High-Voltage EV Maintenance Safety

1. Understanding the Risks: Why High Voltage is Lethal

The high-voltage (HV) systems in new energy vehicles (NEVs) typically operate between 300V and 600V, with some 800V architectures exceeding 800V. In contrast, the human body's safe voltage limit is merely 36V. This means an EV's electrical architecture operates at dozens of times above the safe threshold for human exposure.

HV electrical hazards mainly manifest in two ways: electric shocks (current flowing through the body causing internal trauma) and arc flashes (severe burns resulting from high-temperature electrical arcing). In 2025, an accidental mishandling by technicians on a Deepal NEV at a service centre caused a high-voltage short circuit in the traction battery pack, sparking an immediate fire. In another incident, a technician attempted to remove a battery pack without isolating the power supply; he sustained an electric shock the moment he touched the wiring harness and collapsed instantly. These incidents serve as a stark reminder: HV safety protocols are strictly non-negotiable.

2. Regulatory Framework and Safety Standards

HV servicing safety is governed by several mandatory national standards:

• GB/T 44510-2024 "Technical Requirements for Maintenance and Servicing of New Energy Vehicles" : In effect since 1 January 2025, this standard outlines fundamental servicing criteria, workshop safety protocols, and routine maintenance checklists for NEVs.

• GB 18384-2025 "Electric Vehicles Safety Requirements" : Taking effect on 1 July 2026, this mandates that all vehicles must be fitted with a high-voltage or low-voltage manual service disconnect (MSD) and standardises service inspection safety workflows. The HV disconnect unit must meet IPXXB ingress protection, or ensure live components drop below safe voltage levels within 1 second of de-energisation.

• GB 38031-2025 "Electric Vehicles Traction Battery Safety Requirements" : Enforced concurrently, this elevates thermal runaway mitigation standards to a strict "no fire, no explosion" benchmark.

Regional authorities are also rolling out localised guidelines. For instance, the Beijing Municipal Safety Management Code for NEV Maintenance (Draft for Comments) establishes comprehensive requirements covering workshop governance, safety SOPs, and emergency countermeasures.

3. Technician Qualification Requirements

Technicians handling NEV high-voltage systems must fulfill the following prerequisites:

• Hold a valid Low-Voltage Electrician Special Operation Certificate

• Complete and pass certified EV technical training

• Deploy at least two certified HV technicians on-site for any live electrical or HV service work

• Operate under a service centre that holds official accreditation and business filing

Manufacturers such as Tesla strictly stipulate that only technicians who have completed all mandatory HV certification courses are authorised to carry out HV repair procedures.

4. Standard De-Energisation and Voltage Verification Workflow

Prior to any work on HV components, technicians must rigorously execute the following procedure:

Step 1: Safe Parking and Power Isolation
Ensure the car is safely parked, shift into Park (P), and engage the parking brake. Switch the ignition to OFF and wait for roughly 5 minutes. Disconnect the negative terminal of the 12V auxiliary battery and wait for at least 15 minutes to guarantee full system de-energisation.

Step 2: Disconnect the Manual Service Disconnect (MSD)
Most EVs feature a Manual Service Disconnect (typically a bright orange high-voltage plug situated near the battery pack or beneath the rear bench). Always wear insulated gloves and use insulated tools when pulling the MSD. For vehicles without a dedicated MSD, disconnect the traction battery's main high-voltage busbar harness connector.

Step 3: Allow Capacitor Discharge
High-voltage circuits can retain residual electrical energy even after shutdown. Technicians must allow the manufacturer-specified discharge period—typically 5 to 15 minutes, or longer for certain models. Waiting for capacitor discharge is a compulsory safety requirement, not an option.

Step 4: Voltage Verification (Zero-Potential Check)— The most critical step:

• Use a certified multimeter to test between exposed conductive components and the chassis ground; the reading must be below 5V

• Measure across the positive and negative terminals of the HV cabling; the reading must also be below 5V

• Confirm that the voltage across the traction battery's main HV outputs is below 36V and insulation resistance tests pass before starting any mechanical work

5. Personal Protective Equipment (PPE)

Appropriate certified PPE must be worn at all times during HV maintenance operations:

Crucial Reminder: When working on HV cables, busbars, or connectors, dielectric gloves must remain on throughout. Before starting, remove all metallic jewellery (watches, rings, chains, etc.) and clear all loose metal items from pockets.

6. Insulated Tooling Standards

Using conventional metal hand tools around HV electricals poses severe arc-flash risks. Technicians must use VDE-certified 1,000V insulated hand tools, including insulated spanners, screwdrivers, socket sets, and pliers. All HV diagnostic equipment requires routine calibration, with insulation multimeters undergoing periodic recalibration checks.

Additionally, the service bay must be equipped with:

• Insulation Tester (Megohmmeter) : For measuring insulation resistance between the HV system and vehicle chassis

• Lockout/Tagout (LOTO) Kit : To prevent accidental power reconnection during service

• Thermal Imaging Camera: To quickly identify abnormal hotspots and thermal anomalies

7. Workshop Environment and Operating Protocols

• Dedicated Bay Setup: Work must be carried out in a dry, well-ventilated dedicated bay, cordoned off with safety barriers and clearly marked with "High Voltage Danger" warning signs

• Buddy System: HV operations require a minimum of two qualified technicians working in tandem, strictly adhering to high-voltage electrical safety standards

• Static Discharge: Discharge residual body static before touching any electronic modules

• No Live Maintenance: Never service or dismantle HV components while the vehicle is plugged in and charging

• No Metal Accessories: Metallic accessories are strictly forbidden in the work bay

• Terminal Insulation: Immediately fit insulating caps or covers over exposed live terminals once connectors are unplugged

8. Emergency Response Procedures

Electric Shock First Aid:

1. Isolate the main power source immediately; never grab the victim with bare hands

2. Use an insulated rescue hook or non-conductive rod to pull the casualty clear of live parts

3. Administer cardiopulmonary resuscitation (CPR) immediately if required and call emergency medical services (999/112)

Battery Thermal Runaway (Smoke, Fire) :

• Deploy specialist fire suppression equipment (such as copious water mist or dedicated lithium-battery fire extinguishers)

• Do not use standard ABC dry powder extinguishers directly on an open battery fire

Submerged or Crash-Damaged Vehicles:

• If an EV is flood-submerged, the HV circuitry is vulnerable to short-circuiting. Power down the ignition switch and evacuate the perimeter immediately

• For rescue extrications requiring structural cutting, isolate the HV power first and wait at least 10 minutes, ensuring all cut points steer clear of orange high-voltage harnesses and components 

9. The Cardinal "Ten Rules" of HV Servicing

Always adhere to these fundamental principles when working on NEV high-voltage systems:

• Do not touch live HV components, do not measure battery terminal voltage without protocols, and do not dismantle the battery pack without authorisation—The "Three No's" rule

• Never work wearing metallic jewellery or accessories

• Never work on HV systems alone

• Never skip the voltage verification process

• Never use standard, non-insulated tools

• Never perform repairs while the car is charging

• Never assume "switched off" means safe—always verify with a multimeter

Conclusion

High-voltage safety is the most critical discipline in modern EV aftersales and servicing. From technician accreditation, standardised de-energisation workflows, and PPE compliance to certified insulated tooling and emergency drills, every single step is a matter of life and death. The new safety standards coming into force in July 2026 place even stricter hardware-level mandates on service disconnect mechanisms. For EV technicians, "isolate before you touch, and verify before you work" is not just a workshop slogan—it is the ultimate golden rule of survival.