These transformers are 120VAC input with 2kVAC output. Just wire the cores together (the cores are normally one of the HV terminals) and wire the primaries so they oppose eachother. If you don't get a nice arc from this switch the input leads on one transformer. This will not arc over that far, but if you start a small arc you can pull it out to about 5". These transformers will make an excellent supply for a Jacob's ladder. You will need at least a 20A breaker to run two of these. Watch the ouput of these they are 1000VA a piece. At 500mA at 2kVrms the ouput could easily kill you in an instant. There are several variations of these transformers. I also have a 4kVrms unit that was taken from an old "radar range" microwave oven. Normally these transformers will also have two leads that come out of them. These leads can be clipped off since they are just low voltage windings that power the filament in the magnetron. Also it is a good idea to use power-factor correction capacitors on these. Use an AC capacitor to do this with a rating of about 30uF.

Adding the capacitor will keep your 15A circuit breaker from tripping. The reason the breaker will trip is because the current is not in phase with the voltage. The current lags the voltage in inductive circuits and current leads the voltage capacitive circuits. Combining the inductor (transformer) and the capacitor will make the circuit seem more resistive to the source. Here is what the current/voltage relationship would look like in an AC-inductive circuit.

You see the current is 90 degrees behind the voltage, the capacitor just causes the current to lead by an added 90 degrees. The waveform with the capacitor added will show a single sine wave like a resistive source would.

These transformers make an excellent supply, when three or more are used, for a medium to high power Tesla coil.

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