When working on electrical equipment it is critical to ensure that all sources of energy related to the equipment has been controlled. Releasing stored energy in capacitors and short-circuiting any high-capacitance elements is crucial to ensure safety for the worker.

Other sources of energy must also be considered in addition to stored electrical energy. Associated mechanical, hydraulic, pneumatic and similar energy sources are often triggered by the presence of or lack of the associated energized electrical circuit.

In industrial facilities, a circuit being de-energized may result in an automatic shutdown process that involves moving equipment finishing out the current process. Even after the main disconnect for the equipment is shut off, the associated equipment can still be moving until it reaches its final step in the shut down sequence. Ensuring that all sources of energy are immobilized before working on the equipment is a critical step in the lockout/tagout procedure.

Below is a sample of NFPA 70E. For the complete section, see the actual NFPA 70E text at NFPA.ORG. Once there, click on the free access link to NFPA 70E.

120.5(B) Elements of Control. The procedure shall identify elements of control.

(1) De-energizing Equipment (Shutdown). The procedure shall establish the person who performs the switching and where and how to de-energize the load.

(2) Stored Energy. The procedure shall include requirements for releasing stored electric or mechanical energy that might endanger personnel. All capacitors shall be discharged, and high-capacitance elements shall also be short-circuited and grounded before the associated equipment is touched or worked on. Springs shall be released or physical restraint shall be applied when necessary to immobilize mechanical equipment and pneumatic and hydraulic pressure reservoirs. Other sources of stored energy shall be blocked or otherwise relieved to the extent that the circuit cannot be unintentionally energized.

(3) Disconnecting Means. The procedure shall identify how to verify that the circuit is de-energized (open).