# Question about monitoring clothes dryer

The circled breaker is a 30A for my clothes dryer. I think this is 240 and could be monitored with a single 50A CT. I’m assuming that the only way to make absolutely sure is to trace the wires back up and make sure there is not a neutral?

Just look at the dryer plug. If it has four blades, it has a neutral.
EDIT This is wrong, both the three prong and four prong have a neutral and are 120V/240V.

Another way is to put a ct on each conductor and run the dryer for a minute. If the two are different, there is a neutral.

But it may be fine to treat it as a 240 only appliance, depending on what you are trying to accomplish. If you want to identify every Watt consumed in your house, you need to capture the 120V component. If you are trying to arrive at a short-list of major consumers and subtract that from the whole to get an “everything-else” number, maybe you can treat the dryer as a 240V appliance.

Here’s a cycle of my dryer:

You can see that the whole thing sits on a base of about 200 Watts. That’s the 120V motor. I zoomed in on the motor during the cooldown cycle and got this:

Average 203W. So the whole drying cycle took about 51 minutes. Call it an hour. Total energy was 2.43 kWh. The motor ran the whole time at about 200 Watts. That’s 200 Wh. The 120V component is about 8% of the total.

So if I were to measure just one conductor, the result would be 8% high or 8% low depending on whether that conductor carries the 120 component. You can determine this by running for a minute with a CT on each. Assuming you measure the -8%, in this example you would see the dryer using 2.23 kWh and 0.2 kWh attributed to your “miscellaneous” category.

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Just checked, looks like I have 3 blades (+ ground) - so I think I have 240 and can monitor with a single 50A CT?

Thanks!!

I consider the ground to be a blade. That connector has a neutral. The dryer can use 120V.

Edit: just looking at the three prong plugs and they appear to be 120V/240V as well, no ground.

here’s what I see with a single 100A CT on with it running:

Hmm, my dryer is about 5kW. Did you check “double” on that? The power factor is .99, which suggests to me that you have the leg with the 120V motor. If you run the dryer on tumble only (no heat) you should see the motor only.

If your dryer is anything like mine, and they are all pretty much alike, the motor draws about 200, so the other leg should be about 2400 Watts, for a total of about 5kW. If all that bears out, id recommend monitoring the other leg if you are going to do just one, and leave the motor to miscellaneous.

It was on the 120 leg. I moved it over to the 240 and it shows ~2400 - so I should just make sure “double” is checked?

Yes. As explained above, the Watts will not reflect the roughly 200W of the motor. To get the total you would need to run the other lead through in the opposite direction or use two CTs.