Proper Maintenance of an Automatic Transfer Switch (ATS)

In an emergency power system, an automatic transfer switch (ATS) ensures that critical loads maintain power–transferring from utility power to an emergency power source when the normal source voltage falls below preset limits.

The ATS is often referred to as the brains behind an Emergency Power system, continuously monitoring the power coming from the utility. When power goes out, the ATS automatically signals the generator to start. It also monitors the generators voltage and frequency for proper operation prior to transferring critical life safety loads.

The ATS is a critical component of any emergency power system. Like all electrical equipment, however, routine care is necessary to ensure consistent operation. Annual ATS maintenance is not optional, it is required.

Mechanical integrity is a must

First, check for mechanical integrity. Keep an eye out for loose, broken, or badly worn parts. Look for any deterioration of wiring or insulation caused by abrasion, wear, or cuts. Melted plastic, discolored metal, or a burning odor could be indications of overheating.

Next, check that the ATS is clean and free of obstructions. At most ATS locations, it’s common to find an accumulation of dust, dirt, or moisture. The ATS is best cleaned with a vacuum, a soft brush, or cloth, avoiding compressed air or a blower as debris can become lodged in the components, ultimately causing damage down the road.

Next, verify the appropriate lubrication on moving, current-carrying parts. Lubricate the transfer solenoid mechanism that transfers the power source from the utility to the generator. It’s also important to check the main contacts and tighten the control wires. Most ATS failures are due to a lack of maintenance and lubrication.

Dropout, pickup

Automatic transfer switches continually monitor both the voltage and frequency of the utility and alternate power sources.

One criterion for initiating the transfer of the load to the emergency source is the dropout voltage. When voltage dips below a predetermined level, the automatic transfer switch controller will detect an unacceptable power source, thus initiating the transfer of the load to the emergency source.

Alternately, the pickup voltage is the criteria for identifying when the source of power is acceptable. The pickup voltage is a prerequisite for re-transferring the load back to the primary source—typically utility power. Pickup voltages are set to a higher level than dropout voltages, which avoids unnecessary transfer switch cycling.

Both the dropout voltage and pickup voltage can be calibrated to suit the specific needs of a given facility. Calibrating the dropout and pickup voltages to ensure precise operation is an essential part of ATS maintenance.

Time is of the essence

Unnecessary cycling of an ATS can cause unwanted wear and tear. To prevent excessive cycling, an ATS incorporates timing delays to assess a power source’s stability. After detecting a low-voltage situation, the ATS monitors the utility power source to verify if the problem is ongoing or just a momentary anomaly. If the low-voltage situation continues, the ATS will signal the generator to supply emergency power until the primary power source has returned to 90% of its rated value and has returned as a stable power source.

As with other components of an ATS, the time delay features should be tested and calibrated to ensure proper operation. Finally, be sure to check the engine start features to guarantee that when the ATS signals the generator to start, not only that the generator started, but that it is operating as its proper voltage and frequency ratings.

Trust the experts

To safely install, modify, and maintain automatic transfer switches, specialized training is required–which many electrical contractors lack. EPC Electric follows strict safety protocols to protect the wellbeing of our technicians, our client’s personnel, and the general public. We service all brands and types of emergency power systems, and our work adheres to National Fire Protection Association (NFPA). EPC has spent 37 years in business working on Automatic Transfer Switches and has proven the experience and knowledge to earn your trust in maintaining ATS needs.

Call EPC today at (800) 540-0707 to get started.

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