Troubleshooting series: High ambient temperature

It’s the first week of August, and the middle of a heat wave. You — and your equipment — are feeling the heat. Then, at 2:55 pm your phone dings with a new notification: “Motors@Work detects Lift Station #24 Pump 1 at 103°F, nearing max ambient temperature allowed per OEM spec.”

As discussed last week, heat is perhaps the most damaging stress your motor experiences.  Sometimes the motor generates that problematic heat itself; other times, it’s Mother Nature wreaking havoc on your operations.

Here’s how Motors@Work helps you identify, troubleshoot, and resolve motor-damaging high ambient temperature issues that otherwise would have gone undetected without our timely condition-monitoring alerts.

About an hour later your phone dings with a new notification: “Motors@Work detects Lift Station #24 Pump 1 at 109°F, 4°F above max ambient temperature allowed per OEM spec. PROVIDE EXTERNAL COOLING OR DERATE MOTOR & SHED LOAD IMMEDIATELY.”


As discussed last week, motor insulation breaks down at an accelerated rate when the motor’s temperature rises above anywhere from 221°F (105°C) [Class A] to 356°F (180°C) [Class H]. So, why is it a problem to have a motor in a 109°F (42°C) environment?

Most motor enclosures rely on ambient air for cooling. For example, open drip-proof (ODP; IP12 / IP22) motors have vents and an internal fan that circulate ambient air around the motor windings. Meanwhile, totally enclosed fan-cooled motors (TEFC; IC410) use conduction to exhaust heat from the windings, through the laminations, and to the enclosure’s fins; then, air forced over the fins by the external fan and bell-cover provides convective cooling.

However, these motor enclosures were designed to provide sufficient cooling to keep the hottest part of the motor below the maximum temperature for its insulation class — assuming ambient air at or below 105°F (40°C). Hotter — or thinner — air inhibits the motor’s ability to cool itself.

When a motor operates in hotter or thinner (e.g., high altitudes) air, its temperature rises — i.e., heat generated internally due to inefficiencies and magnetic saturation — may exceed the limits for its insulation class. For this reason, NEMA recommends derating, or reducing the effective horsepower, of motors in hot and high-elevation environs per the table below:

Derating factors for high ambient temperatures and altitudes
40°C 45°C 50°C 55°C 60°C
1000 meters 1.00 0.96 0.92 0.87 0.82
1500 meters 0.97 0.93 0.89 0.84 0.80
2000 meters 0.94 0.90 0.86 0.82 0.77
2500 meters 0.90 0.86 0.83 0.78 0.74
3000 meters 0.86 0.83 0.79 0.75 0.71
3500 meters 0.82 0.79 0.75 0.71 0.67
4000 meters 0.77 0.74 0.71 0.67 0.63

You can’t afford to have this motor go down now, so you call your collection system operators and ask them to turn on another pump at this lift station. You work with them to balance the load between the pumps so neither motor carries more than 60% of its rated load. You and the operators decide to keep bringing on pumps as needed to keep each motor’s load well below the derate for the today’s projected high temperature.

Motors@Work’s continuous, near-real-time condition monitoring algorithms watch for these motor-damaging temperatures and send out content-rich alerts that facilitate troubleshooting — so you can keep your motor-driven systems operating reliably.

How will condition monitoring benefit your organization? Email Nicole at to learn more.

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