Manual Service Disconnect (MSD) for Battery Storage and EV Packs
A manual service disconnect (MSD) is a non-fused isolator that physically separates high-voltage DC battery circuits in BESS racks and EV packs before maintenance. Rated at 350 A and 1,500 V DC with IP67 sealing, our MSD-350 uses a two-stage interlocking handle to provide a lockable, zero-voltage isolation point after system shutdown.
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.
What Is a Manual Service Disconnect (MSD)?
MSD stands for Manual Service Disconnect — a hand-operated high-voltage isolator that breaks the DC circuit in a battery storage system or EV pack so technicians can service it safely. 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 usually sits between the battery pack and the rest of the system, so a technician has one defined point to break before opening an enclosure or pulling a module. 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 are built for DC systems up to 1500V DC.
Application: High-voltage battery systems in battery energy storage systems (BESS) and electric vehicles, where a defined manual disconnection point is required.
Two-Stage Interlock and Controlled Disconnection (with Optional HVIL)
A circuit breaker trips on its own when current runs too high. An MSD moves only when someone pulls it. On a two-stage design such as the MSD-350, the mechanical latch separates the main electrical contacts in Stage 1 before the removable handle can be fully withdrawn in Stage 2. You cannot pull the handle free until the contacts have separated, so the two stages cannot be reversed by accident. For EV battery packs and smart BESS racks requiring a High-Voltage Interlock Loop (HVIL), Stage 1 can be configured with an HVIL signal circuit that opens first—signaling the BMS or PCS to trip main contactors—before Stage 2 physically separates the 1,500 V DC bus.MSD-350: Key Technical Specifications
Contact Resistance
≤ 0.20 mΩ
Maximum specified resistance
Insulation Resistance
> 10 MΩ
At 500V DC
Insulation Resistance
> 100 MΩ
At 1000V DC
The MSD-350 uses a PA66 housing with silver-plated high-conductivity copper contacts. All three values can be checked with standard test equipment before the part goes into a live system.
MSD, Contactor, Breaker or Fuse: What Each One Does
Four devices can sit on the same DC bus, and each one does a different job. Swapping one for another, or expecting one of them to cover the MSD’s role, is a common specification error.
| Function | MSD-350 | Contactor | Circuit breaker | Fuse |
|---|---|---|---|---|
| Operated by | Technician, by hand | Control signal | Manual or automatic trip | Fault current |
| Resets without parts | Yes, reseat the handle | Yes, by signal | Yes, after trip | No, replace it |
| Breaks current under load | No, isolate the load first | Yes | Yes | Yes, once |
| Role in the DC bus | Isolation point for service | Normal switching | Overcurrent protection | Short-circuit protection |
| Rated for repeated service use | Yes, ≥300 mating cycles | Yes | Yes | No |
An MSD does not replace any of the other three, and none of them gives a technician a place to put a lock. That is the job the MSD-350 takes. Whichever device isolates the circuit, verify the absence of hazardous voltage before work starts.
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
It sits on the DC side between the rack and the power conversion system, so one rack can be isolated without taking the plant down.
Battery Assembly & EOL Lines
It goes in last on the pack line, before end-of-line testing. The test station then has one repeatable way to disconnect the pack.
EV and Prototype Battery Packs
EV packs need the same thing: one point where the workshop isolates the pack before service. On production vehicle programs, HVIL circuits and USCAR / SAE test documentation are quoted per project, so tell us the required standard at inquiry stage.
Manual Service Disconnect Specifications
The MSD-350 is available in one version with one set of ratings. For the electrical ratings, it is suitable for systems operating at or below 350 A and 1,500 V DC.
| 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 | M5 × 14, 3 N·m |
| Wiring screw torque (M8) | 12 N·m |
| Weight / Dimensions | Weight not specified; see dimensional drawing |
| Housing material | PA66 |
| Contact material | High-conductivity copper, silver-plated |
| Operating temperature | −40°C to +125°C |
| Storage / shelf conditions | −20 °C to +65 °C, below 60 % RH; shelf life 1 year |
Manual Service Disconnect Selection Guide
The MSD-350 has a single current rating. Use this checklist to confirm that the rest of your system is compatible before sending an inquiry.
| System condition | MSD-350 compatibility | What to do |
|---|---|---|
| System voltage ≤ 1500 V DC | Compatible | Proceed to the next check. |
| Maximum circuit current ≤ 350 A | Compatible | Proceed to the next check. |
| Panel mounting: 4 × Ø13 mm holes | Confirm against the drawing | Ask us for the dimensioned drawing and confirm the M8 fasteners. |
| Cable cross-section: 95–150 mm² | Confirm lug compatibility | Tell us the cable cross-section and lug type. |
| IP67 requirement | Designed for IP67 | Check gasket condition and panel flatness during installation. |
| CE / UL / RoHS documentation | Available on request* | Tell us your target market and which documentation you need. |
| Custom color or marking | Customization available | Include your color or marking requirements in the inquiry. |
Comparing connector families for the same cabinet? Read our 1500 V BESS connector selection guide for an overview of the DC bus.
Installation and Handling
Four steps, in order. The panel opening is the expensive one to get wrong.
Mounting & Verification Workflow
Check Dimensions
Confirm the panel opening and the four Ø13 mm mounting holes against the dimensioned drawing before installation.
Seat & Fasten
Seat the gasket correctly and secure the MSD-350 with M8 screws. Tighten evenly to compress the seal without distorting the housing.
Connect Cables
Attach the 95–150 mm² cable lugs using M8 bolts and tighten them to the torque specified on the approved product drawing (typically 12–15 N·m for M8 high-voltage terminals) to maintain contact impedance ≤ 0.20 mΩ.
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
The M8 bolts take the lug you specify. Check the cable size against your own temperature rise and voltage drop budget.
Need sizing confirmation? Send us your exact cable cross-section and lug specifications with your inquiry, and our team can help confirm mechanical fit.
Storage & Shelf Conditions
Temperature−20°C to +65°C
Relative humidityBelow 60%
Shelf lifeOne year
Keep away fromChemicals & heavy loads
Keep the part between −20°C and +65°C, below 60% relative humidity, away from chemicals and heavy loads. Shelf life is one year, and units stored longer should be re-inspected before they go into a live system. These figures describe warehouse and transport conditions, not the operating limit of the part, which is −40 °C to +125 °C.
What to Include in Your MSD Inquiry
To quote the right MSD-350 the first time, send us these details:
-
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.
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Panel Thickness & Mounting
Enclosure panel thickness, mounting surface, and required hole or cutout pattern.
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Required Certifications
Target-market compliance requirements such as CE, UL, RoHS, REACH, or other applicable standards.
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Quantity & Target Schedule
Required sample quantity or estimated production volume, together with your target delivery date.
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Color, Marking & Customization
Housing color, laser marking, keying options, HVIL harness length, private labeling, or other project-specific customization requirements.
MSD-350 · TECHNICAL SUPPORT
Selecting the Right Manual Service Disconnect for Your System
Send us your working current, DC voltage, busbar dimensions, cable size and panel opening. Our team will help confirm whether the MSD-350 fits your application.
Response within 12 hours Technical selection support
MSD-350 APPLICATION SUPPORT
Request a Quote
Share your system ratings and installation details. Our team will help review the MSD-350 for your application.
One business day response Technical support
Why Buy MSD Connectors from Our Factory
The MSD-350 is made, inspected and customized in our own plant.
Since 2015
Manufacturing energy storage and EV connectors
6,800 m²
In-house CNC, injection molding, and assembly plant
>99%
Outgoing factory inspection pass rate
IATF 16949
Certified quality system (plus ISO 9001 & ISO 13485)
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. Product certificates for CE, UL and RoHS are available on request.
ISO 9001
IATF 16949
ISO 13485
CE documentation on request
UL documentation on request
RoHS documentation on request
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.
Frequently Asked Questions
Answers to common questions about the MSD-350 manual service disconnect.
Need an MSD for your battery system?
Request the MSD-350 specifications for your application.