Manufacturers use a variety of strategies to prevent machines from starting up unexpectedly during maintenance. One of these strategies is to use an enable switch. This is a three-position (OFF-ON-OFF) switch that allows a machine to operate only when the switch is lightly pressed and held in the middle position.
What are the advantages of an enable switch?
When personnel must enter a hazardous area to perform work (such as troubleshooting, setup, programming or servicing of automated machinery) while allowing safe motion, an enable switch can offer the requisite margin of safety when other safeguarding means are impossible or impractical. This gives the operator more control of the motion inside the hazardous area.
Typical activities for which an enable switch can be used include visual observations, minor adjustments, troubleshooting, calibration, tool changes, and lubrication. A risk assessment must be performed to determine the level of reduced performance.
One disadvantage of enable switches is that they only protect the operator, so when more than one person is inside the safeguarded area, multiple devices must be supplied. Additionally, ergonomic issues could result from sustained activation.
What’s the proper way to use an enable switch?
Before accessing the machine, the operator typically needs to place the machine in a reduced performance role, such as a maintenance or adjusting stage. In the event of an unexpected event, this ensures that the operator will either release or squeeze the actuator of the enabling device and disable the machine before a potential injury occurs.
If the enabling device is released or compressed past the midpoint, a stop command is sent to the machine, and the cycle must be reset. Tests have shown that human reaction to an emergency may be to either release an object or hold onto it more tightly. Design and installation of the enabling device should consider the ergonomic issues of sustained activation.
According to ANSI B11.0-2015 - 220.127.116.11, which discusses removing, disabling, bypassing or suspending safeguards, alternative risk reduction measures must be provided when tasks such as startup, setup, repair, adjustment or maintenance require removing, disabling, bypassing or suspending one or more safeguards.
Interested in learning more about this machine safeguarding option? Take a look at our A4EG grip-style enabling switch!