Ensuring safety in high-voltage environments is paramount for technicians working on electric vehicles (EVs). To address this issue, the battery pack of an EV is equipped with a Manual Service Device (MSD), which disconnects the high-voltage circuit to facilitate maintenance and other work in a relatively safe state, while also quickly disconnecting the circuit in the event of a short circuit.

Given the importance of the MSD for ensuring safety, its design and selection must be given careful consideration. The basic working principle of the MSD is to install it in the main circuit with a built-in high-voltage fuse and high-voltage interlock (HVIL) function. When an external short circuit occurs, the fuse will blow to cut off the high voltage circuit, and when the high voltage needs to be disconnected manually, the HVIL will be disconnected first, followed by the high voltage circuit.

The design of the MSD must ensure that it can be disconnected manually without any tools and the number of connections must be at least 50 times, while also meeting the protection level of IPXXD when installed and connected. In addition, the MSD itself must meet IP67 and IP6k9k to ensure the Pack meets the requirements of IP67 or IP6k9k airtightness. The MSD's materials, except for the fuse and HVIL connectors, must meet the fire resistance level of UL94 V0 to prevent external fire from entering the Pack.

The MSD's functional requirements include operating temperature range, on-load cut-off capability, chemical corrosion resistance, and mechanical strength reliability. When selecting an MSD, the rated voltage, load continuous current, load peak current capability, and response time should be considered.

With the industry's gradual platformization, MSD categories are becoming fixed, mainly based on maximum voltage and high current parameters. MSDs act as safety guards for the battery pack, protecting against safety risks of high voltage and high current. They must safeguard personnel and other parts of the vehicle from the outside and protect the battery pack from short-circuit hazards from the inside while avoiding any unnecessary failures during the entire life cycle of the vehicle.