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Re: [TCML] frailty of NSTs

Hello all,

Happy Easter to those who celebrate.

What is it about NSTs that makes them so fragile? I suspect it is the current through a secondary wound with
inadequate wire size.

I have a couple of E I laminate core transformers 1.25 inches wide by 3 inch stack, six by seven o.d. that I am considering rewinding. I believe that winding separate primary and secondary would be better
than secondary over primary or even primary over secondary.

Any thoughts on this?


I think the so-called "fragility" is only in that their insulation isn't designed to withstand very much excess voltage such as can be created by resonance or near resonant capacitive loads; in other words you can short one if you do something stupid. I'm not sure that they're much different from ordinary small transformers in this regards. Power line transformers are designed to take high surge voltages but that's a different type of device.

While in normal sign service the secondary voltage of an nST is usually limited by the tube drop to significantly lower values than the open circuit ones I think their open circuit life is pretty high, probably comparable to other transformers of similar size. I ran one open circuit outdoors rain or shine for about three years in an electric fence application [very dangerous of course] and it certainly survived unscathed. This particular transformer [9 kV, 60 ma] had been shorted earlier in TC service when I accidently opened the spark gap too far but I had restored it by just remelting the tar at the shorted end with a heat gun, indicating that the short was external to the winding.


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