Overheating Motors? The Hidden Impact of High Ambient Heat on Electrical Systems

When the Obvious Problem Isn’t the Real Problem

Sometimes when something breaks, it’s not clear where to begin to fix the problem. Worse, sometimes you think you already know the answer, and end up chasing the wrong one.

That’s exactly what happened during a multi-year troubleshooting effort that started with suspected power quality issues and ended somewhere much less obvious.

A seasoned maintenance manager was dealing with recurring overheating and nuisance trips. He had strong instincts and attention to detail, and like many of us, he initially suspected harmonics, switching effects, or even utility-related power quality issues.

What followed was a two-year journey that highlights an important lesson: sometimes the root cause isn’t electrical at all.

The Initial Assumption: Power Quality Issues

In 2023, I visited an industrial facility experiencing overheating fans fed from two motor control centers (MCCs). The system had recently transitioned from across-the-line starters and soft starters to variable frequency drives (VFDs).

Given the changes, our initial concerns were reasonable:

• Harmonics introduced by VFDs
• High-frequency switching impacts on motors
• Utility-side voltage fluctuations during peak demand

We deployed a Megger MPQ power quality meter to capture data and investigate further.

At the same time, issues seemed to appear randomly across the plant, what we half-jokingly called “gremlins in the system.”

Given the complexity of modern electrical systems, many facilities rely on power monitoring and data-driven tools to diagnose issues before they escalate.

A False Start (and a Temporary Fix)

Despite collecting data, the investigation stalled.

• The meter was removed after six weeks
• No formal analysis was completed
• Immediate operational priorities took over

In the meantime, a simple fix was implemented: adding fans to cool the area.

And it worked.

At least temporarily.

Revisiting the Problem Two Years Later

In July 2025, the issue resurfaced.

This time, we approached it more methodically, reinstalling the same power quality meter and running multiple rounds of monitoring.

What the Data Told Us

After several rounds of measurement:

• Voltage sags and swells were minimal
• Rapid voltage changes were infrequent
• Power quality appeared stable overall

We also noticed a small but interesting detail:

• One MCC showed a ~2% voltage increase compared to 2023

This was traced back to replaced conductors and improved terminations, not a problem, but a useful clue.

Still, none of this explained the overheating.

This is where having access to historical and real-time operational data can make a significant difference in troubleshooting.

The Real Root Cause: Ambient Heat

The answer turned out to be much simpler, and easier to overlook.

It was too hot.

What We Found on Site

Temperature measurements revealed:

• Mezzanine areas reaching 105°F
• Nearby concrete walls reaching 125°F

These conditions had a direct impact on electrical systems.

Environmental factors like temperature are often overlooked compared to electrical or control system issues, but they can have just as much impact on system performance.

Impact on Conductors

According to NEC Table 310.15(B)(2)(a):

• At ~104°F, 90°C-rated wire loses ~13% ampacity
• Near 125°F, losses can reach ~24%

That means conductors were effectively undersized for the environment they were operating in.

Impact on Motors

Motors were also operating beyond their intended limits:

• Most standard motors are rated for 40°C (104°F) ambient
• Elevated ambient temperatures reduce allowable temperature rise
• Insulation life decreases significantly under sustained heat

Even upgrading insulation class didn’t fully solve the issue because the ambient conditions exceeded typical design assumptions.

Why the “Simple Fix” Worked

Adding fans helped reduce ambient temperatures just enough to:

• Lower conductor stress
• Extend insulation life
• Reduce overheating events

But this was only a short-term solution.

It treated the symptom, not the root cause.

Long-Term Solutions for High Ambient Heat

Addressing high ambient temperature requires a more deliberate approach.

1. Reduce Ambient Temperature

• Improve ventilation or HVAC
• Isolate heat-generating processes
• Rethink equipment layout where possible

2. Design for High-Temperature Environments

• Account for ampacity derating in conductor sizing
• Evaluate conduit and tray placement (especially overhead)
• Avoid routing near major heat sources when possible

3. Evaluate Equipment Ratings

• Consider motors designed for high ambient environments
• Verify insulation ratings and expected temperature rise

Be aware: designing for high ambient conditions can increase costs and create physical constraints (such as larger conductors that are difficult to terminate).

A Practical Lesson for Engineers and Plant Teams

This experience changed how I walk through facilities.

Now, I look for:

• Heat buildup near ceilings and mezzanines
• Conduit and cable trays installed in hot zones
• Electrical systems located near process heat sources

It’s easy to focus on complex electrical explanations, but environmental factors like heat can have just as much impact, if not more.

Final Thoughts

The more time you spend troubleshooting, the more you realize how often problems hide in plain sight.

If your facility is experiencing:

• Intermittent overheating
• Nuisance trips
• Unexplained equipment failures

It may be worth stepping back and asking a simple question:

Is the environment part of the problem?

If you’re seeing similar issues, our team can help evaluate how power quality, ambient heat, and aging infrastructure may be impacting your system reliability—and help you identify practical solutions.

You are not just selecting a price.
You are selecting the likelihood of success.

Choosing the right partner can have a lasting impact on your project’s cost, schedule, and overall performance.

If you are evaluating engineering or system integration partners, explore how Hallam-ICS supports complex projects with a focus on execution, risk reduction, and long-term value.

Frequently Asked Questions About Ambient Heat and Electrical Systems

How does high ambient temperature affect electrical systems?

High ambient temperatures reduce the ampacity of conductors and increase thermal stress on equipment. This can lead to overheating, insulation degradation, and premature equipment failure.

Can ambient heat cause motor overheating even if power quality is good?

Yes. Even with stable voltage and minimal harmonics, excessive ambient heat can push motors beyond their rated operating conditions, reducing lifespan and causing overheating.

What temperature is too high for electrical equipment?

Most standard electrical equipment and motors are rated for 40°C (104°F) ambient. Temperatures above this require derating or specialized equipment.

How do you mitigate high ambient temperature in industrial facilities?

Common solutions include:

• Improving ventilation or HVAC
• Relocating equipment away from heat sources
• Upsizing conductors for derating
• Using high-temperature-rated equipment

Why is ambient heat often overlooked in troubleshooting?

Because many issues initially appear electrical (trips, faults, overheating), teams often focus on power quality or controls before considering environmental conditions.