High voltage safety

groundinghigh voltage

I remember having seen microwave ovens without the earth connection.

My first question is :
Is it correct that if you touch the MOT transformer chassis, but leave the other terminal floating in air without touching anything, you won't get a shock? Since there is no path for the current to flow back to the other terminal.

My understanding is, before touching the secondary winding, the whole secondary is floating, so the whole secondary winding is like a capacitor in air. Now when you touch one terminal of it, the current in the whole secondary winding has no other source, so only a tiny amount of charge flows through you body to bring the terminal you touch on the secondary to ground voltage, 0V. So, in conclusion, it's safe to touch a floating HV transformer as long as the other terminal is well insulated.

But that doesn't seem right…

In reality though, perhaps the secondary winding is not totally insulated from the core, so part of the HV in the second winding can arc to the core then arc to the mains, which flows through the ground and complete the circuit, which gives a shock?

My second question is :
Suppose for safety reasons I grounded one terminal of the MOT transformer. How do I check if the ground wire really works (i.e. it is really connected to the metal plumbing below where I stand?) My friends says to connect the chassis to a water puddle on the floor through a resistor and use the multimeter to measure the voltage between the resistor. Is that the usual way it's done?

I want to construct a sputtering chamber, the chassis should be grounded, while inside the chamber there will be a high voltage electrode. Using a flyback transformer or a MOT, the high voltage can be generated, but I'm still not comfortable connecting one terminal to the chassis.

Best Answer

I'm not a HV guy.
I'd never touch part of a HV circuit while it was powered. (at least on purpose, we all make mistakes.. 5kV across my finger once.) Disconnect the power and then short all the nodes to ground with a grounding rod.

This says that one of the secondary taps is already connected to the core.

RE: Checking ground connections. Sticking the transformer is a puddle of water sounds like a crazy idea. (Are these people really your friends?) I certainly wouldn't do it with the tranny under power. If measuring the resistance with a DMM is not good enough for you. Then I might get a low voltage DC bench supply, push current to ground and measure the voltage drop.

Above all be safe.

Edit: Just an addition,

I was thinking about some current limit for your circuit. (A big inductor as in link above, or an active thing.) How much current does DC sputtering need? (Do I understand that you are bending the current around with magnets?)

And if you wanted to check for HV before you touch something you could make a little probe with an led and resistor. (100k or so?)