piece of paper inside of it and a dry erase marker.

We find drawing the outlets out really help to diagnose that outlet. What we’re going to really need to do first is we’re going to have to disconnect the voltage supply from the dryer for safety purposes first. Once we have the power disconnected, we’re going to have to remove the terminal block cover here with this quarter-inch screw and we’re going to want to go ahead and place this cover and the screw off to the side so we don’t lose that screw. We can look at the cord here, the cord has been properly installed. We have a strain relief and we have our line voltages and our neutral in the correct spot with our green ground strap here indicating that the unit is grounded.

Now that we have this exposed, we’re going to go ahead and reapply power to the unit and we’re going to use our volt ohm meter here to check the voltage. Now I’m going to prop this up so we can see exactly the voltage we’re getting at each leg. I’m going to set this for volt AC. The first thing I’m going to do is check the two outer legs and I should have 240 volts there. I’m showing 230 volts, which is showing a good voltage rating. With this, I’m going to go ahead and draw this out on my clear plastic sleeve indicating I have 230 volts.

The next step is you’ll want to just stay right here across the two legs. Just bring one lead of the meter right into your neutral and we should see approximately 120 volts and that’s also going to be plus or minus 10%. We’re reading 114 volts. I’m going to go ahead and mark that on my paper. With the readings I received, it’s really not necessary to have to go and check from neutral to the other leg because the two outer legs showed that we already had 240 volts. But if you want to do it just for purposes of being thorough, that is not bad to do as a good technician. We could show that we also have another 114 volts.

When looking at our paper and when we have it drawn out, I can tell that we have a good outlet. I have the voltage range between the two legs and then the voltage between the two 120 volt and neutral legs. That is diagnosing a good outlet.

We’re now going to show you how to check a 240-volt four-prong outlet. Now, this is going to be a four-wire cord, so we’re going to actually have a ground and a neutral. I’ve already got the back cover taken off here. I’ve got my drawing drawn out, so all we really need to do is check between our two hots and make sure we have a ground and a neutral there.

The first thing I’m going to do is I’m going to go ahead and I’m going to check between my L one and my L two and I should have about 240 volts plus or minus that 10%. We’re showing about 232. So on my drawing I’m going to draw between L one L two; 232 volts. I’m now going to go ahead and this is where a lot of technicians get confused because they check the outlets and then they move their meter leads around and they forget what they checked. So what I always suggest to do is start from L one L two and bring in one of the meter leads to check for neutral and then check for ground.

Both are showing that I have 116 volts so I’ll make that on my drawing. Between the L one 116 volts and the L one to ground, 116 volts. In this state that we’re at right now, do we really need to go any further? You ask yourself that? No, but if you want to be that thorough technician, go ahead. Check between now your other leg to neutral to ground. I’m showing that we have a 116 volts and I’ll make those drawings on my sheet of paper here. When we have our drawings and we’re looking at our sheet of paper here, it’s showing that we actually have the proper voltages. By drawing it out, it really gives you the picture of if there’s anything missing.

If we had anything missing on any of these voltages there, yes there would be a call for an electrician, but it’ll also help you explain to the customer of what’s going on in the outlet. If you just tell them, “Hey, you need an electrician,” they call an electrician, they charge a service call to come out and they find there’s nothing wrong on the outlet, it’s something that’s in the appliance itself. So drawing it out, being able to show the customer to be accurate on these diagnoses is going to take you a long way. And again, it’s an overlooked diagnosis when it comes an electric and appliance.

I really hope you guys found this very helpful. Hope you like the video. Hope you actually like everything that we’re putting out there for you. We’re trying to make your jobs and lives a lot easier when you’re on the road. I’m Tim from Fred’s Appliance Academy, where we’re training tomorrow’s technicians today.


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