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BUYING A USED NEON SIHN TRANSFORMER

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LAN_403

radioman

Sat Oct 01 2011, 01:53PM

Registered Member #3026 Joined: Fri Jul 23 2010, 02:46PM
Location: Los Angeles, California, U.S.A.
Posts: 54

Hi Everyone,

I know that a NST with ground fault protection is no good for a Tesla Coil. I am going to buy one from a local electronic surplus store. How can I be sure that it does NOT have the ground fault protection? Is this feature always marked in some way on the case?? I sure hope so!

Thanks,
JM

Daniel Kramnik

Sat Oct 01 2011, 02:22PM

Registered Member #3885 Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94

GFI protection is always mentioned on the case of the transformer (I think it's a legal thing), but just in case you're unsure, try drawing arcs and seeing what happens.

Killa-X

Sat Oct 01 2011, 04:49PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

When I went neon shopping at a pallet with 30 transformers, 80% of them said "Secondary Balanced Mid-Point Ground" None of them had the word GFI or Ground Fault Interruption. It can be arced, dead shorted, etc and it will never turn off.

Like Daniel Kramnik said, Just try arcing it.

Herr Zapp

Sun Oct 02 2011, 12:50AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

radioman -

All NSTs incorporating an "internal GFI" will be marked on the nameplate "UL2161 Secondary Ground Fault Protected" or similar wording.

The internal GFI will shut down input power to the transformer when it detects a secondary leakage current to ground of 15ma or greater.

Herr Zapp

Adam Munich

Mon Oct 03 2011, 01:01AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Not always herr zap...

"Because underwriter's laboratories had nothing better to do they published the UL2161 standard; a rule that requires all new NSTs to contain a secondary ground fault interrupter. This means that an sGFI circuit must be included in all new transformers --a circuit that will turn off the NST if a short circuit is detected. Since an arc is for the most part a short circuit this is bad news for experimenters. However, the UL2161 includes one exception for transformers with socket-type HV terminals. These transformers must bear the "recognized component" (backwards RU) symbol. If you encounter a socket-type NST that bears the RU symbol yet lacks the UL symbol there's a very good chance that it's not sGFI protected."

Pulled from my site since I'm lazy.

Herr Zapp

Mon Oct 03 2011, 04:56AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Grenadier -

I didn't make any mention of either UL's "recognized component" symbol, or the standard "UL Mark".

If the neon sign transformer has achieved UL certification, and HAS an internal GFI, the nameplate WILL make some mention of UL2161.

I think you may be confusing the UL marking requirements with UL "application" requirements. UL has provided a a number of exceptions (at least 5) where a non-GFI-protected NST can be used in neon sign applications, IF certain requirements are met.

Here's some information on UL2161 from the General Electric Lighting Solutions website. (GE used to manufacture NSTs, but now focuses on more modern lighting technologies like LED, HID, high-efficiency fluorescent, etc.)

"The UL 2161 standard was developed primarily to reduce neon-fire hazards. To encompass all cases and avoid needless regulations, the standard requires all neon power supplies, whether magnetic or electronic, to incorporate secondary ground fault protection (SGFP).

But there are some exceptions from this general rule, as follows:
1) If the maximum output current of a neon supply (magnetic or electronic) does not exceed 15mA rms between any terminal or ground (at any voltage).
2) If the output current does not (even in short circuit) exceed 30mA rms, and
a) The open-circuit output voltage is less than 3001 volts rms at an output frequency of less than 100 Hz (magnetic transformers) or
b) The open-circuit output voltage is less than 2001 volts rms at an output frequency of more than 100 Hz (electronic power supplies).
3) If the secondary coil is isolated from any other part of the transformer and the output voltage between any combination of output terminals does not exceed 7,500 volts rms.
4) If the transformer has no other means to connect its output than integral electrode receptacles (housings) recessed into the transformer body, and all tubes in the installation are interconnected without using GTO cable (for example, with double-housing type connectors).
5) If the power supply is labeled "cold-cathode supply" (intended for use in a general illumination system with cold-cathode discharge tubes according to Article 410 of the National Electric Code [NEC])."

One interesting factoid that UL2161 allows a residual "test voltage" to be present on the HV output terminals AFTER the GFI has tripped. This "test voltage" can be as high as the transformer's input voltage, but current is limited to 0.5ma.

Herr Zapp

Tetris

Mon Oct 03 2011, 10:12PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

mine is franceformer. lots of others' are too. I am pretty sure franceforemers are mainly not gfi

Adam Munich

Tue Oct 04 2011, 10:51AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Franceformer is a company, subject to UL regulations.

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