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How to monitor the status of your appliances using current sensors


A number of people on the forum recently purchased the Mamac CT-800 switches posted here. I received mine last week and thought I would document my work as I installed them in my Washer, Dryer and Furnace. Please only use this as a guide. I am not an electrician and you should always check with your local regulations regarding making these kinds of modifications to your home. Only follow this guide if you feel comfortable around electricity. 220VAC can definitely hurt you so be careful.

How the CT-800 switches work: In layman's terms, the CT-800's are a current transformer with internal circuitry to open and close a set of contacts, based on how much current is flowing through them. This particular model will have its contacts "open" when less than 1 amp is flowing, and "closed" when 1 amp or greater is flowing. Most devices like your dryer motor, furnace fan motor and washer motor use at least 1 amp while operating which makes the CT-800 perfect for this application.

Without getting too technical, the number of turns of wire through the CT-800's center is proportional to the threshold at which the CT-800 closes its contacts. If you run your wire straight through the center of the CT-800, the contacts will close at 1 amp of current flow. If you put your wire through the hole and then wrap your wire around the outside of the CT-800 and back through the hole so that the wire actually goes through the center twice, then you have cut the current required to close the contacts, in half.

 



A technical datasheet for the CT-800 can be found here.
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Materials Required:

    * Mamac CT-800 Current Sensing Switches
    * Enough single pair (300V or 600V rated) wire to go from the dryer to your automation panel


Take a look at the back of your dryer. Most likely, it will look something like mine with an access hole for the wire connections.


Be sure to unplug the dryer before opening up the access hole. 110VAC doesn't feel all that nice but with dryers you are dealing with 220VAC which can definitely cause some damage.


In the access hole, you should find three wires: a black (hot 1), a red (hot 2), a white (neutral) and a green (ground). To properly monitor your dryer, you will want to look at the hot wire that goes to your drum motor. This way, even when the heater is off and the drum is still turning, you will know. I'm not sure if there is a standard for which hot wire gets connected to the drum motor, but I did a quick test to find out which way mine is wired. Luckily there were nice snap together connectors on each wire so I could easily take each one apart. The above picture shows the red wire apart, ready for the CT-800.


Feed one of the wires through the hole in the CT-800 and connect them back together.


If you are taking on a project such as this one, then you probably have a voltage meter lying around. Using your meter on the continuity or resistance setting will quickly let you know the status of your CT-800 contacts.


Monitoring the red wire, with the dryer to set "Air Only", the contacts are still open.


With the dryer heat on, the contacts close. I've obviously got the wrong wire.


Showing closed contacts with the dryer on "Air Only" and monitoring the black wire.


Connect your wire up to the contacts on the CT-800. Since these are just dry contacts, the polarity of the wires doesn't matter.


Attach the CT-800 inside the back of the dryer some how and run your wiring back to your panel.

In my ElkM1, I set the zone to be "Normally Open" and set up a rule to announce when the dryer shuts off. I am also displaying the status in CQC.
Please only use this as a guide. I am not an electrician and you should always check with your local regulations regarding making these kinds of modifications to your home. Only follow this guide if you feel comfortable around electricity. 220VAC can definitely hurt you so be careful. When wiring inside your furnace, you need to make sure you are using wire that is rated for the heat. My furnace specified on the door that any replacement wiring must be rated to 105 degrees C.

Materials Required:

    * Mamac CT-800 Current Sensing Switche
    * Enough single pair (300V or 600V AND 105 degree C rated) wire to go from the furnace to your automation panel
    * Butt splices, tie wraps, marrettes


The furnace control board and AC wiring is all under the bottom panel in my furnace.


Note the warning message on the inside of the furnace door.


I initially ran the main hot wire coming in to the furnace, through the CT-800 and tried it but that told me when the furnace fan was running. I only wanted to know when the heat is on so that I could have a runtime counter going that would keep track of how much we use the furnace. To accomplish this, I am monitoring the hot wire running up to the exhaust fan. Testing it, I found that the exhaust fan comes on 5 seconds before the gas comes on and then goes off when the flame goes out.


Furnace just kicked on and contacts are "Closed".


Furnace flame has shut off and fan is running. Contacts are "Open".


While I was working on the furnace, I decided to run three more belden pairs so that I could control it from the Elk. From my touch screen, I can turn the heat on, the fan on, or switch the control back to the regular thermostat on the wall.

 


Please only use this as a guide. I am not an electrician and you should always check with your local regulations regarding making these kinds of modifications to your home. Only follow this guide if you feel comfortable around electricity.

Unfortunately there is no access hole on the back of my washer so I could not easily get at the wiring inside without taking the whole back off. Instead of going to all of that trouble, I decided to build a quick universal box that I can plug any 110VAC appliance into.
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Materials Required:

    * Mamac CT-800 Current Sensing Switches
    * Enough single pair (300V or 600V rated) wire to go from the appliance to your automation panel
    * One computer power supply cable and one female plug end
    * Single gang box
    * Marrettes, strain reliefs


Cut the computer power supply end off and wire the female connector on. Cut the cable in half.


Pop out the hole on each end of the box and screw in your strain reliefs.


Run one end of the power cable through each strain relief into the box.


Attach the green (ground) wires to the ground screw in the back of the box.


Run the black (hot) wire through the CT-800 and twist the two black wires together. Twist the white (neutral) wires together without running them through the CT-800.


Throw some marrettes on the wires to keep them together.


Drill a hole in the side of the box and run your belden status pair in. Connect it up to the contacts on the CT-800


Lay the CT-800 down inside the box. Everything fits quite nicely.


Connect up your washer or other appliance and run the belden pair back to a zone on your panel. I need to go buy a cover for the box.

I haven't come up with a way to put in a delay in the Elk on the washer status. As you know, the washer stops briefly between cycles. If you have the Elk announce each time the contacts close, then you will have 5 or 6 announcements each time you put your washing on. I only just received my elk last week and haven't got too deep into the programming. If I was programming a PLC, I would throw a 1 minute timer on the input and use the "Timer Done" bit to trigger the event. That way, if the washer stops for less than a minute (in between cycles), the timer will not expire and I won't get my announcement. I'm sure there must be a way to do this in the elk.

Edit: To write this in the Elk, you could go:

WHENEVER Washer Status (Zn 2) BECOMES SECURE
       THEN TURN Output 100 ON FOR 1 MIN, RESTART TIMER IF RUNNING
WHENEVER Output 100 STATE IS TURNED OFF
       THEN ANNOUNCE Miscellaneous 3 (vm241)

 

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