About this item
The Dormakaba EM504 is that device: an electromagnetic door holder that holds a fire door open using magnetic attraction between the wall-mounted magnet body and the door-mounted catch plate, and releases the door instantly when the fire alarm system cuts power to the unit.
The EM504 is a semi-flush unit, meaning the magnet body mounts partially into the wall rather than protruding fully on the surface. This creates a lower-profile installation that coordinates with clean corridor aesthetics while maintaining the same holding function. The long catch accommodates door-to-wall spacing where the door face and wall are further apart than standard mounting conditions. Optional extension rods extend the catch plate further for even deeper door-to-wall conditions on non-standard door swings. For all door holders, stops, and electromagnetic hold-open hardware, browse our door stops and holders catalog.
How Electromagnetic Door Holders Work with Fire Alarm Systems
The EM504 connects to the building's fire alarm system through the fire alarm panel's supervised relay output. In normal operation, the fire alarm panel supplies 24V DC or AC to the EM504 (or 120V AC in older systems). The energized magnet holds the catch plate on the door face, keeping the door in the open position. The door closer is under tension but held back by the magnet.
When the fire alarm activates, the fire alarm panel cuts power to all connected door holders simultaneously. The EM504 releases in milliseconds. The door closer, no longer opposed by the magnet, swings the door closed. The corridor is automatically sealed without any manual intervention from building occupants or staff.
The "fail safe" principle is built into this: the door is held open only while power is supplied. Power loss of any kind, whether fire alarm activation, a tripped circuit breaker, or a power outage, releases the door. This is the code-required behavior for electromagnetic door hold-open devices on fire-rated openings.
Dormakaba EM504 Technical Specifications
SKU: EM504 24120 689. Also known as: Dorma EM504, EM50424120, EM504689. Series: Dormakaba EM Series. Type: Electromagnetic Door Holder. Mount: Semi-Flush, wall or floor-mounted styles. Catch: Long Catch. Voltage: Dual voltage, 24 VAC or DC and 120 VAC (field selectable). Holding force: 15 to 25 lb nominal. Residual magnetism: Low (allows easy manual release). Manual release: Yes, doors can be manually pulled from the hold-open position at any time. Current draw: Low draw; saves on power supply and backup battery sizing. Operation: Silent. Extension rods: Optional, fits standard catch plate for deeper door-to-wall conditions. All electrical values: +10% to -15% tolerance. Finish: 689 Aluminum. ANSI/BHMA: A156.15 Grade 1 certified. UL/CUL: Listed under continuing reinspection programs. CSFM: California State Fire Marshall approved.
Dual Voltage: What It Means for Specification and Stocking
The EM504 accepts 24 VAC, 24 VDC, or 120 VAC without any internal modification or jumper change. On new construction, 24V DC from the fire alarm panel is the standard connection. In older buildings where the door holder circuit was wired for 120V AC, the same EM504 works without requiring a transformer or voltage converter. One model number covers both voltage environments, which simplifies procurement for facilities running mixed electrical systems and reduces the number of separate part numbers required in maintenance inventory.
Can the EM504 Be Repaired?
If an existing EM504 is no longer holding the door or releasing slowly, two issues are most common: corrosion or debris on the armature catch face reducing magnetic contact, or a failed coil. Armature cleaning is a field-serviceable maintenance task. Coil failure typically requires unit replacement. The EM Series PDF catalog is available under the Resources section on this page for full wiring diagrams, dimensional drawings, and technical service information.
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