Building a Home Power Monitoring System
	Introduction | Planning | Installation | Software | Wisdom
		Planning Ignoring the development of the software, the main task at hand was to install a current transducer on each branch circuit in my house. The current transducers are actually really small and they clip on to the wiring. If you've never seen nor heard of a current transducer, here is a picture: Basically a current transducer generates a current or voltage (depending on the type) that is proportional to the current passing through the center of the transducer. There is a slight complication however. You can't just clip one of these around a piece of romex wiring since it contains both legs of the circuit. Since the current going out on the hot wire is equal to the current returning on the neutral wire, they will cancel each other out and the transducer will read zero. For the transducer to work you have to clip it around just one of the wires. Luckily, the wires are separated within the breaker panel so clipping the transducers within the panel makes things pretty simple. The second piece of hardware is a board that all the current transducers (CT's) feed into. This particular board comes from a company called Veris: This particular board can handle a 42 pull panel (ie. a circuit panel with 42 individual breakers). My little 100amp panel only has 14 breakers so no problem there. This panel has an RS485 interface and speaks modbus which makes things pretty simple to interface to. However, since RS485 is pretty unusual on PC's I had to add a 485 interface card to one of my servers in the attic: By the way, this is an older photo... the server stuff is now encased in plexiglass and has a computer controlled cooling system that utilizes a series of blowers and an AC unit to keep things cool on those hot summer days... but that's another article. At any rate, this whole project seemed pretty straight forward since my garage wasn't drywalled at the time so I had access to pretty much everything: However, as I started looking into things I realized I was going to run into a few problems: My 100amp electrical panel is a typical unit with integrated meter. This means that the area below for wiring is already cramped. I did a test run and was only able to get about eight CT's into the panel before I ran out of space. The Veris board didn't come with a case or even a cover. It was going to have to be installed in an electcial box itself. This would require mounting the box someplace relatively close to the panel and running conduit to it. I was planning to drywall the garage so this would look pretty ugly. In the end I figured I could install a large subpanel next to the original panel which would give me plenty of space for the CT's and allow me to mount the Veris board inside the panel itself. NEXT >
	Introduction | Planning | Installation | Software | Wisdom

Kondra Systems