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Neutral noise poses immense menace
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14/03/2008
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Electrical noise coming down the neutral wire can cause expensive instruments and machinery to take momentary timeouts, and long-term damage to microprocessors – severely curtailing the lives of controllers.
It is easy to sense, but requires taking proper steps to eliminate, if it is not to cause serious trouble. Surge suppressors and UPS units, seen as protection for most kinds of equipment do little or nothing to prevent it.
At a recent event in London, Rob Morris of Powervar performed a convincing demonstration by attaching a hair dryer to a main supply, then probing the live and neutral sides of the supply with a Power Probe 115 high pass filter. This revealed severe electrical spikes on both the live and neutral sides of the supply. He said that the signals on the neutral side – common mode noise – caused particular problems because microprocessors normally take their 0V logic references from the incoming neutral line. While he described pulses large enough to cause “destruction” of electronics as “relatively rare”, he said that degradation, resulting in point of sale units made by one of his customers having their average working lives reduced from 10 years to 6.5 years, was not uncommon.
A search on the Internet reveals that there is a widespread awareness of the problem among electronic specialists, while there are still makers of equipment who are blissfully not aware.
Powervar conditioners, he said, possess a combination of surge arrestors, an isolation transformer and a tuned filter.
“People used to avoid this problem when they all used linear power supplies, but when they went to switch mode supplies, they effectively designed out mains filtering,” he said. “We put the filtering back in.”
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Author
Tom Shelley
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