Goldline/Aquarite Chlorinator electrical problem--what went wrong?
You've already sorted this out, but the lesson here is simple: Don't ever assume anything. 

Determining 220 vs 110 at the panel is fairly simple. You have a phase A and B in your house, which come from each side of the transformer. The transformer is center-tapped to ground, and this is your neutral wire. 

"Voltage" is really just a measurement of potential difference between two points, and so if you think of it that way, the voltage between A and B is 220V, and the difference between A and neutral or B and neutral is 110V. 

In your breaker panel, every other row of breakers is a different phase. 



To get 110V power, you need a neutral wire, and a hot wire from either phase A or B (it doesn't matter which). So any single breaker, like #3, is only supplying 110V power. 

To get 220V, you need one hot on phase A, and one on phase B, like the 220V breaker at the bottom right (#4/#5). 

This picture also includes some tandem breakers (the one currently being installed is a tandem), in which case both circuits are on the same phase. That is, both #1 and #2 are on phase A. If you measure the voltage (potential difference) between #1 and #2, you'll get 0V.

Voltage between #1 and #4 is 0V, and between #3 and #5 is also 0V. 

Voltage between #3 and #4 is 220V, since they're on different phases.

Note though, it's against code to use single circuit breakers to run a 220V circuit, since if the power trips, you want all the power to trip, not just one side (since that would leave 110V hot).



The other huge tip-off at the circuit is the wire colors (though again, never assume, always test). There aren't a ton of requirements for wire colors, other than two: white means neutral, green (or bare) means ground. If you use a white wire for something other than neutral (common in a light switch, for example), it must be indicated on both sides, usually by wrapping a piece of red or black tape around it. Black is hot. 

The next most common color is red, which has two very typical meanings: 
 * switched, which you'll commonly see in duplex receptacles where one is constant, and one is controlled by a switch
 * hot for 220V, which is the case here, where red is the opposite phase from black, to provide 220V.



To sum up:


In the panel, a double-sized breaker on the circuit means 220V 
At the branch, not having a white neutral wire means you can't get 110V.