LV Handbook › Tools › Relay Sandbox

Relay Sandbox

Wire a relay to locks, buzzers and door inputs and watch the current flow, or test how a door behaves on card reads, REX, forced and held doors, fire alarm and power loss.

Wiring board

Tap a terminal, then tap another to run a wire. Tap a wire to remove it. Red dashes are the supply side, blue dashes are the return.

Examples:

Fault-finding

Load a broken install, find the fault on the board, fix it, then check your work.

Pick a scenario and load it.

Parts

Result

Checks

    Electrical checks

    Drop = 2 × length × ohms per foot × lock current, the same math as Cable & Voltage Drop. Supply draw is the peak with the relay at rest or energized.

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    How the relay works

    COM is the moving contact. With the coil off, COM touches NC (normally closed). When the coil is energized, COM moves to NO (normally open). Access controllers energize the lock relay to unlock.

    A dry contact trigger is just a switch: you supply the coil voltage through it. A voltage output sends its own voltage, so it wires straight to the coil.

    Fail-safe locks (mag locks) need power to stay locked, so they go on NC. Fail-secure strikes need power to unlock, so they go on NO.

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