Harmonic problems in a Casino

By : Arteche Power Quality Phone: 1-262-754-3883 (USA)

Objective: Redure third harmonics

A casino, located in Michigan, had 1000 slot machines and was planning an expansion that involved 500 additional slot machines. Their local electric utility measured voltage distortion of nearly 5% THD-v, plus the casino experienced interference on their CCTV security monitors. To improve the operation of their security systems and to meet the utility power quality requirements, they needed to solve the harmonics problems before adding 500 more harmonic
producing slot machines.

Problem : Harmonics caused by 1-phase power supply

Due to the accumulated effects of numerous switch-mode power supplies, (used in computers, video games and slot machines) the casino was experiencing several power quality issues:

  • Harmonic voltage distortion was about 5% THD-v .
  • Branch circuit current distortion was about 60% THD-i.
  • 3rd harmonic current was as high as high as 50%.
  • Neutral ground voltage measured several volts.
  • UPS system fluctuations
  • Surveillance camera distortion
  • Corruption of access control data transmissions

The Solution: Adding a third harmonic filter  (THF)

The Third Harmonic Filter is a series connected filter that is specially designed to minimize third harmonic currents in 1-phase circuits. In addition to reducing the 3rd harmonic by as much as 80-90%, this filter can also reduce the 5th, 7th and 9th harmonics. The THF filter is ideal for 3-phase, 4-wire power systems as found in casinos, office buildings and other commercial applications.


The THF-60-0020-120-N1 is a branch circuit current rated filter and proved to be effective and convenient for this application which had as many as eight slot machines supplied from a single branch circuit. THF filters can be hard wired into the circuit and should be selected based upon the current rating of the branch circuit protective device.



  • 3rd harmonic current was reduced to less than 10%.
  • Reduced 3rd harmonic current on neutral.
  • Reduced transformer load and temperature.


As shown below, the filter can be located in the pedestal beneath the slot machines and wired in series with the branch circuit conductors that supply several (typically 2-8) slot machines.

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