When a VFD faults or a hydraulic hose bursts for the third time in a month, your team has two options: replace the part again or find out why it keeps happening.
Root cause analysis (RCA) is what separates plants that improve from plants that stay stuck in the same break-fix cycle. For context on how RCA fits into the broader diagnostic process, start with our industrial equipment troubleshoot guide.
What Is Root Cause Analysis for Equipment Failures
Root cause analysis is a structured problem-solving method to find the core reason behind an industrial equipment breakdown.
It goes past the immediate physical cause to find the systemic, latent, or human cause. A bearing fails because of friction. That’s the symptom. The root cause might be that the lubrication schedule in the CMMS was set incorrectly, which is an organizational failure, not a mechanical one.
RCA turns a break-fix team into a continuous improvement team.
The 5 Whys Technique
The simplest RCA tool is the 5 Whys. Ask “Why?” five times and you peel back the layers of a failure.
- Why did the machine stop? The motor tripped the overload.
- Why did it trip? The motor drew too much current.
- Why did it draw too much current? The bearings seized.
- Why did the bearings seize? Washdown water contaminated them.
- Why did water get in? The wrong seal type was specified for this environment.
That last answer is the root cause. Fix the seal specification, and the bearing won’t fail again.
Any tech on your floor can use this tool. It doesn’t require special software or engineering expertise.
The Fishbone (Ishikawa) Diagram
For complex failures across multiple systems, a Fishbone diagram organizes potential causes into categories:
- Man: Was the tech trained properly?
- Method: Was the PM procedure correct?
- Machine: Is the asset near the end of its life?
- Material: Was the replacement part a quality OEM component?
- Environment: Is the plant too hot or humid for the electronics?
This visual approach helps teams see connections between causes that aren’t obvious when you look at each factor alone. For failures that involve both mechanical and control system elements, see our guide on troubleshooting industrial control systems for the hardware and software context.
Data-Driven RCA
RCA without data is just guessing with extra steps.
Your team needs to pull fault logs from the PLC or VFD, review the asset’s maintenance history in the CMMS, and check oil analysis results for wear particles in hydraulic fluid or gearbox oil. That data tells you whether the failure was a one-time event or part of a pattern.
For common patterns in mechanical failures that data often reveals, see our guide on mechanical failures in industrial equipment.
RCA vs Troubleshoot
These are two different activities. Techs confuse them constantly.
Troubleshoot gets the machine running. RCA runs after the machine is running, to make sure it doesn’t fail again. Both are important. Neither replaces the other.
For the structured six-step process that gets the machine running first, see our guide on the industrial equipment troubleshooting process.
Recommended ITC Learning Courses
- Troubleshooting Skills: Covers logical thinking and structured problem-solving practices that directly support RCA methodology.
- Statistical Process Control: Teaches data analysis tools, including control charts and problem-solving techniques for identifying failure patterns.
Key Takeaways
- RCA identifies why the failure happened, not just what failed.
- The 5 Whys is a simple tool any tech can use on the floor.
- Fishbone diagrams help visualize complex failures across multiple systems.
- Stop repeating failures, and OEE improves directly.
- RCA runs after troubleshooting gets the machine back up, not instead of it.
Want your team to stop fixing the same failures every month? Contact ITC Learning to explore reliability and RCA-focused training for your maintenance crew.
Frequently Asked Questions
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When should you run an RCA?
You should run an RCA for any failure that causes more than 4 hours of downtime or involves a high-cost component. For recurring failures on the same asset, run one every time.
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Is RCA different from troubleshooting?
Yes. Troubleshoot finds the fault and gets the machine running. RCA is the investigation after the machine runs to find out why it failed and prevent it from happening again.
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How do you get techs to use RCA?
Add a "Root Cause" field to your CMMS work orders and provide training on the 5 Whys. When it's part of the standard work order process, techs use it automatically.
