For those of you who have always assumed that in order to control a tank system with probes you have to have something like a B&W probe system to monitor the water levels, I have news for you. I recently refurbed the control on a booster station and well site where there were two probe systems on two tanks. The probe system controller was bad so since this was an emergency call out, I decided to try something I had been wondering about. It turns out that the Snap-IAC5 module is custom made for sensing water levels in a tank via standard probes. Since the impedence of the IAC5 is 169k ohms the current level at each IO point at 120vac is 0.71 mA. In practice it turns out that it actually runs about 0.66 mA and works very reliably. Be sure to connect the 120 vac on the high side of the module and the tank probe on the low side with the neutral connected to ground. If you're concerned about liability, then you can use a 125mA GMA fuse in series with each IO point or you could go the extra mile and use an isolation transformer with a resistor to limit current flow to less than 5 mA (it takes 10mA to be lethal).
The station mentioned above has been on line for several weeks now and is working flawlessly.