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EV voltage changes and dangers: What firefighters need to know

Understanding the shift from traditional 12-volt systems to innovative 48-volt architectures, with high-voltage systems becoming the new norm

Modern electric car chassis x-ray vehicle battery in studio environment line art 3d render

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The rapid evolution of electric vehicles (EVs) has brought about significant changes not only in transportation but also emergency response. As the automotive industry transitions from traditional 12-volt systems to innovative 48-volt architectures, and high-voltage systems ranging from 300 to 800 volts become the new standard, understanding these electrical systems is crucial, especially for first responders. Here we’ll investigate the unique characteristics of low- and high-voltage EV systems, shedding light on potential safety concerns and emphasizing the importance of proper training and safety protocols.

EV voltage basics – and what’s changing

EVs are equipped with two distinct electrical systems: a low-voltage system, typically operating at 12 volts, and a high-voltage system. While most of the automotive industry still employs the 12-volt system, Tesla’s Cybertruck has introduced a 48-volt system. This low-voltage system, grounded to the chassis, powers most of the vehicle’s electronics, including crucial safety systems like airbags.


Tesla’s Cybertruck has introduced a 48-volt system.

Photo/Patrick Durham

Many long-standing automotive manufacturers (Ford, GM, VW, etc.) are generally slow to adopt changes in the industry. Assuming a traditional manufacturer decides to embrace this shift, it is unlikely to be implemented in vehicles for another 5 to 7 years. In contrast, Tesla may swiftly adopt this strategy across its entire platform.

Understanding the risks

High-voltage EV battery packs are equipped with isolation relays and fuses designed to automatically disable the high-voltage lines upon detecting an isolation fault or other critical failures, such as an imminent crash or airbag deployment. While these systems typically operate without human intervention, the vehicle is also equipped with fail-safe systems that can be activated by first responders. Always refer to the steps outlined in the emergency response guide to ensure proper disabling of the vehicle.

Emergency Response Guides are vital sources of information, guiding the safe handling of high-voltage circuits, often involving the isolation or deactivation of the high-voltage system. These guides also furnish details about the whereabouts of high-voltage components and wiring, with such wiring being easily recognizable by its distinctive orange insulation and connectors. By adhering to the guidance provided in Emergency Response Guides, responders can effectively navigate high-voltage scenarios with safety and precision.

It should be noted that the distinction between low voltage and high voltage for direct current (DC) is somewhat ambiguous. Different organizations have varying thresholds. OSHA, for instance, deems anything below 50 volts as low voltage, while the Society of Automotive Engineers (SAE) considers anything below 60 volts to fall into this category. In contrast, the International Electrotechnical Commission (IEC) specifies 1,500 volts as the limit for low voltage. Generally, 48 volts would be widely accepted as being low voltage.

The advantage of a 48-volt system lies in the reduction of wire size, primarily due to the decreased current required to power the various devices within the vehicle. Lowering the voltage can lead to more efficient and cost-effective electrical systems, contributing to improved overall performance and reduced energy consumption in EVs.

The shift from a 12-volt to a 48-volt system may prompt concerns among first responders, but overall, it doesn’t pose a significant safety issue. This is primarily because the conductors in a 48-volt system are generally much smaller in size. Moreover, any damage to these smaller wires is likely to trigger fuse blowouts promptly, effectively minimizing the risk of electrical hazards. Given these factors, it would be challenging for first responders to find themselves in a situation where electrocution becomes a serious concern.

The high-voltage system in EVs operates at a range of 300 to 800 volts, with 800 volts becoming typical. This system is entirely isolated from the vehicle chassis and is responsible for powering the vehicle’s propulsion and, in some cases, the HVAC system. The isolation means that components requiring high-voltage power have both negative and positive cables. This setup minimizes the risk of electrocution, as one would need to simultaneously contact both the negative and positive cables.

However, a significant concern with high-voltage systems is the potential for an arc flash. An arc flash is a type of electrical explosion that can occur between two conductors when an electrical current passes through the air between conductors, creating a sudden and intense release of energy. If a tool or a gloved hand is introduced into a compromised set of wires, it can trigger an arc flash. Arc flashes have the potential to cause severe burns due to the extreme heat generated during the flash. Proper precautions and safety measures are crucial when dealing with high-voltage systems to minimize the risk of arc flashes and ensure the safety of responders.

Respect electricity

Any electrical system, especially high-voltage systems in EVs, must be approached with the utmost respect. When responding to incidents involving damaged vehicles, the potential for electrical hazards is present. Firefighters understand that in emergency situations, there are no absolutes, and there is always a risk of injury. Proper training, adherence to safety protocols, and a thorough understanding of the risks associated with EVs are crucial for responders to effectively manage and mitigate potential hazards.

Electric Vehicle Fire Resources

Patrick Durham serves as the captain and training officer at Station 4 within the Troy (Michigan) Fire Department. Durham is a mechanical engineer, presently engaged in cutting-edge automotive industry projects. Notably, he has been involved in designing innovative multi-material battery structures for electric vehicles. Drawing from over 15 years of combined experience as a firefighter and engineer, Durham has developed specialized training courses for firefighters, as well as YouTube content, focusing on various technical aspects, including the specific challenges associated with responding to incidents involving EVs. Durham is also a member of the Technical Panel for Fire Safety of Batteries and Electric Vehicles at UL’s Fire Safety Research Institute, where he contributes his expertise to advance the field of fire safety in the context of emerging battery technologies and electric vehicles. Learn more at StacheD Training or reach Durham via e-mail.