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.
* 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.
Edited by Squiddy, 26 October 2008 - 11:16 PM.