|> | Michael Shaffer wrote: |> | Anyways, shouldn't the GFCI of tripped or not? |> | |> | |> | Nope. |> | |> | The welder is essentially an isolation transformer. The GFCI is only |> | looking for a ground fault on the primary side of the transformer. You |> | got a shock from the secondary side, and a primary GFCI won't do a thing |> | to prevent it, as you discovered.... |> | |> | Bob Weiss N2IXK |>
|> Is it a total isolation? Or is there a ground-to-ground connection | between |> primary and secondary? |>
| | It's total. But that is not relavent to the GFCI issue.
It can me. If there is a ground or neutral connection between primary and secondary, it can form an additional path, creating a common ground for the otherwise separately derived system. A ground fault can then flow from a hot wire on the secondary, to real ground, to the ground or neutral wire, to the power connection coming into the transformer, and over the ground wire between primary and secondary completing the circuit. It is then a potential shock path. If the ground clamp comes loose on the working object, you may still have a circuit if that object touches ground in some way (like through human contact).
If that connection is not present, you can be raising the voltage float on the secondary system due to capacitive coupling. Think of it as being in a ground fault loop in series with a capacitor.
Ground fault protection of a welding system would be a good idea. It can potentially be a difficult design to protect it, given the way it is used. But it would not be impossible. For example, the ground can be connected between primary and secondary, and a current sensor placed on it to check for any fault currents at the 4 milliamp level to protect humans. And additional current sensor on the actual welding leads could smooth out the current spikes first, and then see what difference remains.