Switches

Component Related Documentation

A switch is a circuit control element with one or more sets of electrical contacts consisting of a mechanical, electrical or electronic device for making, breaking or changing the connections in an electrical circuit. Each set of contacts can be in one of two states: either “closed” meaning the contacts are touching and electricity can flow between them, or “open,” meaning the contacts are separated and non-conducting. Switches may be manually operated by a human, operated mechanically, by induction or capacitance by a machine member, or by process variables such as pressure, temperature, flow, fluid level, current, voltage, or force, acting as sensors in a process and used to automatically control a system. Large switches may be remotely operated by a motor drive mechanism. Disconnect switches can be used to isolate electric power from a system, providing a visible point of isolation that can be pad-locked if necessary to prevent accidental operation of a machine during maintenance, or to prevent electric shock.

Safety Related Notes

Before working on this machine, perform lockout-tagout procedures per the rules of your plant. Determine the sources of energy on this machine – electrical, pneumatic and hydraulic – and release or vent sources of stored energy – electrical capacitors, air receivers, and hydraulic accumulators. Shut off sources of power – electrical, pneumatic and hydraulic. Safely block mechanical sources of energy such as loaded springs and loaded machine members, or safely position the machine members so they are unloaded and springs are not under tension. Beware of hot hydraulic fluid and hot surfaces which can cause burns. Never “crack a hydraulic or pneumatic fitting” to check for the presence of stored energy. Hydraulic fluid injection injuries, as well as injection injuries from many other fluids, are extremely serious and must be treated immediately by medical personnel familiar with this type of injury. Loss of body parts or death may result from improperly treated fluid injection injuries! Never use your hands to feel for a hydraulic leak! Never use compressed air to blow dust off yourself or someone else – there is risk of an air injection injury. Review the schematics and think before proceeding to work on the machine to ensure you have made the machine safe to work on.