1. High-Voltage Hazards and Safety

LO 6-03: Identify and describe the safety hazards associated with high-voltage chassis systems and outline control practices.

 

High-Voltage Hazards and Safety

In the automotive industry, high-voltage hazards refer to current levels above 60 volts direct current (VDC) and 30 volts alternating current (VAC). These are considered minimum thresholds for risk of significant personal injury or even death from electrical energy. High-amperage shorts can produce blinding lights, fires, and explosions; current levels do not need to be high to cause severe injuries. Reactions to even a light shock can have serious consequences because a technician may jump or fall in response to the current TABLE 6-1. On running diesel engines, high-voltage hazards are encountered when in contact or when testing some injector circuits. Unit injectors typically open control valves at 100 volts (DC) while common rail injectors will operate up to 250 volts (DC) Figure 16.

 

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FIGURE 06-16: The injectors on many diesel engines operate at above 100 volts (DC).

 

  TABLE 06-1: Effects of Various Levels of Alternating and Direct Current  
Effect of Current AC DC
Sensation 1 milliamp at 60 Hertz (Hz) 5 milliamps
Muscle contraction 60 milliamps at 60 Hz 300–500 milliamps
Let-go limit 10.5 milliamps 15–88 milliamps
Minimum hazard threshold with worst circumstance (i.e., standing in water) 60 volts peak AC 42 volts
Nonlethal limit under common working conditions 60–150 volts 60–150 volts

 

Electric vehicles using stored energy are high-voltage hazards capable of delivering a fatal electric shock. Shock hazards commonly include:

  • Components and cables with stored high voltage that contain dangerous electrical current even after a vehicle is switched off
  • Storage of electrical energy with the potential to arc and short to ground, causing explosions or fires
  • The potential for fires and explosions from the release of gases and harmful liquids from damaged or overcharged batteries
  • Permanent magnet electric motors that may allow the vehicle to move unexpectedly due to magnetic forces within the motor
  • Handling risks associated with battery replacement

Given that battery voltages of up to 850–1000 volts are found on commercial vehicles, technicians must develop a wider knowledge base and skill set related to electrical vehicle repair. Adequate product and safety training, as well as access to specialized tools, equipment, and service information, is mandatory to be able to work safely. To help identify high-voltage cables, a bright-colored orange shielding is wrapped around them, and they also have bright-orange insulation Figure 17.

Because of the increased risk associated with higher voltage, most jurisdictions have established health and safety or occupational safety standards mandating that technicians working directly on high-voltage systems have documented qualifications associated with performing electrical work. This means that before working on high-voltage systems and components, technicians must complete related service training in an approved manner, which is usually done by a manufacturer.

The length and content of electrical service training depends on the brand, model, and type of electric vehicle as well as on the technician’s responsibilities. Whether the technician is repairing, servicing, salvaging, or fixing accident damage can dictate the type of training qualifications. In the U.S., OSHA requires workplaces performing service and repairs to have an effective LOTO program in place to protect workers from unexpected start-up or release of stored electrical energy that can lead to serious injury or even death.

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FIGURE 06-17: Bright-orange insulation over electrical cables is used to help identify high-voltage hazards on electric vehicles.

 

When working on a high-voltage battery storage system, there are numerous hazards, such as electrical current, explosions, and chemical burns Figure 18. Two people are required in case one person is harmed or becomes incapable of removing themselves from a live electrical circuit. Scaffolding is a must when working around or servicing overhead battery systems Figure 19. In addition, nonconductive body hooks and Class D fire extinguishers are required at scaffolding level.

  Fig06_18

FIGURE 06-18: Warning labels on batteries used in electric drive commercial vehicles.

   Fig06_19

FIGURE 06-19: Purpose-made scaffolding is required when working on rooftop battery tubs used by hybrid and other electric vehicles.

  

 

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