Just because you’ve got a backup or spare electric motor doesn’t mean it’s ready to go into service or that it will even work. And we’ve seen that happen to our customers, time and time again–and it’s especially problematic when it’s a critical motor that’s gone down. So, let’s talk about what happens to spare motors that make them unreliable and what you can do to prevent it.

What Can Happen to Spare Motors

When an electric motor fails, having a spare on site won’t help reduce expensive downtime and productivity loss unless it is ready to run. And several things can happen to a spare motor in storage, even when stored indoors.

For example, long-term storage of a electric motor in a humid environment will eventually lead to rusted bearings and rust flakes. Those rust flakes can fall into the bearing lubrication, causing the bearings to wear out prematurely and making motor failure imminent. And rust also increases friction, which further accelerates bearing and shaft wear.

That’s not all. The motor’s electrical insulation can absorb excess moisture that leads to motor winding failure. And this issue isn’t limited to motors stored outdoors. In some climates, it can be extremely difficult to control humidity levels within a facility of any size.

For motors stored outdoors, there can be problems with insects, rodents, and other small animals that choose to take up residence in spare motors. Such unwanted inhabitants can leave behind contamination and cause severe and expensive damage to the motor windings.

Even indoors, spare motors can be exposed to dust and debris if not covered correctly. Your facility may be climate controlled, but it may not be the right conditions for storing spares. Electric motors must be kept above the dew point or moisture can collect inside them. And don’t forget that rodents can be a nightmare both outside and inside your facility.

Vibration from nearby traffic, machinery, and even forklifts running nearby will affect electric motors. Over time, vibration causes the bearings to experience false brinelling. When false brinelling occurs, indentations within the bearing or shaft develop. These indentations increase friction, accelerate wear, and lead to unexpected motor failure.

Motor shafts that aren’t partially rotated regularly will lead to a sagging rotor and misalignments. These issues cause accelerated bearing wear, vibrations, and an uneven air gap.

If you store your motors on-site, they can accidentally be damaged by other equipment such as forklifts or other material handlers.

Long Term Storage for Spare Electric Motors

You can’t depend on your spare motors if they aren’t stored properly. There are specific recommendations for motors to be stored long term (i.e., six months or more), including

  • Relative humidity no more than 60%
  • Shock or vibration levels that are less than 0.15 in/sec
  • Consistent ambient temperature (50°F and 120°F works best)
  • If there is a chance of ambient temperature reaching the dew point, space heaters should be used

Maintenance and Testing for Spares

Here are some of the maintenance tasks that need to be performed before a spare motor goes into storage …

  • Grease anti-friction bearings
  • Coat all external surfaces of the motor with a rust preventative
  • Ensure that the environment is clean to prevent contamination exposure
  • Perform insulation resistance to ground (Megger and/or polarization index) test

Once in storage,

  • Purge and replaced old grease at least every three years
  • Rotate motor shafts 1 ¼ turns at least every three months, documenting the direction and amount of rotation
  • Perform insulation resistance to ground test at least twice a year
  • Test winding insulation every 30 days

Spare Motor Management and Documentation

Spare electric motors without documentation are risky. For example, when was the shaft last rotated? When was a Megger test performed, and how does it compare to previous tests? These questions and more come up when ensuring that a spare is ready to use. Here are some examples of what type of information should be documented for your motors:

  • Manufacture, model number, data of purchase, etc.
  • Location
  • Record of repair history and reports
  • Results of Megger testing
  • When the shaft was last rotated, its direction, and the amount of rotation
  • Usage data

Effective motor management organizes the data for your spares, makes it easy to access, and simplifies the process of recording the data.


Keeping spare motors onsite for critical assets is a great idea, but these motors need to be maintained, too. Spare motors are often an afterthought until one of the primary motors goes down. If they haven’t been regularly checked and maintained, there’s a strong possibility that your spares won’t work.

Hi-Speed Industrial Service offers a full range of services to help you feel confident about the reliability of your spare motors. We have an incredible team of experienced technicians that will perform all the necessary testing and maintenance for your spares, before and after they go into storage. Hi-Speed can also help motor management for your spares, as well.

We can also assist you in finding a suitable environment for storing your motors and advise on the steps you need to take (e.g., rodent control, vibration dampening, dessicants) to ensure your motors remain reliable.

To learn more, contact Hi-Speed today!