Inside the Manual Service Disconnect (MSD): Delivering Safe, Custom Solutions for EV Power Systems

Published by Chief Enterprises on May 29th 2025

As electric vehicles (EVs) continue to expand across global markets, the importance of safe, high-voltage assemblies is growing. One of the most critical components in any EV power system is the Manual Service Disconnect (MSD). This safety device allows secure disconnection of the high-voltage battery during servicing or emergency situations.

In this article, we explain what MSDs are, why they are essential to EV design, and how Chief Enterprises Europe supports high-voltage safety with custom MSD assemblies for next-generation mobility platforms.

What is a Manual Service Disconnect (MSD)?

An MSD is a mechanical switch integrated within the high-voltage battery pack or distribution unit. It provides a safe, manual method of disconnecting the high-voltage circuit during maintenance or an emergency event. Most MSDs are touch-safe, housed in removable enclosures, and often incorporate high-voltage fuses for added safety.

Located near the battery or power distribution centre, MSDs allow service technicians to safely isolate the power system. Assemblies are typically rated up to 1000 VDC, making them suitable for use in passenger EVs, commercial fleets, electric buses, and industrial electric vehicles.

Why MSDs Are Critical in EVs:

Safety for Technicians and First Responders

MSDs prevent unintentional system energisation during servicing or after an accident, protecting those working near high-voltage circuits.

Compliance with International Standards

MSDs support compliance with key safety regulations such as ISO 6469 and SAE J2929, required for EV development and homologation.

Efficient Maintenance and Diagnostics

A dedicated disconnect point simplifies servicing, allowing for safe fault diagnosis, component replacement, and validation of safety systems.

Chief Enterprises’ MSD Assembly Process:

What Sets Our Assemblies Apart

Each MSD assembly is hand-built with attention to mechanical robustness, electrical safety, and system integration. We offer:

Custom-designed enclosures
Modified off-the-shelf options
Support for various EV systems

Assemblies feature high-quality components from trusted manufacturers such as Amphenol Sine and Amphenol Industrial PCD, ensuring full compatibility and durability under demanding conditions.

What's Included in a Chief MSD Assembly

MSD Housing and Connector: Available with venting, heat sinking, and custom mounting provisions..
High-Voltage Cabling: Supplied in custom lengths and terminated to suit application-specific routing and layout needs.
Protective Features: Labelled and sealed assemblies using heat shrink, potting, and cable protection where required.

Quality Control and Testing

Each assembly undergoes full inspection and performance validation, including:

Continuity and insulation resistance tests
Visual inspection and torque checks
IP67 ingress protection validation
Optional full testing for safety-critical applications

Customization and Flexibility:

Built to Specification

We design to your electrical and mechanical requirements, with configurable cable gauges, colours, lengths, and layout options. Suitable for both individual units and integrated harnesses.

Rapid Prototyping

Support is available for fast development builds and test-stage validation.

Low- to Mid-Volume Production

Ideal for start-ups, niche vehicle platforms, and fleet electrification programmes.

Why Partner with Chief Enterprises:

Engineering Collaboration

We provide DFM input, layout advice, and live technical support to streamline the design-to-assembly process.

Secure Supply Chain

We work with leading suppliers including Amphenol, TE Connectivity, and others to ensure component availability and supply continuity.

European Support and Distribution

While assemblies are currently built in the US, Chief Enterprises Europe offers full commercial support, logisitcs coordination, and design input for EU-based customers.