Why Wrench Time Studies Are Outdated: A Modern Maintenance Perspective

For a long time I believed the “wrench time” concept had fallen out of use. Yet over the past year I’ve partnered with two organizations that still rely on it, and the topic keeps resurfacing in conferences and publications. I suspect consultants and academics are the main drivers of its persistence. If you’re on the shop floor, I’d love to hear your thoughts—comment at the end of this post.

What Exactly Is Wrench Time?

Wrench time emerged in the early 20th century as an extension of time‑and‑motion studies originally developed for assembly line workers. For maintenance technicians, it measures the percentage of an employee’s shift spent actively using tools—excluding travel, planning, parts retrieval, thinking, or any non‑wrench activity. A typical study reveals that craftspeople spend only 25‑35% of their time actually working with a tool.

Why Wrench Time Studies Often Mislead Management

• It Upsets the Workforce: Communicating that technicians aren’t “working hard enough” can demoralize the team. Even if the intent is to spot planning or storage issues, the initial shock can drive people to over‑report wrench time in subsequent studies.
• It Obscures Root Causes: If the goal is to improve planning, scheduling, or materials flow, addressing those systems directly yields clearer results than a wrench‑time metric that masks underlying problems.
• It Skews Performance Perception: Using an average figure treats slackers and top performers alike, making the best technicians look poor while normalizing mediocre work. Leaders should celebrate high performers, not penalize them.
• It Ignores Modern Maintenance Roles: Skilled technicians often spend 20‑30% of their time in critical thinking, root‑cause analysis, CMMS data entry, and collaborative design reviews. Wrench time gives a zero for these essential activities, undervaluing the true value added.
• It Measures the Wrong Outcome: Maintenance departments deliver equipment reliability, not just service hours. While a high wrench‑time ratio may be appropriate during planned shutdowns, for routine operations it can be misleading.
• It Ignores Job Duration: If a task takes longer than necessary, the wrench‑time percentage rises—further obscuring inefficiency. Employees should be busy with the right tasks, not just busy.

I understand that many maintenance leaders still see value in wrench‑time studies. The debate continues: Should we abandon the concept entirely, or can it be adapted for today’s high‑performance plants? Share your perspective below.

About the Author
Torbjörn (Tor) Idhammar is Partner and Vice President of IDCON Inc., a leading firm in reliability and maintenance management. He oversees all projects and consultants, offering training and implementation support across reliability assessment, preventive maintenance, operator‑based reliability, planning and scheduling, materials management, and root‑cause problem elimination. Tor is the author of Condition Monitoring Standards (Volumes 1‑3).
Contact Tor at 800‑849‑2041 or email info@idcon.com. Visit www.idcon.com.