Manual Service Disconnect (MSD) for Battery Energy Storage
A manual service disconnect (MSD) is the part that lets a technician isolate a high-voltage battery circuit before maintenance, without cutting cables or waiting for the whole system to discharge. Our MSD-350 is rated 350A at 1500V DC, sealed to IP67, and built with a two-stage interlocking handle so the circuit breaks in a controlled sequence when it is pulled. It is the safety point your maintenance team should not have to improvise.
What Is a Manual Service Disconnect (MSD)?
A manual service disconnect, usually shortened to MSD, is a manually operated disconnect device that physically separates the high-voltage circuit in a battery energy storage system or electric vehicle. It is typically installed between the battery pack and the downstream electrical system, providing a defined isolation point before technicians open an enclosure, replace a module, or perform diagnostics. A battery isolator works on a similar physical isolation principle in vehicle and marine electrical systems. MSD products designed for high-voltage energy storage applications can be engineered for DC systems up to 1500V, depending on the specific model and system requirements.
Two-Stage Interlock and Controlled Disconnection
Unlike a circuit breaker, which can trip automatically in response to an overcurrent condition, an MSD is operated manually. On a two-stage design such as the MSD-350, the operating sequence separates the electrical contacts before the removable handle can be fully withdrawn. This staged mechanism helps create a more controlled disconnection process and reduces the likelihood of improper separation while the high-voltage circuit is still engaged.
The MSD-350 uses a PA66 housing with silver-plated high-conductivity copper contacts. Contact resistance is specified at ≤ 0.20 mΩ, while insulation resistance is specified above 10 MΩ at 500V DC and above 100 MΩ at 1000V DC. These electrical characteristics can be checked during product validation using appropriate test equipment before the disconnect is installed in the battery system.
Housing Material
PA66
Engineering thermoplastic housing
Contact Material
Silver-Plated Copper
High-conductivity contact system
Contact Resistance
≤ 0.20 mΩ
Low-resistance current path
Insulation Resistance
>100 MΩ @ 1000V DC
>10 MΩ @ 500V DC
Why Your Battery System Needs an MSD
Three situations justify adding a manual service disconnect to a battery system. The requirement is similar in each case: a clearly defined physical isolation point for the high-voltage DC circuit.
Maintenance
Inside a storage cabinet, the DC bus can remain energized even after the inverter has been shut down. A technician working on the battery rack needs a defined physical isolation point. A software or inverter shutdown alone should not be treated as physical DC isolation. The MSD provides a manual disconnect at the battery side of the system for service and maintenance procedures.
Emergency Isolation
When a module overheats, a connection shows abnormal temperature rise, or the battery management system reports a fault, a clearly identified manual disconnect can help isolate the affected section. The MSD provides a defined mechanical disconnection point that authorized personnel can operate in accordance with the system manufacturer’s procedures and site safety requirements.
Fault Investigation
An MSD does not replace fuses, contactors, or the battery management system. Instead, it supports the overall protection strategy by providing a clearly identifiable manual disconnect during inspection and fault investigation. Service personnel can isolate the circuit and then verify the absence of hazardous voltage using the appropriate test equipment before beginning service work.
Where a Manual Service Disconnect Is Used
The MSD-350 shows up wherever a high-voltage DC battery circuit needs a controlled break point.
Utility-Scale Storage Cabinets
Installed on the DC side between the rack and the power conversion system (PCS), allowing individual racks to be safely isolated without shutting down the entire plant.
Battery Assembly & EOL Lines
Fitted as the final component before end-of-line (EOL) testing, providing automated test stations with a safe, repeatable mechanism to disconnect the battery pack.
EV Battery Packs
Acts as the designated physical isolation point referenced throughout OEM service and workshop manuals for secure, pack-level maintenance.
Manual Service Disconnect Specifications
The MSD-350 is a single product variant built around one set of ratings, which keeps selection simple: if your system runs at or under 350 A and 1,500 V DC, this manual service disconnect fits the electrical side of the circuit.
| Parameter | Value |
|---|---|
| Model | MSD-350 |
| Rated current | 350 A |
| Rated voltage | 1,500 V DC |
| Dielectric strength | 4,000 V AC |
| Contact impedance | ≤ 0.20 mΩ |
| Insulation resistance | > 10 MΩ @ 500 V DC / > 100 MΩ @ 1,000 V DC |
| Plugging force | ≤ 75 N |
| Degree of protection | IP67 / UL94 V-0 |
| Number of mating cycles | ≥ 300 |
| Locking method | Two-stage interlocking |
| Mounting screws | M8 |
| Housing material | PA66 |
| Contact material | High-conductivity copper, silver-plated |
| Operating temperature | −40°C to +125°C |
| Storage condition | −20°C to +65°C, relative humidity below 60% |
Manual Service Disconnect Selection Guide
Because the MSD-350 carries one current rating, your selection job is to confirm that the rest of the system lines up with it. Work through this table before you send the inquiry:
| System Condition | Matches MSD-350? | What to Do |
|---|---|---|
| System voltage ≤ 1500V DC | Yes | Proceed → |
| Maximum circuit current ≤ 350A | Yes | Proceed → |
| Panel with 4×Ø13 mm mounting holes, M8 screws | Confirm against drawing | Ask for the dimensioned drawing |
| Cable 95–150 mm² | Confirm lug size | Tell us the cross-section and lug type |
| IP67 requirement | Yes | Check gasket and panel flatness |
| CE / UL / RoHS compliance | Yes | State your target market |
| Custom color or marking | Customizable | Give us the requirement |
Installation and Handling
Standard mounting procedure, electrical termination criteria, and environmental storage guidelines for the MSD-350.
Mounting & Verification Workflow
1
Check Dimensions
Confirm the panel opening and the four Ø13 mm mounting holes against the dimensioned drawing before installation.
2
Seat & Fasten
Seat the gasket correctly and secure the MSD-350 with M8 screws. Tighten evenly to compress the seal without distorting the housing.
3
Connect Cables
Attach the cable lugs using M8 bolts and tighten them to the manufacturer-specified torque value.
4
Verify Interlock
Operate and reseat the handle once to confirm that the two-stage interlock moves freely before the system is energized.
Cable Connection & Sizing
Cable connections use M8 bolts matched to the selected lug. Confirm that the cable cross-section, lug dimensions, and final assembly meet the electrical and thermal requirements of your system.
Hardware:
M8 Bolts
For 350A Rating:
95–150 mm² Cu
Verify the final conductor size against the application’s allowable temperature rise, voltage drop, installation method, and applicable electrical requirements.
Storage & Environmental Specs
Proper storage conditions help preserve the mechanical and electrical performance of the disconnect before installation.
Temperature
-20 to +65°C
Max Humidity
< 60% RH
Shelf Life
1 Year
What to Include in Your MSD Inquiry
To configure and quote the optimal MSD-350 solution on the first pass, please provide the following technical requirements:
Target Application
Energy storage cabinet (BESS), battery rack, EV battery pack, or custom power unit.
System Voltage & Current Rating
Nominal DC system voltage and maximum continuous or peak current requirement.
Cable & Lug Termination
Cable cross-section in mm² or AWG and lug type, or the relevant internal busbar connection details.
Panel Thickness & Mounting
Enclosure panel thickness, mounting surface, and required hole or cutout pattern.
Required Certifications
Target-market compliance requirements such as CE, UL, RoHS, REACH, or other applicable standards.
Quantity & Target Schedule
Required sample quantity or estimated production volume, together with your target delivery date.
Color, Marking & Customization
Housing color, laser marking, keying options, HVIL harness length, private labeling, or other project-specific customization requirements.
Selecting the Right Manual Service Disconnect (MSD) for Your System
Send us your current, DC voltage, busbar size, and cable size. We’ll recommend the right MSD with datasheet and drawings within one business day.
Battery Busbar Connector Request
Send us your working current, DC bus voltage, busbar size, cable size, and panel opening. Our team will help you select the right battery busbar connector for your system.
24H Response
Technical Selection Support
Common MSD Misconceptions
An MSD is not a switch you can treat like a standard plug. Three points come up repeatedly with buyers who are new to high-voltage disconnects:
“Any disconnect switch will do.”
The difference is in the interlock. A two-stage interlocking handle controls the disconnect sequence so the contacts separate before the handle is fully removed. The MSD-350 is designed around this sequence, which is why operating force and mating-cycle performance are specified.
“It is maintenance-free.”
Contacts and sealing materials can change with time, storage conditions, and use. The storage and handling requirements matter because a safety-related component that has remained in storage beyond its specified period should be inspected before it is installed in an energized system.
“I can mount it anywhere.”
The panel opening, mounting-hole pattern, gasket compression, and panel flatness all affect sealing performance. Installing the disconnect on a distorted or uneven mounting surface can prevent the gasket from sealing correctly and compromise the intended IP67 protection.
Why Buy MSD Connectors from Our Factory
From manufacturing and inspection to product customization, the MSD-350 is supported directly by our in-house production and engineering team.
Manufacturing & Quality Control
We have made energy storage and new energy connectors since 2015. Our factory covers 6,800 m² with CNC machining, injection molding, and assembly lines under one roof. The factory is certified to ISO 9001, IATF 16949, and ISO 13485, and our outgoing inspection pass rate is above 99%. Every MSD-350 ships with inspection reports and material certificates on request.
6,800 m²
Factory
Since 2015
Manufacturing
>99%
Inspection Pass Rate
Customization & Engineering Support
We also build custom variants. If your cabinet needs a different mounting pattern, a different handle color, or a specific marking, we can adjust the product around the same 350 A / 1,500 V DC core. Tell us the requirement and we will confirm feasibility before tooling anything.
FAQ
A manual service disconnect is a manually operated switch that isolates the high-voltage DC circuit in a battery storage system or an EV so technicians can work safely. It is pulled by hand to break the circuit before maintenance or emergency shutdown.
The two-stage interlocking handle breaks the circuit in a controlled sequence: the contacts open first, then the handle releases fully. This limits arcing and makes the disconnect sequence repeatable and safe.
A circuit breaker protects against overcurrent and trips automatically. An MSD is a manual isolation device: it does not protect the circuit, it guarantees that the circuit is off while people work on it.
350A rated current, 1500V DC rated voltage, 4000V AC dielectric strength, IP67 / UL94 V-0, with two-stage interlocking and M8 mounting.
Yes, the MSD-350 is rated IP67 when mounted on a flat panel with the gasket seated correctly, and the housing is UL94 V-0 flame retardant.
At least 300 mating cycles, with a plugging force of 75N or less.
Yes. Mounting pattern, color, and marking can be adjusted around the same 350A / 1500V DC core. Send us your requirement.
