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Stop Those Zaps From Double Insulated Equipment!

If you have experienced mild tingles or shocks from double insulated equipment, you will want to know how to prevent them. Here's our "Tingle Terminator": a simple solution to this vexing problem. There is no need to gain access inside the equipment and it will not void the warranty.

By John Clarke

Modern double insulated equipment such as DVD players and digital set top boxes (STBs) can give you a mild electric shock.

The experience is not unlike the static zap you sometimes get when alighting from a car in dry weather or from the metal hose of a vacuum cleaner. Such a shock may well reduce your confidence in the safety of the appliance even though there is no inherent fault.

Whether or not you experience such a shock will depend on the installation. But perhaps we need to describe the problem first.

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Compare the difference in conventional (older) style power supplies (Fig.1, above) with the "switch mode" supplies found in the vast majority of modern electronics (Fig.2, above right). In the older style supply, the entire power supply is isolated by the mains transformer but in the switch-mode supply, there are components on the primary side of the high frequency transformer. These can have small leakage currents which can give you a tingle. They're not (in normal circumstances) dangerous. But they are certainly annoying!
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These days most home entertainment equipment is double insulated. This includes most TV sets (CRT, plasma, LCD, projection, etc), VCRs, STBs, DVD players and amplifiers. This means they are powered from the mains using a 2-pin mains plug – one that does not include a mains earth connection. Normally though, such equipment has a metal case or some exposed metal in its construction.

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