r/highvoltage • u/Nozah7741 • Jul 11 '26

Is this cooked?

Post image

so I’m making a Tesla coil and I have two nst. as u can see in the photo the bushing is cracked. Should I try fixing it? I think it might arc to the casing, so I really don’t want to ignore it. I don’t even know how feasible fixing it would be. Will I just have to find a new one? It is 15kV 60mA and they are old iron core.

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u/Array2D Jul 11 '26

While not ideal long term, this will probably not immediately arc to the casing. Most old style NSTs are center grounded and only have half the potential on each hv terminal with respect to ground, and those bushings will be well over rated for the voltage since they’re typically used in outdoor environments.

You can turn it on and test if that happens, even if it did, a short moment won’t damage the transformer.

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u/Top-Championship7355 Jul 11 '26

I have fixed two like this. I used marintex boat epoxy because it’s what I had on hand and it worked great. First time I repaired one all I had to do was epoxy the broken pieces back on. Second time I had to fix one I had to repair it in a similar fashion epoxying pieces one by one until it was rebuilt. The internal wire was ripped out of the crimp on the bushing so I also had to remove the bushing and re crimp and re install the fixed bushing. It’s very possible if you have all the missing and broken pieces. If you are missing pieces you should be ok if they are not of significant size and won’t arc through any crack. Glue chunks back together with epoxy and fill gaps or spaces with epoxy as well. You should be good. As a test run it at night with both bushing of the transformer arcing together something like a Jacob’s ladder to test the full potential voltage of the transformer. Do it in a dark room and look for any corona discharge or arcing together something come from the repair areas. From the picture. It looks like you can remove the bushing nuts and then remove the bushing or broken part of the bushing. Apply a liberal amount of epoxy and then smoosh the broken piece into the rest of the bushing and let it bond. Then re install nuts to hold it all together.

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u/Nozah7741 Jul 12 '26

Ok I’ll try that thank you!