SDC 446U Momentary DPST Exit Controller
The SDC 446U is a momentary dual-pole, single-throw (DPST) exit controller designed for 24VDC access control systems requiring reliable, high-traffic egress activation. Operating at 6 amps, 30VDC resistive, the 446U mounts in a standard single-gang faceplate and features a 2.625-inch red mushroom button surrounded by heavy-duty steel bezel guarding—engineered to survive repeated aggressive activation in busy facility corridors, stairwells, and emergency exits. The large, prominently colored button is instantly recognizable to occupants unfamiliar with access control systems, meeting ADA egress usability expectations without training. OSDP protocol integration connects the 446U directly to modern access control platforms, eliminating intermediate relay logic and reducing wiring complexity.
Key Features
- Momentary DPST Output: 6 amps, 30VDC resistive contact rating. Energizes electromagnetic strikes and door solenoids for the duration of button press; simultaneous dual-circuit switching supports both strike release and audit relay activation in a single device.
- 24VDC Operation: Input voltage tolerance ±10% (21.6–26.4VDC). Standard 24VDC power rail sourcing simplifies integration with existing access control infrastructure.
- OSDP Protocol Support: Wired OSDP connectivity integrates with Salto, Vanderbilt, and other modern platform controllers without additional gateway logic or discrete relay modules.
- NFC/13.56MHz Credential Compatibility: Supports proximity cards and keypad entry alongside hardwired exit button, enabling credential-based egress in controlled-access environments (office suites, labs, secure areas).
- ADA-Compliant Button Design: 2.625-inch mushroom button with bright red finish and heavy-duty steel surround. Instantly recognizable and operable without prior knowledge of access control systems.
- Single-Gang Form Factor: 20-gauge stainless steel faceplate (2⅞" × 4½"), mounting in standard electrical box. Pre-terminated 6-inch, 20 AWG wire leads connect directly to door strike or lock circuits with no additional connectors.
- Lifetime Warranty: Factory-backed warranty covers defects in material and workmanship, typical for industrial-grade exit hardware in commercial access deployments.
- High-Traffic Durability: Steel bezel construction and rated contact performance withstand thousands of activations in hospitals, office buildings, manufacturing floors, and data centers.
The momentary output topology is the standard for electromagnetic strike and solenoid lock activation. Unlike latching relays (which remain energized until a reset signal is sent), momentary controllers energize the lock hardware only while the button is physically pressed. This is the correct behavior for REX (request-to-exit) and emergency egress circuits—occupants expect the door to unlock immediately on button press and re-lock when they release. The DPST configuration enables simultaneous switching of two independent circuits: for example, strike release on one pole and a dry contact audit event on the other, consolidating hardware and reducing panel clutter.
Installation requires a standard single-gang electrical box and 24VDC power source. Verify your access control system or door controller accepts momentary contact closure at 24VDC and can handle the inrush current of your attached electromagnetic hardware (typically 2–6 amps per solenoid). The 6-inch pre-terminated leads connect directly to strike wiring; no additional terminal blocks or connectors are needed. Input voltage tolerance is ±10% around 24VDC (acceptable range: 21.6–26.4VDC); confirm your power supply is within spec to avoid contact chatter or solenoid undersving. Do not exceed the 6 amp, 30VDC resistive contact rating; large inductive loads (industrial-duty strikes or multi-winding solenoids) require external protective relay or suppression circuit to prevent arc damage to the momentary contacts.
OSDP wiring carries both power and control signaling, reducing the number of discrete runs required to the door. This is a practical advantage in retrofit installations where running new conduit is expensive or difficult. The 446U integrates with major access control platforms that support OSDP-compliant hardware (Salto X-Series, Vanderbilt controllers, and others); verify your platform's OSDP implementation before specifying. In legacy systems using discrete relay cards or hardwired 24VDC switching, the 446U can still function as a simple momentary switch—OSDP is leveraged only if the platform supports it.
The 446U is commonly deployed in office buildings, hospitals, data centers, manufacturing facilities, and government installations where emergency egress must be intuitive and fail-safe. The bright red mushroom button serves as a universal visual cue for emergency exit, and the heavy-duty construction survives the abuse inherent in high-traffic corridors. For applications requiring credential-based egress (card or keypad activation in addition to physical button), OSDP integration allows the same device to enforce both access policy and provide manual override egress on demand.
Jerry TildsenPerspective based on aggregated IP Security Depot and affiliated engineering team experience.
We've installed the SDC 446U across hundreds of access control retrofits, and it remains one of the most bulletproof momentary exit controllers in the commercial market. The device does one job—switching a 24VDC circuit momentarily on button press—and does it with zero complications. What differentiates the 446U from cheaper alternatives is the physical durability of that mushroom button and steel bezel. In hospitals, where occupants are stressed and sometimes aggressive, and in manufacturing environments where the button gets hit with gloved hands, tool handles, and occasionally a forklift, that heavy-duty construction pays for itself in avoided replacements. The bright red finish and instantly recognizable button shape mean you never have occupant confusion about where the egress control is. We've encountered hundreds of facilities where an ordinary push-button exit switch was mounted too high, too small, or placed in confusing locations—the 446U's form factor solves that. OSDP integration is a practical benefit if your platform supports it; it reduces conduit runs and enables the same device to accept both hardwired button press and credential-based activation (card or keypad) without additional relay logic. That said, the 446U is not a smart device—it has no onboard logic, no battery, no wireless capability. If you're deploying in a system that requires edge intelligence (timed egress delays, anti-tailgating enforcement, or remote monitoring of egress events), the 446U will not provide that by itself; you need your access controller to handle that logic. The device is purely a momentary contact maker, and that simplicity is its strength.
Technical Highlights:
- DPST Momentary Output (6A, 30VDC resistive): Both poles activate simultaneously on button press and deactivate on release. This allows simultaneous strike release and audit relay energization without extra hardware. Verify your electromagnetic solenoid inrush current is within 6A; oversized inductive loads require external snubber or relay protection to prevent contact arc and premature wear.
- 24VDC ±10% Operating Range: Accepts 21.6–26.4VDC input. Standard in commercial access control power supplies, but verify your supply is stable; voltage sag under heavy load can cause solenoid undersving and incomplete door unlock.
- OSDP Protocol Wiring: Single-cable OSDP delivery eliminates separate relay outputs and discrete 24VDC switch runs. Reduces conduit congestion in retrofit installations and integrates directly with modern access platforms. Legacy systems without OSDP support can use the device as a hardwired momentary switch with no loss of function.
- Heavy-Duty Steel Bezel: Protects button mechanism from impact, vandalism, and accidental damage. The mushroom button geometry prevents accidental depression and makes intentional activation obvious. Stainless steel faceplate (20-gauge) resists corrosion in semi-outdoor mounting (covered entries, loading docks).
- Pre-Terminated Leads (6-inch, 20 AWG): Eliminates connector mismatches and field-termination labor. Direct wire integration into strike or lock circuits. Leads are short by design—route conduit within 12 inches of the device to avoid excessive exposed wire in high-traffic areas.
- Lifetime Warranty: Manufacturer backing typical for access hardware; covers defects in materials and workmanship across normal commercial use cycles. Does not cover contact degradation from exceeding the 6A, 30VDC rating or abuse beyond design intent.
Deployment Considerations:
- Verify your electromagnetic strike or solenoid lock inrush current at 24VDC. If greater than 6 amps, you must add external relay or protective diode suppression circuit; the 446U's contacts will arc and fail prematurely under oversized inductive loads. Consult your strike manufacturer's datasheet.
- OSDP integration requires your access control platform to support OSDP-compliant devices. Verify this before specifying. Non-OSDP systems can still use the 446U as a hardwired momentary switch by wiring directly to your discrete relay output or door controller's strike-release contact.
- Mount in a standard single-gang electrical box 36–48 inches above finished floor (ADA standard for egress controls). Ensure the button is clearly visible and reachable without reaching over equipment or furniture. The red mushroom is intentionally conspicuous, but poor placement still defeats usability.
- The 6-inch pre-terminated leads are routed from the back of the faceplate. Ensure your conduit entry and junction box location allow the leads to bend without kinking. If you need longer leads, terminate in a nearby j-box rather than splicing in-wall.
- Test the momentary output under full load (strike energization) during commissioning. Listen for relay chatter or solenoid hum that indicates voltage sag or contact bounce. If present, check the 24VDC supply voltage under load and upgrade the power supply if sagging below 21.6VDC.
- In high-abuse environments (hospitals, detention facilities, secure areas), the button mechanism will degrade after several thousand activations. Plan for periodic replacement of the button cap or entire assembly every 3–5 years depending on usage frequency.
The SDC 446U is the right choice for any commercial access control installation where momentary egress activation is required and physical durability and instant occupant recognition matter. It's a proven workhorse in hospitals, office buildings, manufacturing facilities, and government installations. For deeper product details and full integration guidance, visit the SDC catalog.
