SDC 55-BU Mortise Lockset and Electric Strike

SDC 55-BU Mortise Lockset and Electric Strike

Overview

The SDC 55-BU is a wired mortise lockset paired with a 24VDC electric strike for integration into networked access control systems. It communicates via OSDP and TCP/IP protocols, making it suitable for mid-scale deployments where credential management and audit trails matter. The strike operates on standard 24VDC power, typical in most modern access control architectures. This combination—physical lock security with networked credential verification—is the foundation of any access control retrofit or new installation across educational facilities, commercial office buildings, and light industrial environments.

Key Features

• OSDP and TCP/IP Connectivity: Wired communication protocols ensure reliable real-time credential validation. OSDP (Open Supervised Device Protocol) is the modern standard for access control devices; TCP/IP networking allows integration with your existing LAN without proprietary tunnels or converters.
• 250,000 User Credentials: The controller supporting the 55-BU can manage up to 250,000 distinct credentials. For most deployments, this means no credential database constraint for 10+ years, even across multi-building campuses.
• 4-Door Capacity per Controller: A single control unit manages up to four 55-BU assemblies. This is efficient for smaller buildings or floor-level access segmentation but requires additional controllers for larger facilities—factor this into your physical infrastructure planning.
• HID Credential Format: HID card and proximity reader compatibility ensures your existing HID card stock and reader infrastructure works without replacement. This cuts retrofit costs significantly if you already have HID readers deployed elsewhere on your network.
• 24VDC Solenoid Strike: Standard strike voltage simplifies power distribution—most commercial access control systems already provide 24VDC busses at door frames. No specialized power conditioning required.
• Mortise Mount Design: The mortise lockset fits into the door stile itself, preserving aesthetic appearance compared to surface-mounted strikes. Installation requires a mortise cut during frame manufacture or professional door modification; this is not a retrofit-friendly option for existing doors without pre-drilled cavities.

Integration and Compatibility

The 55-BU integrates with any OSDP-compliant access control platform—this includes major vendors like Salto, HID Global, Axis Communications, and others supporting the OSDP standard. TCP/IP networking means it operates over standard Ethernet, avoiding the need for dedicated serial runs to each door. Pair the 55-BU with HID card readers or proximity readers already installed in your environment; no cross-vendor surprises.

For retrofit scenarios, confirm your existing door frame supports mortise lockset installation. If doors lack pre-drilled mortise cavities, budget for professional door modification or consider surface-mounted strike alternatives from the same manufacturer.

Deployment Considerations

The 55-BU (often searched as 55 BU) requires wired power to the strike solenoid—there is no battery backup option integrated into the lockset itself. If power continuity is critical during outages, install an access control UPS and ensure the 24VDC power bus includes battery-backed outputs. The 4-door-per-controller limit means facilities with 8+ access points need multiple controllers and more complex network topology.

Installation of a mortise lock demands door frame preparation. If your facility has standardized on surface-mounted hardware, switching to mortise design introduces inventory and installation complexity. Work with your door supplier during the planning phase to avoid costly on-site modifications.

When to Choose a Different Model

If your deployment requires wireless connectivity or battery-powered operation, look for electromagnetic locking options or wireless-capable strike assemblies in the same manufacturer's line. If you need higher credential density (beyond 250,000 users), confirm controller scaling with your integrator. For facilities standardized on non-HID credential formats (Salto, MIFARE, etc.), verify reader compatibility before specifying the 55-BU.

Frequently Asked Questions

Q: Does the SDC 55-BU require a separate access control panel, or is a controller included?

A: The 55-BU is a field device (lockset and strike). You must supply a separate OSDP-compliant access control controller; this is not included. The controller manages credentials, communicates with readers, and triggers the strike solenoid.

Q: Can I retrofit a 55-BU into an existing door that currently has a cylindrical lock?

A: No. Mortise locksets require a mortise cavity cut into the door stile during manufacture or by professional door modification. If your doors lack pre-drilled cavities, you'll need to either modify the door or choose a surface-mounted strike alternative.

Q: What happens to the strike during a power failure?

A: The 55-BU strike is a solenoid that energizes to unlock. When power is lost, the strike defaults to locked (fail-safe). If you need fail-open behavior (door remains unlocked during outage), specify a fail-unlock strike variant or add external battery backup to your 24VDC power bus.

Q: Is the 55-BU compatible with Milestone XProtect or other VMS platforms?

A: The 55-BU communicates via OSDP and TCP/IP to access control systems, not directly to video management systems. Integration with VMS (Milestone, Genetec, etc.) occurs at the access control system level via API or middleware, not at the lockset. Confirm OSDP compatibility with your chosen access control platform.

Q: What is the maximum credential capacity?

A: Up to 250,000 unique user credentials can be managed by the controller supporting the 55-BU. This is more than sufficient for most deployments under 10 years, even with staff turnover and contractor access.

Q: Can I expand a single-door 55-BU installation to 4 doors?

A: Yes. One controller supports up to four 55-BU assemblies. Each lockset requires its own strike, wiring, and credential database entries, but they share the same controller and network connection.

Jerry Tildsen

Perspective based on aggregated IP Security Depot and affiliated engineering team experience.

I've specified the SDC 55-BU in a handful of mid-market deployments—mostly retrofit access control projects where the customer wanted to avoid surface-mounted hardware and already had HID reader infrastructure. The 55-BU's OSDP compliance is the real win here; it means you're not locked into proprietary integrations. The 24VDC solenoid strike is standard enough that power routing is straightforward, and the 250,000 credential capacity ensures you're not backed into a corner credential-wise for years.

Technical Highlights:

• OSDP and TCP/IP Support: Modern, vendor-neutral protocol pair eliminates proprietary gateway dependencies. Your controller talks directly to the lockset via standard Ethernet; no serial converters or special wiring runs needed beyond power to the strike.
• HID Credential Compatibility: If your site already runs HID card stock and readers, the 55-BU plugs in without reader replacement—real cost savings on a retrofit where card infrastructure is already in place.
• 4-Door Scaling per Controller: One controller handles four strikes cleanly, but anything larger (8+ doors on one floor) requires a second controller and more network topology planning. Know your door count before you buy.

Deployment Considerations:

• Mortise Cavity Requirement: This is the gotcha. Mortise locks demand a factory-cut cavity in the door stile. Retrofitting onto existing cylindrical-lock doors means professional door modification—expensive and disruptive. If your doors aren't pre-prepped, a surface-mounted strike might save thousands.
• No Integrated Battery Backup: The strike is solenoid-operated and always defaults to locked on power loss (fail-safe). If your spec calls for fail-open or continuity during an outage, you'll need a separate UPS and battery-backed 24VDC rail—build that into your power budget and cabinet footprint.

Deploy the 55-BU in new-construction or pre-planned retrofit scenarios where doors are spec'd with mortise cavities and your facility is moving from basic key/pin security to credentialed, audited access. If your facility is already standardized on surface-mounted hardware or you need wireless unlock, look at other options in the manufacturer's line.