Environmental, Health and Safety Services

Electrically Safe Work Condition

Elimination of potential energy sources is the primary control for electrical hazards, and should be the first consideration when electrical systems are energized at 50 volts or more. An electrically safe work condition (i.e. lockout/tagout) may not be feasible for voltage-testing and diagnostic tasks, in which case administrative controls and appropriate personal protective equipment are required to reduce or minimize the extent of injury in the event of an incident.

It is important to realize, however, that the acts of opening a disconnecting means, measuring for the absence of voltage, visually verifying a physical break in the power conductors, and installing safety grounds all contain some degree of risk because of the potential for an arc-flash event to occur. These acts are all necessary to achieve an electrically safe work condition, and until they are completed, the worker should be wearing personal protective equipment based on the risk assessment conducted. 

Electrically Safe Work Condition

To achieve an electrically safe work condition, requirements of Virginia Tech’s Lockout/Tagout Program must be followed. Personnel performing electrical work must attend EHS Lockout/Tagout Authorized Person training, which addresses hazardous energy sources, general lockout/tagout procedures, when specific written lockout/ tagout procedures are required, and program guidelines.

Special Considerations

Electrical systems and equipment in large facilities rarely stay the same for more than a few months or years. Electrical energy sources are sometimes difficult to identify, especially when the path of circuit conductors is not easily observed or historical work on the system has created questionable standards of practice or compliance. 

Up-to-date drawings should be maintained on electrical systems and equipment and updated as necessary when changes are made. This is often a difficult task, but it is imperative to effectively communicating detailed information to personnel and contractors. Labels are another means of identifying and communicating information, but they must be complete and accurate as well. Inaccuracies identified should be reported to Facilities Electro/Mechanical Services immediately for correction.     

Operating "adequately rated disconnecting means" is the next step in creating an electrically safe work condition. Energy-isolating devices establish a positive break in the conductors supplying energy. Simply operating an on/off control device is not sufficient to disconnect electrical equipment or circuits. The system must then be tested for the absence of voltage. For knife-style disconnects especially, the cover should be opened to visually inspect and verify that all phase conductors have opened.  Poles sometimes fail to open. Sometimes the handle of the energy-isolating device moves, but all the poles remain closed. If the physical break in the power conductors is hidden from view, the worker must assume that an electrically safe work condition has not been established and he/she may therefore be exposed to energized electrical conductors. When exposed to energized electrical conductors, appropriate protective equipment must be used.

voltage testingVoltage testing must be conducted to verify the absence of voltage.  Testing devices are considered safety equipment and must meet the minimum requirements necessary to measure the expected (possible) voltage. Minimum requirements for test instruments, equipment, and their accessories shall include:

  • Appropriately rated for circuits and equipment to which they will be connected,
  • Appropriately designed for the environment to which they will be exposed, and for the manner in which they will be used, and
  • Properly inspected for external defects and damage prior to use each day.

A person’s life frequently depends on the effectiveness of the voltmeter and using it effectively. Therefore, the device should be of high quality, listed or labeled by a Nationally Recognized Testing Laboratory, protected from damage, inspected frequently, and treated with respect. If a cover of electrical equipment has been removed, then the worker is potentially exposed to electrical conductors and circuit parts that are likely energized. When exposed to energized electrical conductors, appropriate protective equipment must be used in conjunction with the test equipment for the hazards involved with the particular task.

It is necessary to verify the integrity of the voltage-testing device. Satisfactory operation on a known source of voltage should be established first. Then the worker should check for the presence of voltage on all conducting components of the equipment to be worked on. Lastly, the testing device should again be verified on a known voltage source. If the device still functions normally and the absence of voltage was verified, the equipment can be considered to be de-energized.

Temporary grounds should be used and properly installed to provide a convenient path for voltage unintentionally generated or flowing through the conductor while it is being worked on under specific conditions.  Grounds should be installed in such a manner as to create a zone of equipotential around the worker to ensure an electrically safe working condition.  The use of temporary grounds has little direct impact on the de-energized condition.  They are intended to drain “unexpected” voltage due to capacitance, transformer action, shorts, or atmospheric static discharge away from the work area. Common examples of when temporary grounds are necessary to work on equipment or systems include:

  • Outside overhead lines, which can be re-energized by any number of sources,
  • Shielded cables installed underground, in a cable tray, or in conduit.

Due to the possibility of large amounts of current flow on the temporary ground, and the need for the ground to remain in place in the event of such current flow, temporary grounds must be constructed per ASTM F 855. Job-made grounds should be avoided due to improper design and materials being used. Temporary grounds must have a fault-duty rating at least equal to the available fault-current capacity at the point in the circuit where it will be installed. Inadequately rated grounds can result in magnetic forces breaking the conductor or connector and whipping it around like a bullwhip.

All grounding clusters that are installed must be removed when the work task is completed. Each one should be assigned a unique identifier, which is recorded when installed. The same record should be reviewed when the grounding cluster is removed.