To provide secure locking of swinging cell doors using third party security management systems (SMS) or conventional key control.


The 4L78 is a surface mounted lock of robust construction based on the Chubb Lock Custodial Services standard cell lock footprint.
The main bolt is a sprung latch providing a throw of 25mm, secure locking is achieved by two independent methods:

Electrical Mode. Locking/unlocking by 24 Volt DC controlled sequence from an external source (SMS). Bolt withdrawal by handle, which
should also be used when closing the door.

Manual Mode. Locking/unlocking achieved using conventional (mechanical key). Bolt withdrawal by handle, which should also be used
when closing the door. Key operates from corridor side only.

Manual Override. In the event of power or communication failure an override key is used to disable electric locking function.
The lock will operate if slammed to shut, however, CLCS recommend that in normal operation the handle is used to withdraw the bolt when closing.


Solid Case Technology; Lock case machined from single piece carbon steel.
Steel main bolt, with carbide anti-cutting rollers, and 25mm throw.
Unique dual solenoid electric locking latch.
Independent 7-lever locking mechanism.
Factory restricted key section.
Lock provides status monitoring of critical functions and tamper.
5 bolt secure fixing.
Integral baffle arrangements to resist manipulation and interference via the keyhole.


Mechanical locking mechanism tested to a minimum of 100,000 operations.
Handle mechanism tested to a minimum of 300,000 bolt operations.
Solenoid locking unit tested to a minimum of 1,000,000 cycles.
Solenoid arrangement designed to operate at +/-10% of 24V DC regulated supply.
Nominal operating current 500mA.
Saw attack 12 hours.
End load 9KN.
Side Load 13.5KN.

Additional features

Can be configured to provide cell side furniture to be used where remote
release is desirable.
Range of fixings including backplates, stud fixings, locking plate and keeps.
External handle designed to shear under excessive load to prevent damage to internal lock mechanism.
Interchangeable mechanical inner locking unit to enable re-coding.
This lock is not available under a master key system.

Materials and finishes

Lock case - carbon steel electro-plated and powder coated exterior. 
Main bolt - carbon steel electro-plated.
Main bolt follower - high tensile brass.
Keys – Hardened Steel.
Levers and springs – Brass / phosphor Bronze.

Dimensions and Weights

Case Height 286mm
Case Length 267mm
Case Thickness 29mm
Bolt Throw 25mm
Bolt Depth 45mm
Bolt Thickness 22mm

Weight (lock only) 12.4Kg

Total Range

The lock is available in left or right hand variants for opening in or opening out doors and can be fitted to steel or wooden doors. A range of backplate stud lengths is available to suit door thicknesses from 25 to 70mm.

Fully dimensioned customer drawings are available on request to assist with door preparation.