[How-To] Appliance monitor


How to monitor an appliance on/off status via an X-10 signal.

Here is a way to monitor your appliances to tell if they are on or off via an X-10 housecode signal. Uses include washer/dryer monitor to tell when they turned off.

Items needed:

The sensor is a CR Magnetics current transformer part number "Model 19" which can be found here


The Power Flash module is made by X-10 and is available here


Heavy duty extension cord (capable of supplying 20 amp loads) or material to make your own extension cord using male and female 120 VAC adapters and 12 awg wire.

Short piece of 12 awg wire.


This current sensor is made to monitor AC Current and light an LED if the current exceeds two amps. It senses the current going through the appliance's hot wire which is run through its center hole (note to leave the insulation on the wire as the current will still be sensed).

Instead of using this sensor's output to light an LED, you can instead hook the wire outputs of the sensor directly to an X-10 Power Flash unit (with input set to "A" and mode set to "3").


First modify a heavy duty extension cord so the "hot" wire is exposed. If you don't want to use an extension cord, then make your own short extension cord using male and female plug receptacles and 12 AWG wire. Be sure to wire the hot, neutral, and ground wires in the correct order.

You will then run a short 12 awg wire thru this current sensor and connected it in series with the exposed hot wire from the extension cord (see photo below). You could use wire nuts or splices to attach the wire. Be sure cover any exposed wires with electrical tape.

For this test I then connected the extension cord and power flash into 120V AC outlets and attached a heat gun to the female end of the heavy duty extension cord (to act as a test appliance).

I monitored an X-10 log via Homeseer. Whenever I powered the heat gun on the power flash would send out its house code plus ON. Whenever the heat gun was turned off the power flash would send out its house code plus OFF. Note that the heat gun drew seven amps so it was well above the threshold of this sensor's two amp trip point.

If you needed a lower trip point you could "loop" the wire through the sensor (so it passes through the center two times). This would lower the trip point to one amp.


I initially wanted this sensor to trip a relay to give contact closures so a "game port" or my SECU16I/Ocelot could detect it, but haven't had time to test this yet. The voltage supplied by the sensor is AC though and small and I doubt it has much current drive capabillity so selection of a "high resistance, low voltage" relay coil is essential.

One other nice thing about the heavy duty extension cord modification shown is that it makes current measurement via a multimeter really easy (of course tape the open wires during operation to avoid shock and shorts). This measurement would be needed if you were not sure that the appliance you wanted to monitor drew over the two amp trip point.


Here is a little update on monitoring currents for a washer and dryer.

I have a mid-size Maytag washer and gas dryer and I measured some currents while they were running. Both units are 120 VAC powered.

I used a Fluke Multimeter and a "split" hot wire connection from a heavy duty extension cord. (See photo for setup).

The dryer pulled a little over three amps while in the drying mode (well more than the trippoint for the current sensor).

The washer on the other hand would pull only 0.1 amps while filling with water (because only a solenoid valve is on during this time), but would then pull around six amps during the other cycles.

So if this method of current monitoring would be used for monitoring this washer, a timer or sequence script would have to be incorporated, since the trip point of the current sensor is two amps (plus you would have to do to many multiple wraps with the hot lead to get down to this trip point).

Because of this problem I posted another "How-To" for monitoring the washer cycle.


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I saw those other posts over at HS forums. I'm wondering now if maybe that other current transformer might have more current drive than the one I am using (easier to trip a relay). Might have to look into getting one of those also.
The other huge advantage in some cases is the split core that can snap around existing wires.

One more thing to point out about these current transformers. If you want a more sensitive setup just wrap the wire around the current transformer more times. Each time you wrap the wire around it doubles the sensitivity. We do that here at work using HAL effect current sensors.


Well my old dryer died and so did my dryer AT&T TTS voice alert message. Not to let the wife down I soon came up with another solution. One that involved not voiding the warrenty for the dryer.

I ordered a current transformer (http://www.crmagnetics.com/pdf/3110.pdf) and a Poweflash unit. I hooked up the CR-3110 across the Powerflash terminals using a 1000 ohm burdon resistor across the input contacts. I set the Poweflash to Mode 3 and Input A.

I needed to monitor the dryers AC current without cutting into its power cord and after some thought I finally came up with a quick solution. I picked up one of those super short heavy duty extention cords from ACO and using a sharp knife carefully cut back some of the rubber exposing the insulated wires (make sure you don't cut through the insulation on each wire!!). I wrapped the black wire around the CR-3110 (trial and error until I read 5-6 volts AC when the dryer was running) to trigger the Poweflash unit.

It works great. I setup my event to trigger when it receives the X10 off command for the Unit code I chose. The wife is happy.

Along the line of what John W was saying about multiple wraps, there are ways to "fine tune", the wraps....

I'm using some completely made-up numbers here for this example. But this could be similar to some low-power device, like a DVD player or cable box.

The problem with using current sensors to monitor the on/off status of a device is that some devices have a very subtle difference between their standby power and their powered-up power draw.

Let's say you have a current sensor that trips at 1 amp. You have a device you want to monitor that uses 0.5 amp in standby and 0.75 amp when powered-up. So you'd have to wrap the "hot" wire around the current sensor twice in order to get it to trip when powered-up... the problem with this is that it will also trip when in standby, because two wraps x 0.5 amp = 1 amp, which trips the sensor! Using the old analogy that current through wire is like water through a pipe, you have to divert some of the water in order to have a fraction of the water (current) go through the current sensor.

In the case of the above example, you would split the "hot" wire into two leads. One lead would bypass the current sensor. You now have each lead carrying 0.25 amp in standby and 0.375 amp when on. Three wraps of one of the leads around the current sensor results in 0.75 amp in standby and 1.125 amps when on. This is perfect for tripping the current sensor ONLY when the device is on and NOT when it is in standby. You can get even smaller increments by using more leads (like three leads, with two bypassing and only one going through).

Glad you got your setup working!!

One of the advantages to using the current transformer I used was it has a two amp "threshold" trip. In other words, it will develop the same voltage across its leads as long as the current it is measuring through its core is over two amps.

I selected two amps because I knew my dryer draws well over that in its "heat" cycles. Also, this device will drive an X-10 power flash directly (I didn't need any other external resistor).

Of course the disadvantage is it is not a split core. ;) How much did that split core run?

Thanks for the input!

whatever the good solution is, let Martin know so he can carry the hardware ;) I need to monitor a washer, dryer and water softener ...

I am interested in how you finally got your measurement working for your Water Softener. Most softeners are run by low voltage (12V or 24V) transformers that run a timer or electronic servo system. How did you do it?

I would like to measure when my Water softener is recycling, and also, when my furnace blower motor is engaged. Any suggestions? I like the idea of the split core sensor, so i don't have to mess with the OEM wiring setup.

Any ideas?

Hi Jim, one option for monitoring the furnace is a simple "flap" that is mounted inside a airduct. By mounting a DS10a magnetic connector on the flap, you can sense when it is moved by air. I suspect that you could even rig one on a floor register is the air flow was sufficient.
HERE is how I wound up measuring the salt level in my water softener.

It has some hiccups, but there is a mod coming out by Gerry for better "request to send" signals for that unit. ;)