🕒 3 min read •  🟢 Beginner • Educational Resource
The Standard:Â
- ANSI B11 machine safety standards recognize that machines should not automatically restart following a loss and subsequent restoration of power if doing so could expose personnel to hazardous motion.
- Anti-restart protection, sometimes referred to as dropout protection or undervoltage protection, helps ensure a machine requires a deliberate operator action before hazardous motion can resume after an interruption in power.
- This principle is commonly applied to machine shop equipment such as drill presses, mills, lathes, grinders, saws, and similar machinery where an unexpected restart could create a serious hazard.
- Note: Specific requirements vary depending on the applicable ANSI B11 machine-specific standard and machine design. Always consult the standard governing your equipment.
The Practical Translation:
- If the power goes out—even for a fraction of a second—the machine should remain stopped when power returns.
- The operator should be required to intentionally press the Start button or otherwise initiate a new operating cycle before the machine can resume operation.
- Anti-restart protection is especially important during brief power interruptions when an operator may have reached into the machine, adjusted tooling, cleared chips, or assumed the machine was safely stopped.
- While many newer machines include anti-restart functionality, older equipment and modified machines should be evaluated to verify that unexpected restart cannot occur following a power interruption.
- Ask yourself:
- If power is lost while the machine is running, will it remain stopped when power returns?
- Does the operator have to intentionally restart the machine?Â
- Have older machines been evaluated for anti-restart protection?Â
- Have electrical modifications affected the original restart behavior?
The Takeaway:
- Anti-restart protection helps prevent unexpected machine motion following the restoration of power.
- Requiring a deliberate operator action before hazardous motion resumes is an important risk reduction measure for many machine shop machines.
- Compliance identifies the need to prevent unexpected restart. Practical risk reduction asks whether your machine remains safely stopped until someone intentionally commands it to run again.
Want to learn more?
Explore our guide on Anti-Restart (Dropout) Protection for Machine Shop Equipment for practical examples, common retrofit options, and considerations when evaluating legacy equipment.
