Electric Door Locks: Maglock vs Electric Strike vs Drop Bolt

The lock is the part of an access control job that gets the least attention, and it causes the most callbacks. A great face or fingerprint terminal means little if the lock does not suit the door: it won't hold, it releases at the wrong moment, or it runs hot and weakens within months.

This article covers the three lock types we install most in Egypt, the fail-safe versus fail-secure decision, and a worked power budget.

Magnetic locks: 280 kg or 500 kg

A maglock is an electromagnet fixed to the door header and a steel armature plate fixed to the door leaf. Power on, the two clamp together. Power off, the door is free. With no moving parts, a well-installed maglock lasts for years.

The two common ratings are 280 kg (sold as the 600 lb class) and 500 kg (the 1200 lb class). Our rule of thumb:

• 280 kg: internal office doors, admin rooms, light glass doors.
• 500 kg: main entrances, heavy steel doors, stores, and any door likely to be pushed or tampered with.

Holding force is rated with full face contact and a straight perpendicular pull. Gaps or misalignment cut the real figure sharply, so a sloppily fitted 500 kg lock can hold less than a carefully fitted 280 kg one.

Brackets: L, ZL and U

Outward-opening doors take the lock directly on the frame. Inward-opening doors need a ZL bracket, and frameless glass doors need a U bracket clamped to the glass. One mistake we see often on site surveys: the armature screwed down rigidly. It should rock slightly on its centre bolt so it sits flat against the magnet.

Electric strikes for framed timber and metal doors

An electric strike replaces the keeper in the frame and works with the existing mechanical mortise lock. When access is granted, the keeper releases and the door can be pushed open. From inside, the lever handle always opens the door mechanically.

The door looks completely normal, with nothing bulky on the header. The catch is installation: it needs accurate routing of the frame and precise alignment with the latch. Good for offices, clinics and villas; less suited to glass.

Drop bolts for double-swing glass doors

A drop bolt sits concealed in the header and drives a pin down into a strike on the top edge of the door. It is the usual choice for tempered glass doors that swing both ways.

Alignment is everything. If the hinges or floor spring sag by a few millimetres, the bolt will not drop. Many models include an adjustable relock delay so the door settles first, and some include a door-position sensor. Startup current is higher than holding current, so check the datasheet before choosing the power supply.

Fail-safe or fail-secure

• Fail-safe: the door releases when power is lost. Maglocks are inherently fail-safe, as are most drop bolts.
• Fail-secure: the door stays locked without power and releases when energised. Most office electric strikes ship this way; some are field-switchable.

Wiring to the controller relay

The choice also decides the wiring. A fail-safe lock normally goes on the NC and COM terminals, so it stays powered at rest and the relay cuts power for a few seconds on a valid read. A fail-secure lock goes on NO and COM. Swap them and the door works backwards, a fault we meet more often than you would expect.

Escape-route doors must allow free exit in an emergency, which means fail-safe hardware, an exit button, a break-glass and a fire alarm interface in line with civil defence requirements. Server rooms and sensitive stores may suit fail-secure, as long as there is mechanical egress from inside.

Power and battery: a worked example

Most of these locks run on 12 V DC, some on 24 V as well. A maglock typically draws 300 to 500 mA at 12 V; we use the higher value.

Two doors with 500 kg maglocks, one controller, two readers:

• Locks: 2 × 0.5 = 1.0 A
• Controller: about 0.3 A (check its datasheet)
• Readers: 2 × 0.1 = 0.2 A
• Total 1.5 A; with 25% headroom, 1.875 A

Choose a 12 V 3 A supply, since part of the output charges the battery. With a 12 V 7 Ah battery and roughly 70% usable capacity: 7 × 0.7 ÷ 1.5 ≈ 3.3 hours. An estimate that drops as the battery ages.

Don't power locks over network cable

Cat6 at 23 AWG is about 0.066 Ω per metre. For a lock 30 m away the loop is 60 m, around 4 Ω, so 0.5 A drops about 2 V and the lock sees 10 V. A 0.75 mm² copper pair (about 0.023 Ω/m) drops only about 0.7 V over the same run.

Tip for installers: make sure there is a flyback diode across the lock coil (many locks have one built in). The voltage spike when the coil switches off slowly damages controller relays. A separate supply for locks, apart from the readers and controller, prevents a lot of odd faults.

Accessories that complete the door

You will also need an exit button (no-touch types work well in clinics), an emergency break-glass on escape doors, a door contact so the system knows when a door is held open, and an access control power supply with a fire alarm input. General units are in our power supply range; pick one with battery backup if the lock is fail-safe.

How Do Link helps

Our Bab El Louk showrooms stock locks and accessories in the SIB access control range, plus ZKTeco and Hikvision access control. Our technical team checks the door type and swing direction with you before you buy. We offer wholesale and project pricing, a one-year warranty, and delivery to every governorate in 2 to 3 working days.

Start with the door

Send us a photo of the door, its material and swing direction through our contact page, and we will recommend the lock, bracket and power supply. For the bigger picture, see our access control solutions.

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