Original poster: David Speck <Dave@xxxxxxxxxxxxxxxx> John,Probably the best approach would be a SPDT vacuum relay. These come up regularly on eBay, and are available in a variety of voltage and current ratings. The military ones are rated at 26.5 volts, but usually work on 24 V without complaint. Patience is a great virtue in this search, as sometimes, they go for next to nothing, and other times, identical pieces bring crazy prices. Try searching for "vacuum switch*" or "vacuum relay*"
Connect the center switch connection to the grid, the normally closed terminal to ground, and the normally open terminal to the 25 kV supply.
If you are concerned about reliability, you can use two separate relays in parallel. Then, either relay could ground the grid if the other failed. I assume that there is not a lot of capacitance on the grid system. If there is, you might need to put a current limiting resistor in series with the ground path to keep the discharge current within the ratings of the vacuum relay.
Dave Tesla list wrote:
Original poster: <alderhood@xxxxxxxxxxxxx>I am looking for a failsafe switch that can switch a grid between the 25Kvac power supply and ground. We are talking about very small amperages .The switch will be functioning as a safety to protect maintenance people and not for control purposes. I need for it to have a coil preferably 24VAC that will cause the grid to shift to ground on de-energizing. It seemed to me that this was simple at first but I may have too many trees blocking my vision of the forrest. A little help please and contact me directly as well as on the list.Thank you, John Alderman alderhood@xxxxxxxxxxxxx