Electricity is dangerous.
Seasoned vets in the industry may think they’re experienced enough to cut corners, and new hires might not realize the potential dangers associated with working with electrical equipment.
This is why the National Fire Protection Association (NFPA) has a standard for safe work practices for electrical construction and maintenance. It protects workers, their employers and valuable equipment from health hazards and damage, and reinforces safety as priority number one on the factory floor.
The standard, NFPA 70E, lists six steps that make up the electrical safety process. The primary concern: turn off power before working on electrical equipment! This requires verification and re-verification, which are just two of the steps outlined below.
- Identify Power Sources: Determine all possible sources of power that supply the equipment being worked on. This means digging into the details – check electrical plans, circuit diagrams, panelboard schedules, any identification signs or tags, etc. The equipment may be supplied by multiple power sources, meaning backup generators or interactive power systems (i.e. photovoltaic cells). These must be addressed as well.
- Disconnect Power Sources: Properly interrupt the load current, and then disconnect each power source from the equipment. Interrupting load current can be done with most load break switches, like circuit breakers or safety switches. If the interrupt rating of a circuit breaker is switch isn’t sufficient, more capable means must be used. Fuses can’t be considered a disconnect either, not on their own.
- Verify that Power is Off: Visually verify that all disconnecting means are fully open or in their fully disconnected position. Beyond just switching a breaker, it may be necessary for qualified personnel to open a panel door or cover to make sure there is an air gap between each contact point. If it’s not possible to visually verify disconnect, test the voltage of the circuit using a digital multimeter between all phase conductors, and between each phase conductor and the ground.
- Lockout/Tagout: Apply lockout/tagout devices in accordance with written electrical safety instructions found onsite. Generally, these are locks that keep the disconnecting means open and are equipped with tags that identify the personnel responsible for applying and removing the locks. The identified personnel are the only personnel able to place and remove these locks.
- Verify that Power is Off Again: Once more, use a digital multimeter to test for voltage in the circuit. A multimeter rated Category III is recommended for equipment operating at or up to 480 volts. For smaller, single phase 120-volt circuits, a Category II meter is fine.
- Discharge Stored Electrical Energy: Discharge any capacitors that are used for power factor correction or motor starting. With high voltage equipment, safety grounds must be installed to prevent energized conductors and equipment from inducing hazardous voltage in nearby equipment that’s been de-energized.
When these six steps are appropriately addressed, electrical energy has been removed from all applicable equipment and power cannot appear unexpectedly. Congrats! You’ve satisfied NFPA 70E!