When the voltage or current wave in an electrical circuit becomes distorted, electrical harmonics occur. Harmonics can interfere directly with electric motors and telephones, and indirectly with anything drawing power from the affected circuit. The effects of harmonics on home electrics can range from damage due to overvoltage, intermittent operation, heat damage from overheated wiring, and malfunctions in computers and computer-controlled electronics.
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Switch Mode Power
The most common source of electrical harmonics are "Switch Mode Power Supplies" typically found in personal computers, dimmers, steroes, radios, fax machines, televisions and laser printers. The SMPS functions as a power converter, taking electricity from the power grid and powering an electronic device, but the non-linear loads they create can cause the distortions that cause electrical harmonics, even under optimal conditions.
If SMPS devices are on the same circuit as lights and other utilities, the distortions will affect everything operating on that circuit. When this happens, the effects of electrical harmonics are most noticeable. The affected circuit will heat up, causing incandescent lights to blink or electronics to malfunction, and may trip the circuit.
SMPS devices may interfere with other devices that share a ground wire. If electrical harmonics are being generated, and using a dedicated circuit is not an option, the problem may be overcome by installing a separate ground on outlets that will power SMPS devices. Use of an oversized "neutral" may also prevent the overheating problems that can be associated with ground wires on SMPS devices.
The wiring in newer homes is designed with personal electronics in mind and should not be notably affected by electrical harmonics from SMPS devices because of the presence of harmonic filters acting on the electrical mains. These filters act like a short circuit at certain frequencies, preventing electrical harmonics from affecting other sections of the main electrical circuit. Older homes that were wired before computers and entertainment systems became common in the household will often lack adequate filtering of the frequencies at which harmonics occur. They can be retrofitted, but that would require the work of a licensed electrician and could be expensive.
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