top of page

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 alignment?

  5. Were splices done using the correct size splice place?

  6. Does the equipment have the correct number of bolts?

  7. Are all bolts torqued properly?

  8. Proper connection for sufficient metal contact.

Installation quality is important because overloaded equipment or under torqued bolts can also significantly increase the internal temperature rise beyond 65 °C. Overloaded equipment has higher amperage flowing through components and insulation than the rating allows for. Under torqued bolts cause loose connections that result in larger surface areas heat up and degrade surrounding insulation.

Exterior Transformer Installed Using Unsecured CMU


Maintenance is directly related to equipment lifetime. NFPA 70B “Recommended Practice for Electrical Equipment Maintenance” as the name suggests, details guidelines for electrical equipment maintenance programs, including regular visual and infrared inspections, lubrication, cleaning of electrical equipment.

According to NFPA 70B section 4.2.2 “Benefits of an effective Electrical Preventative Maintenance program fall into two general categories. Direct, measurable economic benefits are derived from reduced cost of repairs and reduced equipment downtime. Less measurable but very real benefits result from improved safety.”

NFPA 70B section 5.2 suggests that a maintenance program consists of:

  1. Responsible and qualified personnel

  2. Regularly scheduled inspection, testing, and servicing of equipment per manufacturer’s recommendations

  3. Survey and analysis of electrical equipment and systems to determine maintenance requirements and priorities

  4. Programmed routine inspections and suitable tests

  5. Accurate analysis of inspection and test reports so that proper corrective measures can be prescribed

  6. Performance of necessary work

  7. Concise but complete records

Section 5.3 continues stating that “the following factors should be considered in the planning of an EPM program.

  1. Personnel Safety: Will an equipment failure endanger or threaten the safety of any personnel? What can be done to ensure personnel safety?

  2. Equipment Loss: Is installed equipment — both electrical and mechanical — complex or so unique that required repairs would be unusually expensive?

  3. Production Economics: Will breakdown repairs or replacement of failed equipment require extensive downtime? How many production dollars will be lost in the event of an equipment failure? Which equipment is most vital to production?

When Properly Maintained and Tested – Equiptment Can Be Reliable Beyond Life Expectancy (MCB manufacture date pictured is March 1969)

Proper electrical maintenance can improve a facility’s power quality by helping to identify harmonics as well as any areas that can benefit from power conditioning to help with surges, sags/swells, unbalanced voltages, noise, and voltage fluctuations.


While it’s challenging to determine when electrical equipment will fail, there are many factors that can be examined to determine practical useful life expectancy. Environment, installation, maintenance, and other service life contributors such as load amount, number of operations, and any traumatic events occurring (major faults, flooding, etc.) all must be analyzed. A comprehensive assessment will help you recognize how close to the end of useful life a piece of equipment may be, and whether it is in your best interest to maintain, replace, or upgrade dated equipment.

Don’t turn a blind eye to your electrical equipment…as you consider longevity, future goals, alterations/expansions, and new equipment efficiency, you should engage a qualified engineer to help with future infrastructure planning and aligning facility goals with funding. When you need expert input for determining any equipment needs, Fitzemeyer & Tocci, Inc. can help determine assess your current situation and recommend the best options available.

Stay tuned for our upcoming guide release on Aligning Infrastructure Decisions with Healthcare Business Plans!


bottom of page