By adding the controller, every reader and every lock at its worst case, then allowing margin for inrush and for future doors.

The controller's own consumption is small. Readers add up, particularly illuminated keypads, displays and biometric units.

Locks dominate. A magnetic lock draws continuously while holding the door; an electric strike draws only during the release. A panel of maglocks needs a much larger supply and battery than the same number of strikes.

Inrush matters when several locks operate together - a fire alarm release, for instance - and a supply sized only for steady state may not manage it.

Cable voltage drop reduces what actually arrives at the device, and long runs need either heavier cable or a local supply.

Size for the doors the panel will eventually serve, not only the ones being commissioned now.

As long as the local standard, the insurer or the site's risk assessment requires - and the battery should be sized at end-of-life capacity, not when new.

Required standby duration varies by territory and by the grade of system, so it is a local answer rather than a universal figure.

Batteries lose capacity as they age. Sizing on the nominal rating means the system falls short of its duration well before the battery is replaced.

The load during an outage includes the locks. Fail-safe magnetic locks continue drawing current the whole time, which is often the dominant term.

A supply that monitors and reports battery condition turns a silent failure into a fault message.

Record the installation date inside the enclosure and put replacement on a planned cycle. Reactive replacement means discovering the failure during the outage.

Inside the area it protects - a plant room, riser or locked cupboard - never in a public corridor or an unsecured lobby.

Opening a panel exposes the lock output terminals. Anyone who reaches them can operate the door without any credential.

That makes location a security control rather than a convenience, and it is one of the commonest weaknesses found in surveys of existing installations.

A monitored tamper switch reports opening, but only if the input is supervised and somebody responds to the alarm.

Where a panel must sit in a semi-public place, use a locked enclosure, conceal the cable entries, and consider moving the decision to a controller inside the door frame instead.

Consider maintenance access too. A panel above a ceiling or behind stored goods will be worked on badly, and its battery will not be changed.

Larger than the calculation suggests - the cost difference is small and the benefit lasts the life of the installation.

A cramped enclosure produces bad terminations, cables forced into tight bends, and a battery wedged against a board.

Room to work matters every time someone opens it, which over twenty years is many times.

Allow space for the battery specified, not the smallest one that fits, and for the expansion board that will be added when a door is retrofitted.

Cable entry and containment need planning at first fix. Twenty cables entering through one gland plate is a mess that never gets tidier.

Check the ingress rating against the location. A riser is not a plant room, and a plant room is not outdoors.

Every door, every cable at both ends, the battery installation date, and the panel's identity in the management software.

The next person to open the enclosure will not be the one who installed it, and quite possibly not from the same company.

Door numbers on the terminal blocks should match the numbers used in the software and on the drawings. Three different numbering schemes is the normal starting position and it wastes hours on every fault.

Cables identified at both ends can be reused. Unmarked cables get replaced.

Write the battery date inside the lid. It is the only reliable record of when it is due.

Keep a copy of the as-built inside the panel. It survives staff and contractor changes better than any document system.

Yes, and the alarm has to go somewhere that produces a response - otherwise it is a switch that does nothing.

A tamper switch signals when the door of the enclosure is opened, and on better enclosures also when it is removed from the wall.

The value is entirely in the response. A tamper alarm logged and never reviewed adds no security.

Tampers should be reported out of hours to whoever monitors the intruder system, because that is when an unexpected panel opening matters.

Maintenance visits will generate them, so there needs to be a way to log planned work and distinguish it from the unexpected.

Supervised tamper circuits, which detect a shorted or cut wire as well as an open switch, defeat the obvious bypass and cost nothing extra to wire.

They can, and on small systems they usually do - but separating them avoids a class of intermittent fault that is very hard to diagnose.

Locks are electrically noisy. Magnetic locks and strikes generate transients when they release, and those transients can reset a controller sharing the same supply.

Suppression across the lock is the minimum precaution and should always be fitted.

A separate supply or a separately fused and filtered rail for locks removes the interaction entirely and is standard practice on larger panels.

It also isolates faults: a shorted lock cable then takes out one door rather than the controller and every door with it.

Individually fusing each lock output is cheap and turns a whole-panel failure into a single-door one.