LCN SEM7850 Magnetic Holder

The LCN SEM7850 is the standard profile recessed wall mount version of LCN's SEM7800 Series electromagnetic door holder. The diecast magnet body mounts into the wall at the door opening. An armature plate mounts on the door. When the building supplies power to the magnet circuit, the electromagnetic field pulls the armature and holds the door open at 35 pounds of holding force. When the fire alarm panel interrupts that circuit, the field collapses, the armature releases, and the door closer on the door shuts the door completely.

The SEM7850 is the specific electromagnetic holder called out in LCN's 4004T wall pocket track door closer/holder system specifications. When the LCN 4004T is specified for an application with electromagnetic hold-open, the SEM7850 is the wall magnet paired with it. The two work together: the 4004T controls the closing force and speed; the SEM7850 provides the electromagnetic hold-open function. If you're specifying or replacing the wall magnet on a building with LCN 4004T closers, the SEM7850 is the correct part.

All SEM7800 Series magnets are UL listed for smoke barrier and labeled fire doors, certified under ANSI A156.15. Fail safe: the door releases when power fails. No special mode is needed. For all LCN door closers and holder accessories, browse our door closers catalog. For all electromagnetic holders, view our electronic hardware catalog.

SEM7850 vs SEM7840: Standard Profile vs Low Profile

Both the SEM7850 and SEM7840 are recessed wall mount electromagnetic holders in the LCN SEM7800 Series with identical dimensions (2" x 4" x 1-1/2"), identical 35-pound holding force, identical tri-voltage design, and identical fire door UL listing. The profile designation is the physical distinction.

The SEM7840 is the low profile version, designed for installations where minimal projection or recess depth is the priority. The SEM7850 (this product) is the standard profile version, the configuration called for in standard LCN door closer/holder system pairings including the 4004T.

When a hardware schedule or LCN documentation references the SEM7850 specifically, order the SEM7850. When the schedule references the SEM7840 specifically, order the SEM7840. If neither is specified and you're replacing an existing magnet, confirm the existing unit's model number before ordering to ensure the replacement matches the installed profile.

Fail Safe and Fire Alarm Integration

The SEM7850 holds as long as power flows. The building's fire alarm panel monitors the circuit. When the alarm activates, the panel cuts power to all held-open fire doors simultaneously. Every SEM7850 in the building releases at the same moment. The door closer on each door shuts the door and latches it. This is the required NFPA 80 behavior for fire-rated corridor and smoke barrier doors: they must close and latch automatically when the fire alarm fires.

The outlet box for the wall recess is not included with the SEM7850 and must be sourced and installed separately.

LCN SEM7850 Specifications

• SKU: SEM7850

• Also known as: LCN SEM7850, SEM 7850, EM7850AL, SEM7850ALUM, SEM7850DKBRZ, lcn 7850, lcn magnetic door holder, lcn magnetic hold open, sem7800 wall magnet

• Series: LCN SEM 7800 Series, Sentronic

• Type: Electromagnetic door holder, standard profile recessed wall mount

• Compatible closer system: LCN 4004T wall pocket track door closer/holder (specified pairing)

• Hold force: 35 lbs

• Dimensions: 2" (51mm) x 4" (102mm) x 1-1/2" (38mm)

• Housing: Die cast

• Mounting: Standard profile recessed wall mount

• Fail mode: Fail safe; releases when power is interrupted

• Voltage: Tri-voltage; 24V AC/DC or 120V AC/DC

• UL: Listed for smoke barrier and labeled fire doors

• ANSI: A156.15

• Includes: Die cast housing, cover, armature, WMS screw pack

• NOT included: Outlet box (must be sourced and installed separately)

• Closer requirement: Requires separate door closer for door closing function

• Finishes: Aluminum (BHMA 689), Dark Bronze (BHMA 695)

• Resources: SEM7800 Catalog Information in Resources section