A magnetic door lock holds a door closed with an electromagnet and an armature plate. Remove the power and it releases immediately — which is exactly why it suits escape routes. Choose the holding force to match the door and frame, not to chase the biggest figure on the box.
The most common thing we correct at the counter isn't the lock. It's someone buying 500 kg of holding force for a hollow internal frame that will tear out at a fraction of it.
1. How a maglock actually works
Two parts. The lock body mounts on the frame and contains the electromagnet. The armature plate mounts on the door leaf. Energise the coil and the two bond together.
That's the whole mechanism, and it has one consequence worth understanding: there are no moving parts and nothing to jam. It also means the lock is fail-safe by nature — no power, no hold, door opens. You cannot make a maglock fail-secure, and you shouldn't try.
2. Holding force — and why bigger is not better
Holding force is quoted in pounds or kilograms: the straight pull needed to separate the armature from the energised lock.
Here's the part the spec sheet doesn't tell you. The lock is almost never the weakest thing in the assembly. The chain is: armature fixings → door leaf → frame → frame fixings → wall. A 280 kg lock bolted to a timber frame that pulls out at 120 kg gives you a 120 kg door.
So the sensible order is: assess the frame, then buy the lock that suits it.
- Internal timber and glazed office doors: a slimline 600 lb (280 kg) unit is usually right.
- External, high-traffic or higher-risk doors: step up — and check the frame can carry it before you do.
Trade Tip: Before you order, put a hand on the frame and give it a firm pull at the head where the lock will sit. If it flexes, more holding force is money thrown away. Fix the frame or accept the lower figure. We have seen a 500 kg lock still perfectly bonded to an armature that had taken a strip of door with it.
3. Monitored or unmonitored
A monitored lock reports its own state — bonded or not bonded — back to the system. An unmonitored one just draws current and hopes.
The difference shows up in ordinary life, not in dramatic break-ins: a door propped on a mat, a leaf that has dropped on its hinges and no longer makes full contact, a lock energised against an armature that is 4 mm away and holding nothing. Without monitoring nobody finds out until something is missing.
The RGL ML600-M is a monitored slimline maglock rated 600 lb (280 kg), running 12/24 V. For a pair of doors, the ML600-D-M is the double monitored version at 2 × 600 lb in one housing — neater and cheaper than two singles, and it keeps the cabling to one run.
Our position: buy monitored, even when the specification doesn't ask for it. The uplift is small and the first quiet failure pays for it.
4. The air gap, and the thing that ruins performance
A maglock develops its rated force when the armature sits flat against the lock face with a minimal, even gap. Magnetic attraction falls away fast with distance, so a few millimetres of misalignment costs a surprising amount of holding force.
What causes it, in the order we see it:
- Armature bolted rigid instead of allowed the slight float it is designed to have.
- A door that has dropped, so the plate meets the lock at an angle.
- A warped leaf — common on external doors after a wet winter.
- Paint. Several coats on the armature face is an air gap you painted on yourself.
Trade Tip: If a door starts rattling or you can pull it open with a decent shove, don't order a bigger lock. Check the gap and the alignment first. Nine times out of ten you have a hinge or a bracket problem, and a bigger lock will behave exactly the same way.
5. Brackets: the part people forget to order
A lock and armature bolt straight onto an outward-opening door with a decent frame head. Anything else needs a bracket.
- Z and L brackets — for inward-opening doors. The Z carries the armature down and back; the L supports it. This is the single most-forgotten line on a maglock order.
- Surface armature housings — where the armature cannot be recessed, or on glass and frameless leaves.
We stock a Z+L bracket for 500 kg locks in satin-anodised aluminium, and the CDVI AMA3 surface armature housing for 300 kg locks in aluminium, 188 × 54.5 × 15 mm.
6. Escape routes — the non-negotiable bit
If the door forms part of a means of escape, the lock is only one third of the job. You also need:
- An interface to the fire alarm so the lock drops when the alarm activates. In the UK, actuation of release mechanisms on escape-route doors is covered by BS 7273-4, applied according to the building.
- A manual emergency door release at the door, operable without a card, code or key — a resettable illuminated unit rather than a break-glass you have to keep spares for.
This is competent-person design work, not a shopping decision. We will supply every part and check compatibility with you; we won't pretend the fire interface is something to work out on site.
Summary: choosing a magnetic door lock
| Decision | Answer |
|---|---|
| Failure mode | Fail-safe, inherently — releases on power loss |
| Holding force | Matched to frame strength, never maximised |
| Single or double | Double unit for door pairs — one housing, one cable run |
| Monitoring | Monitored, even when not specified |
| Air gap | Flat, even, minimal. Check before upsizing anything |
| Bracket | Z+L for inward-opening; surface housing where no recess |
| Escape route | Fire-alarm interface (BS 7273-4) + manual release. Competent person |
Expert Help in the West Midlands
Villa Road, Birmingham, since 1975. Bring photographs of the leaf, the frame and which way the door swings — that's all we need to tell you the lock, the bracket and whether the frame will actually hold it. It takes two minutes at the counter and saves a second trip for a bracket nobody ordered.
Browse access control systems, including exit buttons and door releases.
Frequently asked questions
Do magnetic door locks work in a power cut?
No — and that is by design. A maglock is fail-safe, so losing power releases the door. If you need the door to stay locked without power you need a fail-secure lock instead, and that is not appropriate on an escape route.
What holding force do I need for a magnetic door lock?
Enough for the door, no more. A 600 lb (280 kg) slimline unit suits most internal timber and glazed doors. Beyond the point the frame can carry, extra force buys nothing because the frame gives way first.
Why does my magnetic lock keep letting the door open?
Almost always the air gap or alignment, not the lock. Check the armature sits flat with minimal even clearance, that the door has not dropped on its hinges, and that the armature face has not been painted over.