How can a CT generate a lethal high voltage when not connected to burden resistance?

A CT is a current transformer. The key Word is transformer. Any transformer has a turns ratio. Take a 480V to 120V transformer for instance. The ratio is 4:1, that is for every turn of wire on the secondary winding, there are four windings on the primary. So, if there are 200 turns on the secondary, there are 800 on the primary. We can reverse that same transformer to make it a step-up transformer. Now we would say it has a turns ratio of 1:4. Lets take that transformer and modify it (in our imagination) to see what will happen. Every time, we will apply 120V to the primary, and measure the output voltage on the 800 turn secondary. We will change the number of turns on the primary each time. First, the original ratio: 200T (turns) : 800T (turns) = 1:4 (ratio) = 120V (input) : 480V (output) OK, that seems pretty obvious. But now lets start removing turns from the primary. Watch the trend of secondary voltage: 100T : 800T = 1:8 = 120 : 960 50T : 800T = 1:16 = 120 : 1920 25T : 800T = 1:32 = 120 : 3840 5T : 800T = 1:160 = 120 : 19200 2T : 800T = 1: 400 = 120 : 48000 Wow, the output voltage for our transformer with a two-turn primary is a whopping 48000 volts! Is it possible to have a transformer with a one-turn primary? That is exactly what a current transformer is! the bus wire that passes through the CT forms a one-turn primary, and the many-turn CT coil forms the secondary. If the secondary is shorted, the secondary reflects the primary current divided by the number of secondary turns. But if the CT is open, the current ratio is now 1:zero (no load), the voltage ratio is the inverse - 1:infinity. So, if the CT is not shorted with a very low resistance, it tries to be a voltage transformer with an extremely high secondary voltage. In practice, the voltage is limited by coronal discharge and/or insulation breakdown of the windings. But it can produce some pretty good fireworks and smoke while it is happening! I once observed a facility electrician at one of my customers industrial plants accidentally cut through CT wiring while it was energized. He thought the conduit was abandoned and he was removing it. That CT wiring easily produced an impressive 2-inch continuous arc. This is why CT's are wired through special terminal blocks that short out the CT when the disconnect is pulled. You should never try to work CT wiring hot, and not under any circumstances if you are not trained and qualified!