Maintenance contracts can improve reliability, safety

Neglecting routine tasks increases the probability of unscheduled downtime.


A proper maintenance system will deliver quality, uptime, and safety. Those three criteria are especially important when discussing power distribution systems. Photo courtesy: Schneider ElectricElectrical equipment and power distribution systems have never been designed to be or intended to remain perpetually energized. All electrical power distribution systems will experience some type of electrical power interruption, whether it will be for scheduled maintenance or unscheduled downtime due to an electrical fault or inoperative equipment.

No matter the demands or insistence of management, 100% power system reliability is never possible because individual electrical components that make up a power distribution system will become inoperative at some point during the lifecycle of the system.

A lack of routine cleaning, preventative maintenance, and equipment testing will greatly accelerate the probability of unscheduled power outages or inoperative electrical equipment. In addition, electrical workers are much more likely to be injured during emergency repairs than while performing routine preventative maintenance.

In general terms, “reliability” is a property of a power system that describes the likelihood that the same system will successfully operate or perform as designed, constructed, and intended. More specifically, “reliability is the statistical probability that the system will be able to perform its intended mission.”

The “notion of reliability” is more of a mathematical probability than an actual physical condition and is determined from the combination of statistical dysfunctional or inoperative rates of individual components and the configuration of the power system to which they are applied. For example, the simplest power distribution system consists of two protective devices connected in series (i.e., a main and feeder overcurrent protective device) to supply power to a load.

While one might initially think that two 90%-reliable devices in series would yield a 90% reliable system, in fact, the system reliability is the product and not an average of the reliability of the two devices, or 81% in this case. Drop the reliability of one device to 70% due to lack of maintenance and total system reliability plummets to 63%.

In addition, it is important to note that any “notion of reliability” is also a function of the complexity of a power distribution system. The magnitude or level of complexity (C) of any power distribution system is a function of the number of individual components and parts (P) that are employed to assemble and construct the final system such that Cx = Px.

Simply stated, a greater number of assembled components and parts will equate to an exponentially more complex system. The greater the complexity of a power distribution system, the less reliable it can become. If a complex power distribution system is not routinely maintained or serviced, then there should not be any rational expectation of reliability as electrical equipment and the system ages.

Preventive maintenance yields positive return

A regularly scheduled electrical system preventive maintenance program is intended to detect, repair, or replace affected electrical components, parts, or equipment before they lead to catastrophic damages, significant power interruptions, and loss of business functions. According to studies published by the Hartford Steam Boiler Insurance Company and FM Global, “Electrical equipment failures account for millions of dollars in damage and lost business every year.” 

In fact, lack of a routine preventive maintenance program places a facility in a “run to failure” or “run to breakdown” mode. IEEE Standard 902 cites that “a lack of maintenance eventually results in failures and a high cost to a plant.”

The rate of electrical damage can be as much as three times higher in facilities that do not perform preventive maintenance. In addition, neglecting maintenance and testing may void any equipment warranty (or extended warranty) that is in force as well as negate the terms and conditions of a commercial underwriter’s insurance policy.

It is extremely important to note that any specific maintenance of separate pieces of electrical equipment does not guarantee a completely coordinated and reliable electrical power distribution system. A comprehensive and routine preventive maintenance and testing program should incorporate all electrical power distribution equipment, regardless of the manufacturer, to ensure that all electrical equipment and components operate as originally designed and intended during their entire expected operational use life. The ultimate goal is to minimize equipment malfunction, power outages, or service interruptions to business operations or services. All studies of electrical maintenance programs show a direct correlation between levels of routine maintenance and the reliability of electrical equipment and the power distribution system.

Adopting a proactive maintenance culture

Transitioning from a reactive “fix only what is broken” culture to creating a proactive routine preventive maintenance model is a long but sound business process. Before any maintenance program is initiated or contracted, it is strongly recommended that the facility’s management contract and commission the services of a licensed professional electrical engineer to perform short circuit analyses, a time/current coordination study, and an arc flash analysis of the entire electrical power distribution system.

These studies will ensure that the existing electrical equipment is properly rated, set, and labeled. There is wasted value in spending limited maintenance budget and resources to clean, maintain, and service electrical equipment that is later determined as needing to be replaced or removed from service.

In some circumstances, a power system risk assessment is recommended prior to beginning a preventive maintenance program. The risk assessment can reveal safety concerns and poorly maintained equipment, as well as the negative effects of harsh environmental conditions such as elevated temperature, moisture, dirt, polarized dust, and other contaminates on electrical equipment.

A risk assessment provides valuable information concerning the “present state” of an electrical power distribution system and its associated equipment, its functionality, and reliability relative to the present needs of a facility’s operations. (Note: Business functions and operations change much faster than power distribution systems. A 20th century power distribution system might be inadequate for the needs and requirements of 21st century sensitive electronic loads.)

A key feature of a power system risk assessment is the hazard vulnerability analysis, which prioritizes the recommended corrective actions based upon safety and the criticality of a facility’s operations. A power system risk assessment facilitates the development of a proposed maintenance schedule specific to a facility’s power distribution system. In addition, cost estimates are provided to help management develop a budget to carry out the maintenance activities.

Qualifying maintenance contractors

An industrial facility’s electrical infrastructure typically consists of service entrance switchgear and switchboards, distribution panelboards, power panels, motor control centers, various sized circuit breakers, distribution transformers, fused disconnect switches, PDUs, UPS units, battery banks, standby generators, paralleling switchgear and switchboards, and automatic transfer switches.

Therefore, very few electrical maintenance or contracting companies can perform all of the required maintenance activities for an electrical distribution system. A professional electrical engineer can assist facility management with the selection of a qualified electrical maintenance contractor.

Impact on workplace safety

A common cause of accidents is workers being placed in harm’s way. Consider this scenario: A piece of equipment breaks. The maintenance worker may have to enter a confined space; be exposed to dusty, cluttered, or moist environments; and may not have the proper tools to repair the equipment. The worker might be inclined to improvise to perform a specific task at the expense of safety. Properly planned maintenance activities provide for a greater safety environment and lower the risk to the maintenance worker and those who might also be working in the area.

As noted earlier in this article, no electrical equipment is designed and intended to operate in perpetuity. All electrical equipment will eventually exceed its reliable use life and will become dysfunctional or inoperative. However, an effective and routine preventive maintenance program can address accelerated deterioration before the equipment becomes damaged, inoperative, or unreliable.

Exxon-Mobil conducted a study on maintenance-related accidents. The findings revealed accidents were five times greater when workers were working on damaged electrical equipment than when they were on planned corrective jobs.

Another very important aspect of how reliability affects safety is in reducing the potential for an arc flash event. Because arc flash incident energy can only be controlled by the protective devices in a system (i.e., circuit breakers, fuses, and protective relays), the regular inspection and maintenance of these components is critical to the reduction of arc flash energy and hazards.

The device’s operating time is critical to reducing arc flash incident energy. Any arc flash analysis assumes that existing protective devices will operate in a pristine condition based on the device’s original OEM time current curve. If the protective device is not in a functional and well-maintained condition, then the opening times can vary considerably from the original trip curve. In some instances poorly maintained devices will not operate as designed and intended.

When these conditions occur, the incident energy during an arc flash event will become unpredictable. Attention to arc flash safety raises the bar with regard to the importance of maintaining and testing equipment to be sure that it will operate properly "on the curve.”  

Waterer is an engineering fellow and consultant for Schneider Electric Engineering Services.

Establishing a maintenance contract

Note: This section references low-voltage equipment only since it is predominant in electrical distribution systems.

This has been mentioned before but is worth repeating: Any specific maintenance of separate pieces of electrical equipment does not guarantee a completely coordinated power distribution system. Therefore, when establishing a preventive maintenance program, it is strongly recommended that a detailed scope of work be drafted regarding the equipment and types of testing and maintenance to be performed.

This helps to ensure the maintenance service provider and facility management are in agreement with the scope of work to be performed. Recommended electrical equipment to be incorporated into a regularly scheduled preventative maintenance contract should include:


  • Monitor equipment
  • Switchboards and panelboards
  • Uninterruptible power supply systems
  • Metering equipment
  • Motor control centers
  • Busway
  • Protective relays
  • Transformers
  • Stand-by generators and associated service entrance switchgear
  • Automatic transfer switches
  • Optional paralleling equipment.


The maintenance contract also needs to clarify that the scope of work meets:


  • Local code requirements and manufacturers’ recommendations, and
  • Accepted industry standards for electrical workplace safety.


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