Is it possible (or advisable) to build an Arduino device so that I can connect a CT to every circuit on a home electric panel? There are about 25 circuits. (This is in the US, if that makes a difference.)
I will have a tenant whom I'd like to bill for their energy use and they occupy half of our house and approx half of the circuits, but all of the power is on one central panel.
Any advice would be appreciated.
Re: Connecting every breaker on a panel?
Yes it would be possible. But advisable or practical - that's another question. Seriously, get an electrician to tell you how practical it would be to segregate the tenant's circuits onto a separate panel, fed by two of your circuits via a second meter, and of course the cost involved.
Then weigh that up against what you have to build: if you want 'continuous' monitoring, and you really do for revenue purposes, you need a processor with several ADCs (the Atmel ATMega 328 that we use only has one multiplexed across 6 inputs and that's hard pressed to measure 4 currents and one voltage), you need two voltage inputs and 25 current inputs, each with a CT. Even if you don't need 'continuous' monitoring and you're prepared to charge based on a sample power measurement every 10s say, you still need the same number of current inputs but you can switch between them with a multiplexer. There may be a small cost saving but offset by an increase in circuit complexity.
People have built systems with getting on for that many inputs, but not for that reason. What they are normally interested in is individual appliance consumption.
Re: Connecting every breaker on a panel?
Adding to what Robert said above, it is possible to use the measurements if you want to jump the technological hurdles.
We have installed an EmonTx for the purpose of "approximate bill sharing" at a residence with a separate granny flat. Fortunately in this case there was a single breaker in the main panel that fed the granny flat's sub-panel. We were able to measure the power using 4 CT's (2 for main, 2 for subpanel).
Here is the dashboard showing real time use and history:
http://data.peakmonitor.com/proto5
25 circuits: I have had success using multiple EmonTX's, and also combining several circuits into one CT (provided that they are on the same phase, and that there is enough slack in the wires in the panel to manipulate them (rare in a modern US tract home panel, but common in older or commercial panels)). Using this method you might be able to get the number of CT's down to a reasonable number, perhaps 8 or 12.