FAQ - Neon Transformer internal grounding

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Richard Hull
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FAQ - Neon Transformer internal grounding

Post by Richard Hull »

All commercial, metal cased neon transformers are secondary grounded to the case!
All older commercial neon transformers are current limited via a magnetically shunted transformer core.
The lowest voltage, stock 30 ma standard neon xfmr is 3KV
In general the following are standard voltages found in the classic 30 and 60 ma rated neon xfmrs.

3kv
4kv
4.5 kv
5kv
6kv
7.5kv
9kv
12kv
15kv

All 3-6 kv transformers are pretty much single ended grounded coils in relatively small metal cases ususally with two sunken insulator wells. While they may have two knobs or "wells", one is at case ground. Depending on your use for these lower voltage neons, it would be wise to know which well or knob is at ground.

In general, all 6kv to 15kv transfomers are split, two coil seconadaries with center tapped grounds and the HV from each coil is brought out to an insulating HV knob

Note: there can be a slight chance of variation in the 4.5-6KV range where either dual or single coils are found. You will need to ohmmeter these secondaries output knobs relative to the case to find out what you have.

The classic large metal cased "oil burner" or "furnace" transformer is 10kv @ 23ma and also has a split two coil, center grounded secondary. Oil burner transformers have been seen as low as 7.5kv, but are very rare.

All of the above is for common, older, metal cased, neon sign, commerical units.

All modern stuff that is open frame or one-off cheap chicom neon and junk oil burner plastic cased stuff is a crap shoot and unless you are willing to play with them and figure them out, you might want to avoid them.

I still see the older, heavy, metal cased neon transfomrers at some hamfests for as little as $20.00 each, but prices are rising as these old reliable, shunted transformers are replaced by solid state units that are more finicky and subject to damage in the abusive amateur TC and HV world.

New prices for the these older units were around $150.00 for a 30 ma unit and $250.00 for a 60 ma unit.

Last year we had a guy at my HEAS fleamarket dumping a couple of the 30ma oldies for $10.00 each!

In closing, it must be remembered that the neon sign transformer can be ideal for a demo fusor and getting your first plasma, but will not be suitable for a fusing fusor due to its magnetically shunted core and lower voltage output at load up.

For more details on the loading factor of shunted neons go to my post at

viewtopic.php?f=19&t=7945#p57349

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.
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