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LCN SEM7840 Heavy Duty Door Holding Magnet with 35 Pound Holding Force and Tri-Voltage Design
Professional Fire Safety Door Control Solution
The LCN SEM7840 is a low-profile recessed wall-mounted door holding magnet from the Sentronic 7800 Series, engineered for fire safety applications. This heavy-duty magnet provides 35 pounds of holding force through tri-voltage design (12V/24V/120V) and releases automatically when fire alarm panels enter alarm condition. UL listed for metal smoke barrier or labeled fire doors and certified under ANSI/BHMA A156.15, the SEM7840 features die-cast housing construction with powder coat finish for long-term durability in commercial applications.
Professional Features & Benefits
- Heavy-Duty Holding Force: Tri-voltage design delivers 35 pounds of holding force for secure door positioning in fire safety applications.
- Fail-Safe Operation: Magnet holds door until electrical current is interrupted, then releases automatically to allow manual door operation during alarm conditions.
- Tri-Voltage Compatibility: 12V/24V/120V operation provides flexible power supply options for various system requirements.
- Low-Profile Recessed Design: Wall-recessed mounting with 6-3/4" projection provides clean installation appearance while maintaining full functionality for pocket door applications.
- Die-Cast Housing Construction: Heavy-duty die-cast housing with powder coat finish ensures long-term durability in demanding commercial environments.
- Fire Safety Compliance: UL listed for metal smoke barrier or labeled fire doors and meets ANSI/BHMA A156.15 standards for code compliance.
- Versatile Installation Options: Suitable for pocket door installations with wood and machine screw pack fasteners included, armature extensions available.
- Manufacturer Warranty: Protected by 2-year warranty for added confidence and protection.
Technical Specifications
- ADA Compliant: Yes
- BAA Qualified: Yes
- Commercial/Residential: Commercial
- Department: Door Hardware
- Door Type: Interior Door
- Electronic: Yes
- Finish Type: Powder Coat
- Mounting Detail: Surface - Magnet
- Mounting Method: Wall Mount
- Product Category: Door Controls
- Product Group: Door Controls
- Product Model: SEM7840
- Product Projection: 6-3/4"
- Product Subgroup: Electromagnetic Door Holder / Releases
- Product Type: Door Magnets
- Product Voltage: 12V/24V/120V
- Series: SEM 7800 Series
- Subcategory: Fire and Life Safety Closers
- Warranty: 2 Year
Professional Applications
- Commercial Building Fire Safety Systems
- Healthcare Facility Fire Door Control
- Educational Institution Safety Compliance
- Industrial Facility Fire Protection
- Multi-Tenant Residential Fire Safety
- Government Building Code Compliance
- Hospitality Fire Safety Systems
Why Choose LCN Quality?
LCN SEM7840 door holding magnets deliver professional-grade reliability with die-cast housing construction and UL listing for fire safety applications. Protected by a 2-year warranty and certified under ANSI/BHMA A156.15 standards for code compliance. Engineered for demanding commercial fire safety applications where dependable automatic release performance is essential.
Manufacturer Resources
LCN Full Line Catalog
Product Specs
- Series:
- SEM 7800 Series
- ADA Compliant:
- Yes
- Mounting Detail:
- Surface - Magnet
- Warranty:
- 2 Year
- BAA Qualified:
- Yes
- Subcategory:
- Fire and Life Safety Closers
- Product Group:
- Door Controls
- Product Subgroup:
- Electromagnetic Door Holder / Releases
- Product Type:
- Door Magnets
- Door Type:
- Interior Door
- Finish Type:
- Powder Coat
- Commercial/Residential:
- Commercial
- Electronic:
- Yes
- Tags:
- lcn sem7840, sem7840
- Product Model:
- SEM7840
- Product Voltage:
- 12V/24V/120V
- Mounting Method:
- Wall Mount
- Product Projection:
- 6-3/4"
- Product Category:
- Door Controls
- Department:
- Door Hardware
LCN SEM7840-689 – Frequently Asked Questions
1) How does the LCN SEM7840 door holding magnet release the door when the fire alarm goes off?
The SEM7840 is a fail-safe electromagnetic holder: it holds the door open while it is energized, and the instant the fire alarm panel drops current to it, the magnet lets go and the door is free to close or be moved by hand. That means the wiring has to be on a circuit the panel interrupts on alarm, not on unswitched building power. It's UL listed for use on metal smoke barrier or labeled fire doors and certified to ANSI/BHMA A156.15.
2) What voltage do I need to run an LCN SEM7840 holding magnet?
It's a tri-voltage unit, 12V/24V/120V, so the same part works off a 12 or 24 volt DC panel output or straight off 120 volt line power. On a job where some openings are fed from the fire alarm panel's low-voltage bus and others are on a 120V circuit, you order one model for all of them instead of splitting the buy by voltage.
3) How does the SEM7840 magnet mount, and how far does it stick out from the wall?
Wall mount, recessed into the wall, with the magnet portion surface at the door. Projection is 6-3/4 inches. The low-profile recessed body is what makes it workable in pocket door applications and in corridors where a floor-standing holder would be in the traffic path.
4) Is an electromagnetic door holder like the SEM7840 the same thing as a closer with a hold-open arm?
No, and the difference matters on a fire rated opening. A closer with a mechanical hold-open arm keeps the door open until someone pushes it closed; it doesn't know the alarm went off. The SEM7840 is a separate electromagnetic holder wired to the fire alarm panel, so the door drops on alarm without anyone touching it, which is what a smoke barrier or labeled fire door opening needs. You still need a closer on the door to actually close it once the magnet lets go, so the magnet is an addition to the closer, not a replacement for it.
5) Will 35 pounds of holding force be enough to hold my fire door open?
The SEM7840 delivers 35 pounds of holding force at the armature, which is the heavy-duty end of the Sentronic 7800 Series range and is meant for commercial interior fire and smoke doors. The force is what resists the closer's spring plus any stack pressure in the corridor, so match it against the closer size on the opening. It's a commercial-rated device, not a light residential holder.
6) What fasteners come with the LCN SEM7840, and what do I still have to order?
Wood and machine screw packs ship with the magnet, so you're covered for a wood stud or a tapped metal substrate out of the box. What isn't included is the power supply or the fire alarm panel connection. If the gap between the wall and the door in the held-open position is more than the standard armature can span, armature extensions are available and are ordered separately.
7) Can I use a door holding magnet on an exterior door, or is it interior only?
Interior door applications. The SEM7840 is built for corridor smoke barrier and labeled fire door openings inside the building, with a die-cast housing and powder coat finish for commercial interior service. For an exterior opening you want a hold-open device rated for outdoor exposure instead.
8) Does the LCN SEM7840 qualify for a federal or state job with domestic sourcing requirements?
It's BAA qualified and ADA compliant, which is what a government or institutional spec typically calls out on a door holder line item, along with the ANSI/BHMA A156.15 certification and the UL listing for metal smoke barrier or labeled fire doors.
9) What finishes does the LCN SEM7840 holding magnet come in?
Two: 689 aluminum and 695 dark bronze, both powder coat. For a facility standardizing corridors, 689 is the match for aluminum frames and most existing LCN closers, 695 for dark bronze openings.
How fast can I get the LCN SEM7840-689 delivered?
Most orders ship the same day from our distribution partners, with quick delivery throughout the
continental
U.S.
Need it urgently? Contact Us for expedited shipping options.
Can I return it if it doesn’t work for me?
Yes—ZenSupply offers a hassle-free return policy. If the product isn’t the right fit,
reach out to our support team for a return authorization or setup a return by following our return instructions.
Does the LCN SEM7840-689 come with a warranty?
Absolutely. The LCN SEM7840-689 is backed by a manufacturer’s warranty.
For full warranty terms, check the product documentation or Contact Us.
How do I get technical support or installation help for the LCN SEM7840-689?
You can call, text, or email our expert support team for fast answers. We’re here to help with
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selection,
installation tips, and troubleshooting. Contact Us
Why buy the LCN SEM7840-689 from ZenSupply?
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