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Harmonic Filtering Resistor

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Harmonic Filtering Resistors

Protect Your Power Distribution Equipment

Filnor, Inc. is the reliability leader in the power resistor industry. We provide complete technical assistance in order to meet your specifications. Filnor resistors are used for AC/DC motor acceleration, dynamic braking, ballast, load bank, neutral grounding, harmonic filtering, and transit applications.

harmonic filtering resistors

Harmonic Filter Resistor Assembly

harmonic filter resistor

Harmonic Filter Grid Resistor

Ordering Information Required

• Motor nameplate data (Include secondary data if AC wound rotor)
• Values required per step (Ohms & Amps)
• Nema resistor classification
• Type of controller used and/or wiring diagram
• Terminal designations
• Enclosure type (NEMA 1 or NEMA 3R)


Harmonics are distortions of the sine wave which is provided by the local power company. These distortions are usually produced by electrical equipment that utilize the family of semiconductors known as thyristors (diodes, SCR's etc). Harmonics are classified as being even multiples of the 50 or 60 Hertz base frequency, which makes the second harmonic frequency 120Hz and the third 180Hz.


Prime suspects when evaluating an industrial setting are arc welders, induction type furnaces, variable speed drives and electronic lighting ballasts. To a lesser degree, machines such as computers, ups systems and the usual office machinery may also cause harmonics if they have switch mode power supplies.


The harmonic distortion may involve higher than normal peak voltages and currents which can cause premature failure of devices such as motors, transformers, circuit breakers and switchgear through insulation breakdown, excessive arcing and overheating.


By carefully analyzing the affected facility, the qualified Filnor Engineering staff can determine the best solution to eliminate the harmonics and condition the facility power system. By determining the potential causes of harmonics in the setting, and by examining the facility electrical prints, the proper resistor configuration can be developed. Harmonic filters are the best solution to harmonic distortion. Filnor has a wide variety of harmonic filters to choose from in order to minimize inductance and of course, cost.

Harmonic filters are only one piece of the power system puzzle. To properly condition the system, more active components such as capacitors and reactors may have to be used as well.

The stainless steel resistors may be housed in Nema 1 through Nema 3R enclosures with a standard finish being epoxy powder coat and alternates including, mill galvanized, aluminum and stainless steel. Options include a host of instrumentation, input/output bushings, bottom stands for elevating the unit and forced air cooling.

Contact Filnor, Inc. for more information on harmonic filtering resistors.