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Useful Life Expectancy

Updated: Dec 16, 2019


It is not uncommon to see electrical equipment that has been in service for over 40 years still functioning without issue or cause for concern, but how can you tell how long equipment will actually last? When determining life span for electrical equipment, most electrical distribution equipment’s useful life expectancy falls into the 20-30-year range assuming manufacturer recommended ideal operating conditions (max ambient temperature of 40 °C with an internal temperature rise not more than 65 °C, low humidity levels). The manufacturers listing of 30 years is based on insulation degradation under ideal conditions, however, environmental conditions can have severe impacts on insulation quality.

Formal bodies (UL, NEMA, FM, NFPA, etc.) do not have standard expectations for equipment life expectancies. NEMA cites proper application, environment, and maintenance are all significant impactors on equipment lifespan. The biggest contributors to equipment lifespan are environmental: temperature, humidity, and ventilation. However, other factors including installation quality and regular maintenance are the most significant.

Environment – Temperature:

High temperatures are arguably the biggest contributor to degrading equipment, the IEEE and ANSI standards suggest limiting any electrical insulator to a max temperature of 105 °C. This number is the sum of max ambient temperature of 40 °C with an internal temperature rise not more than 65 °C. Anything beyond that results in degradation of the insulation, which can have catastrophic results by causing a potential short circuit in the system.

Thermal Infrared scans of equipment can uncover areas that may warrant attention and can reduce the number of catastrophic equipment failures as well as the resulting facility shutdown. ANSI/NETA MTS, Standard for Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems state that:

  1. A temperature difference as low as 1 °C to 3 °C indicate a possible deficiency and warrants investigation.

  2. A temperature difference of 4 °C to 15 °C indicate a deficiency and repairs should be made as schedule allows.

  3. A temperature difference of 16 °C or higher indicates a major deficiency and repairs should be made immediately.

Increased Temperature Due to Loose Conductor Connection at Circuit Breaker

Environment – Humidity and Ventilation:

Most electrical equipment located within an electrical room or closet has a NEMA rating of 1, meaning it has an enclosure acceptable for indoor use in a dry environment, provides a degree of protection to personnel against access to hazardous (energized) parts, and offers a degree of protection of the equipment from ingress of solid foreign objects (falling dirt, dripping water, etc). However, this does not provide protection against humidity. Most readers may understand the importance of conditioning / ventilating the space based on the known fact that water and electricity do not play well together.

Elevated humidity levels can cause oxidation of equipment components, degrading electrical connection and causing components to heat up, deteriorating surrounding insulation. Extended high humidity situations can cause mold to form on insulation and degrade any areas affected. In extreme situations condensation within electrical equipment can cause a short circuit.



 Corrosion at Mechanical Connections

Installation Quality:

The way equipment was installed can be a large contributor to how long the equipment may be in service. Some questions you may want to consider include:

  1. Was the equipment installed level, on a concrete maintenance pad?

  2. Were all ventilation covers removed prior to putting it into service?

  3. Does equipment have proper clearance to maintain adequate ventilation?

  4. Did the equipment fit together neatly, with proper alignm