ELECTRICAL SHOCK-SAFE WORKPLACE

• Determine all possible sources of electric supply to the equipment being worked on. – Check electrical plans, one-line diagrams, panelboard schedules, identification signs and tags on electrical equipment, and so on.

• Most electrical equipment has a single source of supply. But sometimes there are multiple sources. Besides this can include emergency and standby generators, interactive power sources such as photovoltaic or fuel cell systems and dual utility feeds for major industrial facilities.

• Sometimes “illegal” circuits are installed that don’t comply with NEC rules. These can create a backfeed hazard after workers have disconnected all the electrical power sources they know about.

• After properly interrupting the load current, open the disconnecting means for each source.

• Most circuit breakers, safety switches, and other disconnecting means are capable of interrupting the load current they carry.

• When the rating of a disconnect is not sufficient to interrupt load current, the load must be removed by another operation before the disconnect is operated.

• Fuses aren’t considered disconnecting means, so a circuit can’t be de-energized merely by removing one or more plug or cartridge fuses. 

• On most premise wiring systems, only the ungrounded (phase) conductors are disconnected. The grounded (neutral) conductors are never intentionally interrupted.

• Attachment plugs of electric appliances such as cooking and laundry equipment are permitted to be used as disconnects.

• Wherever possible, visually verify that all blades of the disconnecting means are fully open, or that drawout-type circuit breakers are racked out to their fully disconnected position.

• Disconnecting means sometimes malfunction, and fail to open all phase conductors when operated. After operating the disconnect’s handle, a qualified person should open the equipment door or cover and look to see that there is a physical opening (air gap) in each blade of the disconnect.

• Lastly, it’s impossible to visually verify the existence of an air gap. In these cases, test for the presence of voltage to verify that the circuit has actually been disconnected. Using a digital multimeter (DMM) or other tester rated for that voltage level, test for voltage between all phase conductors and between each phase conductor and ground (phase-to-phase and phase-to-ground)

• Apply lockout-tagout devices in accordance with the employer’s written electrical safety program. Normally these are padlocks to keep the disconnecting means open, and tags that identify the person(s) responsible for applying and removing the locks.

• Test for the presence of voltage. – Use a digital multimeter (DMM) or other tester rated Category III to test conductors and equipment operating at up to 480 volts.

• Lastly, testers rated Category II can be used on single-phase 120-volt circuits.

• Install safety grounds under certain conditions

• Discharge sources of stored energy such as capacities used for power factor correction and motor starting.

• Lastly, in high-voltage installations such as industrial substations, energized conductors.
• Equipment can induce hazardous voltages in nearby conductors and equipment that are deenergized. On these high-voltage systems, temporary equipment grounding jumpers are installed to establish a safe “equipotential zone” where employees are working.

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