A comprehensive guide to the regulation governing the safety of battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and their high-voltage systems — covering electric shock protection, battery abuse testing, thermal propagation, charging safety, and post-crash requirements.
Revision 3 (2021)Part I + Part II60+ CountriesBEV · HEV · REESS
What is UN Regulation No. 100?
UN R100 is the internationally harmonised safety regulation for Battery Electric Vehicles (BEVs), Hybrid Electric Vehicles (HEVs), and their high-voltage (HV) electrical systems. Published under the UNECE 1958 Agreement, it is legally binding in all signatory countries including every EU member state, the UK, Japan, South Korea, and Australia.
The regulation addresses the specific hazards introduced by high-voltage propulsion systems that have no equivalent in conventional internal combustion engine vehicles:
⚡ Electric Shock
Direct & indirect contact with HV systems during operation, charging, and after a crash
🔥 Thermal Runaway
Uncontrolled exothermic reaction in battery cells spreading to adjacent cells and pack
💥 Fire & Explosion
Battery fire from abuse conditions including overcharge, external short circuit, and mechanical crush
🏥 First Responder Safety
Protecting emergency services from electrocution during accident rescue operations
Core mandate: Protect occupants, first responders, and bystanders from HV electrical hazards during normal use, crash events, and charging.
History & Evolution of UN R100
UN R100 was first adopted in 2002 as ECE R100, initially focused on preventing electric shock from HV systems during vehicle operation. It has been revised progressively as the EV market grew and new failure modes — particularly battery fires — emerged.
2002
First adopted
2010
Rev. 1 – HV scope
2013
Rev. 2 – REESS Part II
2018
Amend. 1 – charging
2021
Rev. 3 – thermal prop.
Originally focused on protection against electric shock from HV systems during vehicle operation
Revision 2 (2013) added standalone REESS (battery pack) requirements as Part II — enabling independent component approval
Revision 3 (2021) introduced mandatory thermal propagation testing for the first time globally — the most significant update driven by widespread EV fire incidents
Structure: Part I and Part II
UN R100 is divided into two distinct parts that can be applied independently or together:
PART I — Vehicle Safety
Protection against electric shock (direct & indirect contact)
HV bus isolation resistance monitoring (IMD)
HV system capacitor discharge after crash
Connector & coupling protection (IP rating)
Protection during charging (AC & DC)
Vehicle functional safety requirements for HV
Applies to M, N, L category vehicles with REESS > 60V DC or 25V AC
PART II — REESS Safety
Vibration endurance (sinusoidal & random profiles)
Thermal cycling and temperature shock tests
Mechanical shock and crush protection
Fire resistance (external fire exposure test)
Short circuit protection (external)
Overcharge & over-discharge protection
Thermal propagation — no catastrophic event for ≥5 min after single-cell failure
Scope & Vehicle Categories
Category
Description
Examples
M1
Passenger cars — ≤ 8 seats + driver; full Part I & II apply
Cars, SUVs, electric passenger vehicles
M2/M3
Minibuses & coaches — electric buses increasingly common in urban fleets
Electric city buses, coaches
N1
Light commercial vans — GVM ≤ 3.5 tonnes
eSprinter, e-Transit, Kangoo Z.E.
N2/N3
Heavy trucks (> 3.5 t) — electric HGVs and semi-trucks now entering R100 scope
Electric semi-trucks, HGVs
L
Motorcycles, mopeds, quadricycles — lighter voltage thresholds apply
Electric motorcycles, e-bikes (L3)
REESS only
Part II can apply to a REESS independently certified for fitment across multiple vehicle types
Standalone battery pack certification
HV threshold: > 60V DC or > 25V AC. Systems below these limits are exempt from R100 HV provisions.
Electric Shock Protection — Part I
Part I of R100 defines four layers of protection against electric shock:
1
Direct Contact Protection
All live HV parts must be physically inaccessible — IP rating of at least IPXXB (finger probe) for all accessible surfaces. HV connectors must be shrouded.
IMD continuously measures isolation resistance between HV bus and vehicle chassis. Minimum: 100 Ω/V for DC, 500 Ω/V for AC. Driver warning triggered if threshold is breached.
3
Post-Crash HV Discharge
Capacitors on the HV bus must be discharged below 60V DC within 5 seconds of a crash trigger. This protects first responders cutting into the vehicle from electrocution.
4
Potential Equalisation
All exposed conductive parts of HV components must be bonded to the vehicle chassis. Resistance must be < 0.1 Ω between any two exposed metal parts.
Charging Safety Requirements — Part I
AC
Mode 2 / Mode 3 conductive charging
DC
CCS / CHAdeMO rapid charging
WPT
Wireless inductive charging (R100 + R10)
During charging the vehicle HV system is directly connected to external supply — the highest-risk period for electric shock
R100 requires that hazardous live parts are inaccessible during the entire charging sequence (before, during, and after plug insertion)
Automatic disconnection of the HV bus from the charger inlet if the vehicle moves during AC charging (interlock mechanism)
Shock protection must be maintained even if the charging cable is removed whilst HV is still present
Ground continuity must be verified before HV is connected — a broken PE conductor must prevent charging from starting
For DC rapid charging: isolation monitoring must be active; maximum touch voltage on the connector housing ≤ 1V peak
Charging status must be clearly indicated to the driver via a visible or audible signal
REESS — Rechargeable Electrical Energy Storage System
The REESS is the complete battery system as fitted on the vehicle — it includes cells, modules, the BMS, casing, cooling system, and HV connectors. Part II of R100 sets standalone safety requirements for the REESS, tested as a complete unit independent of the full vehicle.
Allows REESS suppliers to obtain their own type approval — OEMs can then deploy pre-approved packs across multiple vehicle models without re-testing
Covers all REESS chemistries: lithium-ion (NMC, LFP, NCA), solid-state (emerging), and others
The BMS is the core safety element — it must enforce overcharge, over-discharge, over-temperature, and over-current protection
Part II abuse tests assess whether the REESS can survive extreme conditions without endangering occupants
✓ No Fire
✓ No Explosion
✓ No Toxic Gas Hazard to Occupants
Part II — REESS Test Requirements
Part II defines eight abuse tests to which the REESS must be subjected and pass without catastrophic failure:
Vibration
Sinusoidal sweep 7–50 Hz and random vibration per IEC 62660-2; simulates road vibration over vehicle lifetime
Thermal Cycling
Temperature cycling −40°C to +85°C; minimum 5 cycles; checks for seal degradation and internal stress cracking
Mechanical Shock
Half-sine shock 25 g / 15 ms in all three axes; simulates kerb strikes and minor impact events
External Short Circuit
All terminals shorted through 5 mΩ for 10 minutes; no fire, explosion, or electrolyte leakage permitted
Overcharge
REESS charged to 1.5× rated voltage; BMS must prevent hazardous event; tests cell-level protection
Thermal Propagation
Single cell forced into thermal runaway; occupant warning must be given; no catastrophic event for ≥5 minutes
Fire Exposure
External open flame applied for 70 seconds; no explosion; models vehicle underbody fire scenario
Over-discharge
REESS discharged below minimum voltage; BMS protection assessed; checks for cell reversal and venting
Thermal Propagation — The Critical Test
Thermal propagation is the spread of thermal runaway from one failing cell to neighbouring cells — the primary cause of major EV fires
R100 Rev. 3 (2021) introduced mandatory thermal propagation testing as a type-approval requirement for the first time globally
Test method: a single cell is forced into thermal runaway by overcharging, nail penetration, or resistive heating
The REESS must provide an audible or visible warning to occupants before conditions become dangerous inside the cabin
After the thermal event begins, no explosion or fire external to the REESS is permitted for at least 5 minutes — giving occupants time to evacuate
Battery pack design strategies: thermal barriers between cell groups, intumescent materials, gas venting channels directed away from occupants
5 min
Minimum time before catastrophic event is allowed
Thermal propagation testing is the single most design-impactful R100 requirement — it drives cell selection, module architecture, and pack geometry from the earliest concept stage.
Battery Management System (BMS) Requirements
The BMS is the electronic guardian of the REESS. R100 requires it to independently enforce six protection functions:
Overcharge Protection
Disconnect HV before any cell exceeds maximum voltage limit; must act before chemical degradation begins
Over-discharge Protection
Disconnect load before any cell drops below minimum voltage; prevents cell reversal and copper dissolution
Over-temperature Protection
Monitor cell, coolant, and enclosure temperatures; trigger cooling or load reduction before thermal runaway threshold
Over-current Protection
Limit continuous and peak discharge/charge currents; fuse or contactor opens on sustained overcurrent
Isolation Monitoring
Monitor insulation resistance between HV conductors and chassis; alert driver if below 100 Ω/V (DC)
State of Charge Accuracy
SoC accuracy within ±5% required — prevents overcharge/over-discharge from estimate error
IP Protection & HV Connector Requirements
Location / Condition
Required IP Rating
Meaning
Under bonnet — normal operation
IPXXB
Finger probe cannot contact live parts
Underfloor REESS
IP67
Dust-tight + immersion 1 m for 30 min
Charging inlet — connected
IPXXB
Live parts inaccessible when plug inserted
Charging inlet — disconnected
IP44 min.
Splash-proof when parked in rain
HV connectors — unmated
IPXXB + interlock
Cannot touch live pins; requires tool to disconnect under load
Post-crash (wading / flooding)
IP67
Vehicle waded through 500 mm water — no shock risk
Orange is mandatory: All HV conductors must use orange cable colour coding per ISO 6469-3 — providing instant visual identification for emergency responders.
Post-Crash Safety Requirements
After a crash event, five mandatory safety requirements apply to the vehicle’s HV system:
A
HV Bus Discharge < 60V in 5 seconds
Capacitors on the HV bus must be discharged below 60V DC (or 30V AC peak) within 5 seconds of a crash trigger. Protects first responders from electrocution.
B
No Electrolyte Spillage into Passenger Compartment
No liquid electrolyte may leak into the cabin. Limited leakage outside the vehicle is permissible (< 7% by mass in 30 min).
C
No HV Parts Ejected
No HV live components may be propelled outside the vehicle body outline during a crash — preventing projectile electrocution risk.
D
REESS Retention
The REESS must remain secured within its mounting structure under crash loads — complete ejection from the vehicle is not permitted.
E
Touch Voltage Limit
Any accessible surface after the crash must remain below 1V AC peak or 2.5V DC — the safe human touch threshold for wet conditions.
Post-crash requirements are assessed after the vehicle passes UN R94 (frontal) and UN R95 (lateral) crash tests — not a separate standalone R100 crash test.
UN R100 vs ISO 6469 Series
Aspect
UN R100
ISO 6469 Series
Type
Regulatory — legally binding
Voluntary technical standard
Scope
Type approval — whole vehicle + REESS
Design guidance for OEM engineers
Enforcement
Cannot sell vehicle without compliance
Not enforced — reference for design
Approval marking
E-mark on vehicle
No mark — conformity declaration only
Relationship
References ISO 6469 test methods
Informs R100 technical content
Type Approval Process Under UN R100
1. Application
OEM or REESS supplier applies to Technical Service (TS) and TAA with vehicle/system definition
2. Technical File
Submit: circuit diagrams, BMS specification, REESS design, IP ratings evidence, safety concept, test strategy
TAA issues E-mark (e.g. E4/100/XXXXX for Netherlands); covers specific vehicle type or REESS
6. Production Conformity
OEM demonstrates ongoing conformity via QMS audits; TAA may request CoP samples at any time
E-Mark Approval & Global Acceptance
E4
100 / 00123456
Example: Netherlands TAA (E4) · UN R100 · Approval number 123456
E-marked vehicles are accepted without re-testing in all 60+ UNECE 1958 Agreement signatory countries
Countries include: all EU member states, UK, Japan, South Korea, Australia, Russia, and more
REESS Part II approval can be granted independently — battery suppliers can certify packs for use in multiple vehicle models
OEMs must maintain technical documentation for 10 years after last date of production
Non-EU markets (India, China, US) have parallel national regulations inspired by R100 content but require separate certification
R100 and the Wider Regulatory Ecosystem
UN R94
Feeds into
Frontal crash test — vehicle must pass R94; R100 post-crash requirements are then assessed on the same crashed vehicle
UN R95
Feeds into
Lateral impact test — REESS must survive side impact without explosion or electrolyte leakage into cabin
UN R10
Parallel
EMC regulation — EV inverters and HV cables must also comply with R10 electromagnetic emission and immunity limits
UN R155
Complementary
Cybersecurity — BMS remote access and OTA update security must comply; a compromised BMS is a safety risk
ISO 6469
Technical basis
EV safety standards series — R100 references ISO 6469-1 (REESS), -3 (shock), and -4 (post-crash) for test methods
UN GTR 20
Global parallel
Global Technical Regulation on Electric Vehicle Safety — aligned with R100 content but broader in scope
Common R100 Design & Compliance Challenges
01 · Thermal Propagation Architecture
Designing modules that contain a single-cell runaway for 5+ min requires thermal barriers, venting paths, and fire-resistant materials — adding mass and cost to every pack design
02 · IP67 in Crash Conditions
Maintaining REESS IP67 after a crash event requires robust enclosure design — post-crash deformation must not compromise sealing integrity
03 · 5-Second HV Discharge
Meeting the 5-second capacitor discharge requirement whilst keeping pre-charge circuits safe for normal operation is a subtle control system engineering challenge
04 · BMS Independence & Redundancy
The BMS must reliably protect the REESS even if one protection path fails — requiring redundant measurements and diverse protection hardware
05 · Charging Interlock Reliability
Interlock systems must prevent HV under all fault scenarios — single-point failures in the interlock chain must not result in live connector exposure
06 · REESS Mounting Integrity
Battery packs must withstand crash loads without ejection — attachment design must consider both normal service loads and crash deceleration forces simultaneously
Best Practices for R100 Compliance
Concept
Confirm REESS chemistry and architecture against all Part II abuse tests early in the programme
Identify which tests require independent REESS approval vs vehicle-level approval
Design
Use orange HV cabling throughout and label all HV connectors per ISO 6469-3 from the start
Design IMD with diverse sensing paths — avoid single-point measurement failure modes
Ensure IP67 integrity through sealing design review and post-crash deformation analysis
Validation
Perform pre-compliance Part II testing before formal TS submission — identify failures early while fixes are cheap
Include thermal propagation test in the programme — it carries the highest-risk and longest remediation time
Document BMS software safety functions to ISO 26262 ASIL B or C as required
Approval
Engage the Technical Service at programme start — early test plan alignment avoids costly delays
Prepare a comprehensive technical file with full REESS schematics and BMS functional description
Plan Production Conformity procedures from launch — the TAA can audit at any time after approval
Lead time warning: Thermal propagation testing is the longest-lead compliance activity — begin cell-level screening 18–24 months before planned type approval submission.
Key Takeaways
UN R100 is the globally harmonised type-approval regulation for BEV/HEV safety — legally binding in 60+ countries under the UNECE 1958 Agreement.
Part I covers whole-vehicle HV electrical safety (shock protection, IMD, charging interlocks, post-crash); Part II covers REESS battery pack abuse safety.
Thermal propagation containment — preventing pack fire from reaching occupants for ≥5 minutes — is the defining design challenge introduced in Revision 3 (2021).
IMD and post-crash HV discharge below 60V within 5 seconds are mandatory for all HV vehicles — non-negotiable safety baselines.
IP67 sealing of the REESS is required for normal operation and must be demonstrated after crash loading — not just on a pristine test sample.
The BMS must independently enforce all six protection functions with documented functional safety — ISO 26262 ASIL requirements typically apply.
Start thermal propagation testing 18–24 months early — it is the single highest-risk, longest-lead compliance activity in any R100 programme.
References & Source Material
The content of this article is based on the following primary regulatory documents, referenced standards, and industry guidance. For any compliance programme, always consult the official current versions of the documents listed below.
Primary Regulation
UN Regulation No. 100 — Uniform Provisions Concerning the Approval of Vehicles with Regard to the Specific Requirements for the Electric Power Train
United Nations Economic Commission for Europe (UNECE). Revision 3 (2021) is the current version. The primary normative reference for all content in this article. Legally binding in all UNECE 1958 Agreement signatory countries. Freely available to download from the UNECE website.
Note: UN Regulations are freely available from UNECE — they are public documents at no cost, unlike ISO standards.
Referenced Technical Standards
ISO 6469-1:2019 — Electrically Propelled Road Vehicles — Safety Specifications — Part 1: Rechargeable Energy Storage System (REESS)
ISO. Voluntary standard defining safety requirements for the REESS — directly referenced by R100 for Part II test methods and design guidance for OEM engineers.
ISO. Covers electric shock protection requirements for EV/HEV including IP ratings, orange cable coding, connector interlock design, and isolation monitoring — the technical basis for Part I of R100.
ISO 26262:2018 — Road Vehicles — Functional Safety (Parts 1–12)
ISO. Referenced in R100 best practices — BMS software safety functions must be developed to appropriate ASIL levels (typically ASIL B or C) under ISO 26262 Part 6.
Complementary Regulations Referenced in this Article
UN Regulation No. 94 — Uniform Provisions Concerning the Approval of Vehicles with Regard to the Protection of the Occupants in the Event of a Frontal Collision
UNECE. Frontal crash test regulation — R100 post-crash requirements are assessed on the vehicle after it has undergone the R94 frontal crash test.
UN Regulation No. 95 — Uniform Provisions Concerning the Approval of Vehicles with Regard to the Protection of the Occupants in the Event of a Lateral Collision
UNECE. Lateral impact test regulation — same post-crash assessment principle as R94 but for side impacts.
UN Regulation No. 10 — Electromagnetic Compatibility for Motor Vehicles
UNECE. EMC regulation — EV inverters, HV cables, and on-board chargers must also comply with R10 emission and immunity requirements in parallel with R100.
UN Regulation No. 155 — Cybersecurity and Cybersecurity Management System
UNECE. Cybersecurity regulation — BMS remote access and OTA update security channels must comply with R155. A compromised BMS represents both a cybersecurity and a safety risk.
UNECE WP.29 — World Forum for Harmonization of Vehicle Regulations
United Nations Economic Commission for Europe. The governing body responsible for UN R100, UN R10, UN R155, UN R156, and all other vehicle regulations referenced in this article. All UN Regulations and working documents are freely available to download.
This article provides an educational overview of UN Regulation No. 100 based on its publicly available text and structure. It is not a substitute for the official regulation or accredited engineering expertise. For any vehicle development, type approval, or compliance programme, always obtain and consult the current official version of UN R100 directly from UNECE, and engage an accredited Technical Service for test planning and execution. Thermal propagation and other Part II abuse tests must only be conducted by qualified personnel in appropriately equipped facilities.
UN Regulation No. 100 — Electric Powertrain Safety | REESS | BEV · HEV | UNECE 1958 Agreement
Published by UNECE · Freely available at unece.org
