High Voltage Electrical Safety Explained

High Voltage Electrical Safety
Working on high voltage systems — systems greater than 600 volts — must be performed using de-energized electrical safety work practices, whenever possible.

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Only qualified electrical workers can work on power systems greater than 600 volts, and in these situations, the following requirements and work practices are required for energized electrical work:

• Work on greater than 600 volts must include the use of permits, knowledgeable qualified high voltage electrical workers, appropriate tools, Personal Protective Equipment (PPE), and safety observers.
• The operating voltage of equipment and conductors must be determined before performing any energized electrical work. This should be performed using a high voltage probe designed for high voltage circuits at the level of voltage to be encountered.
• Know the clearance requirements for high voltage equipment, barrier and barricading requirements;
• Understand special hazards associated with high voltage equipment;
• Understand special procedures and tools for extracting personnel from energized circuits and providing rescue and resuscitation, and;
• Understand the workspace and guarding specified in the OSHA standard.

In addition, all qualified high voltage workers should have the skills necessary to distinguish exposed live parts from other parts of electrical equipment, and to determine the nominal voltage of exposed live parts. Although the National Electrical Code (NEC) considers anything over 600 volts to be high voltage, voltages of more than 50 V can cause heart fibrillation if applied across dry unbroken human skin. If the skin is wet or penetrated by electrodes, voltages as low as 40 or even lower can be lethal.

Voltages above 1,000 V have special clinical characteristics as far as burn wounds, whereas below that level, cardiac fibrillation is the major risk. Voltages above 1,000 V also present the risk of wounds leading to amputation.

Workers trained in “live line” techniques – working on high-voltage and extra-high-voltage transmission lines, are allowed to use “hands on” contact with energized equipment. In this situation, the trained qualified personnel — although electrically connected to the high-voltage line — is insulated from the earth so that he/she is at the same electrical potential as the line.

Despite this, live-line workers often use protective equipment and clothing while working in high-voltage situations to ensure their safety. This type of equipment prevents the formation of an unwanted arc. High voltage circuit breakers use a blast of air or SF6 dielectric gas or immersion in mineral oil when the HV circuit is broken.

Regulations you need to know about working with high voltage current are:

• NFPA 70 E – Standard for Electrical Safety in the Workplace
• 29 CFR 1910.137 – Electrical Protective Devices
• 29 CFR 1910 Subpart S – Electrical
• 29 CFR 1910.147 – The Control of Hazardous Energy (Lockout/Tagout)
• 29 CFR 1910.269 - Electric Power Generation, Transmission, and Distribution
• ANSI C2, the National Electrical Safety Code

Although the regulations and standards are drawn from American sources, the same guidelines can be applied for Canadian workers.