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Electronic neon transformers entail different installation requirements.
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For more than a decade, electronic neon transformers have operated indoor signs. However, they've overcome most of their "childhood" problems -- compatibility issues between microelectronics and high voltage often led to reliability issues -- and are increasingly used for outdoor applications.
But, simply changing an existing installation from a magnetic to an electronic transformer may end in disaster. Thus, this month's column answers frequently asked questions and tells how to avoid mistakes when installing electronic neon-power sources.
Fire and water
Electronic neon power supplies operate at high frequency and high voltage. Physical laws governing direct current (DC) are easy to explain; alternating current (AC) -- think three-phase, power factor and such -- require lengthy discussion. High-frequency circuits are almost impossible to explain in simple terms. As such, most electricians perceive that high-frequency circuits carry a black-magic aura.
However, they're not too difficult to understand. Most electricians are indoctrinated with the basic rule, "Grounding makes the circuit safe." For this reason, electrical wires are installed inside grounded, metal enclosures and conduit. Conversely, high-frequency, high-voltage electricity must be kept far from any ground or metal.
Why is a practice that's fundamental to one electrical system hazardous to another? We're not addressing different kinds of electricity; their physical laws are the same. However, AC's general properties are dictated by its frequency, measured in hertz (Hz). The higher the frequency, the more easily energy radiates into space around the conductor. Radio transmission frequencies typically measure several million Hz. The higher the frequency, the more easily energy radiates into the surrounding space.
Obviously, in signage applications, we want to harness this energy into light in our neon tubes, and not allow it to radiate from the power supply into space. Thus, the guidelines for neon systems powered by electronic transformers aim to curtail radiation from the power supply into space. Safe installations are rooted in knowledge of high-frequency, high-voltage properties. $image1
Capacitance
I've discussed the neon-sign capacitance issue before (see ST, April 2001, page 36; October 2001, page 28; and January 2003, page 18), and I'll summarize it again.
Every conductor can become electrically charged. Thus, electrons repel each other, and they accumulate on the conductor's outer periphery. A stronger charge attracts more electrons, which packs them more tightly together. The tightly packed electrons subsequently "push" against each other. This "pushing" of electrons charges a conductor.
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