Living in Northern Ontario means frequently using a block heater to start your car on a -35C morning. For those of you lucky enough to live in a climate where you've never heard of a block heater, here's the wikipedia entry: http://en.wikipedia.org/wiki/Block_heater

One of the fears of winter driving is getting in your car at 7:00 in the morning, turning the ignition and all you hear is "Errrrr...errrrr...click...click...click" then nothing. Maybe it was the wind or a stray dog that unplugged your cord or it could even be a bad cord or heater, either way you're calling a cab to get to work. There are quite a few manufacturers that include a little status light in the female end of an extension cord but as far as I'm concerned this is next to useless because it is just an indication of available power not a test of the actual load. What I wanted was some way to sense the current draw, kind of like a clamp-on ammeter.

After a bit of internet window shopping, I came across a device that did almost everything I wanted. For about $20 you get a little adapter that you either plug in between your cord and outlet or cord and block heater and an LED indicates current. Perfect...except that I sure don't want to venture out in the deep freeze, to check that little light, any more than I have to.

This then is my project: A current monitor that can be embedded in an outlet box inside your home so you can monitor the use of a block heater or roof heating cables etc.

Step 1: Warnings

Before you go any further here are a few caveats that you need to be aware of:

1. Although the final circuit is electrically isolated from household 120 volts, a line voltage lead needs to be disconnected from the switch, passed through the coil and reconnected.
2. You need to comply with any electrical or building codes in your area.
3. I am not responsible for any misadventure, this instructable is just to show you how I did it.

Before starting on my project I sent in a question to Ontario's ESA (Electrical Safety Authority).
Here was my question and their response:

"I am considering installing a current transformer in the interior switch outlet for my exterior outlet feeding my car's block heater. The transformer supplies 10mA to an LED installed in the switch plate. The transformer is a toroid that the switched load simply passes through so there is line voltage isolation. Are there any concerns with this?"

"To get a technical advice about your project, ESA highly recommends contacting a licensed electrical contractor. You may want to check the following link for a list of Licensed electrical contractors in your area: http://www.esasafe.com/GeneralPublic/hc_003.php?s=8"

After asking a few local contractors it was clear that they had no idea of what I was talking about.
Oh well, I tried. On with the project.
<p>I am looking to take this concept slightly further and wanted your thoughts..... I would like to install a device that will monitor the amount of current used while the light is on. You can purchase the &quot;Kill-a-Watt&quot; device that will do this for anything that device that plugs in but i can't seem to find a way to accurately measure the amount of current used in single light fixture in my house. You can take a guess as to how long but having something that would essentially do what the Kill-a-Watt device does would be very beneficial. I also live Canada and am always looking for ways to track exactly how may hours each light is on in each room. The 2 Gang faceplate you are using in this picture is what made me want to contact you. The one side appears to have a small LCD panel on it. I was thinking if you could make such a device it could be installed similar to your 1st image with a LCD readout indicating what the fixture has drawn for current. If you have any ideas or know of anything online i would certainly be interested.... (PS- I am just finishing my 1st year electrical apprenticeship as well which is where the recent obsession with conservation is coming from :)</p>
<p>rmhome, there are some nice units that display a digital readout for the current as well for around $10. Do an Ebay search for &quot;current transformer voltmeter&quot;. If I understand you correctly though you also want to log the power usage as well. If this is the case and you're a DIY type, I suggested investigating embedded micro-controllers such as the Arduino. The Arduino has tons of home automation projects and the learning curve is real easy. You can pick up an Arduino or Arduino clone for between $10 -$20. The Arduino has lots of 3rd party plugin sensor and output modules called &quot;shields&quot; that do everything from motion sensors to temperature probes. Just google &quot;home automation arduino&quot; and you'll get over a million hits. Hope this helps.</p>
Thanks for the comments. For some reason the Recaptcha spam filter won't let me post replies. <br>For RushFan (Rush as in &quot;Tom Sawyer&quot;?): LOL It must seem funny when Canadian tourists drive to Florida, half of them with block heater plugs hanging out of their front grills. Probably looks like all we drive are electric cars! ;-) <br>For Lectric Wizard: I probably should've titled my project &quot;Heating cable current monitor&quot;. The more I think about it, the more possible uses I come up with. Anything like lighting that's clearly evident when it's on and working is not relevant but possibly some remote loads like a security light or an exhaust fan in your attic. <br>
This is a great idea. I live in a Manufactured home in Canada. One of these is going on my heater cable for the water pipes before next winter !! THANKS!
Excellent! I live in Florida, so I have to admit I had no idea WTH a block heater was, but now I do, and if I even need one, I am going to use your instructible!

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