Original poster: "Gerry Reynolds" <gerryreynolds@xxxxxxxxxxxxx> Hi Todd,Yes. There is a simple procedure for setting the safety gap length. Some will advocate a setting of a fixed gap length, but I don't recommend this as the actual breakdown voltage is affected by the electrode geometry and the altitude you are operating at (among other environmental factors). Many would recommend disconnecting the TC primary, tank cap, and main spark gap from your NST so the only load the NST sees is the filter and the safety spark gap. You would then set each gap (one for each NST bushing) so it would just barely not fire with this almost "no load" condition. Start with a small gap size and power up the NST and see it arc across the safety gap. Power down, unplug from the power source, and then increase the gap a little. Repeat this procedure until the gap width is just barely too wide to arc. This will be your setting (one for each bushing). At this point the safety gap will arc if the voltage across the gap ever gets larger than the "no load" output voltage of the NST. If you are using a variac to drive the NST, set the safety gap with the variac at the maximum output voltage that you would want to operate at. Most would do the setting with a maximum 140Vac output from a 0-140Vac variac when 120Vac is feeding the variac. Once set, leave it alone. If during operation the safety gap fires too often, this would indicate that your main static spark gap is set too wide. Reduce the main gap setting until the safety doesn't fire or fires only occasionally.
Gerry R.
Original poster: "Todd Reeve" <todd.reeve@xxxxxxxxxxxx>I am putting together a Terry filter for my coil as we speak. I realize how important the gap width is but I am unsure how to determine the proper gap width.I am using a 15kV/60mA nst. Can anyone suggest the proper method to determine the gap width?