How to Wire an EM Lock With an Access Control Reader and Exit Switch

Short answer: an EM lock is wired so that the reader cuts its power to open the door. Run +12 V from the power supply to the reader's COM terminal, take the lock's positive wire from the reader's NC terminal, and return the lock's negative wire to GND. The exit switch goes between the reader's OPEN (or PUSH) terminal and GND, using the switch's COM and NO contacts, so pressing it releases the door for the same timed period as a valid card.

This guide covers the wiring only, in plain steps an electrician can follow. For fixing the lock on the door, brackets and testing, use our full access control installation manual.

What parts are in a standard EM lock door?

Every single-door system has the same five parts, and they all connect at the reader and the power supply:

• Power supply. Takes 230 V mains and gives 12 V DC to the reader and the lock. Use a proper access control supply such as the PK-80 (12 V 3 A), not a phone-style adapter.
• Reader or keypad. Checks the card, PIN or finger and switches an internal relay. That relay has three terminals: COM (common), NO (normally open) and NC (normally closed).
• EM lock. A magnet on the frame and a steel plate on the door. It holds only while it gets power, which is why it is called fail-safe.
• Exit switch. A push button or no-touch sensor on the inside, so people can always leave without a card.
• Emergency break-glass (for escape routes). Cuts power to the lock directly, even if the reader fails.

What do NO, NC and COM mean?

Think of the relay as a switch with one input and two outputs. COM is the input. When the reader is idle, COM is connected to NC. When a valid card is shown, the relay clicks over for the door-open time and COM connects to NO instead.

• EM lock (fail-safe): wire it to COM and NC. It is powered, and locked, all the time, and loses power only when the relay clicks.
• Drop bolt or electric strike that is fail-secure: wire it to COM and NO. It gets power only when the relay clicks. Some drop bolts are fail-safe, so check the lock's own manual first. Our EM lock vs drop bolt guide explains the difference.

The exit switch has the same three terminals. Use its COM and NO, so the circuit closes only while the button is pressed.

How to wire an EM lock, reader and exit switch: step by step

Switch off the mains before you start. Mains connections to the power supply should be done by a qualified electrician. Use 4-core or 6-core cable and keep the lock and reader on separate cores.

1. Mains to the power supply. Connect phase, neutral and earth to the supply's AC input terminals. Mount it indoors, away from water, where you can reach it later.
2. Power to the reader. Run +12 V and GND from the supply's DC output to the reader's +12 V and GND terminals. Check polarity twice: reversed polarity is the most common reason a new reader stays dark.
3. +12 V to the relay COM. Run a second +12 V wire from the supply to the reader's COM terminal. This is the power that will feed the lock.
4. NC to the lock positive. Connect the reader's NC terminal to the EM lock's positive (usually red) wire.
5. Lock negative to GND. Connect the lock's negative (usually black) wire back to GND on the supply.
6. Fit a diode. Put a 1N4007 diode across the lock's two wires, with the stripe towards +12 V, unless the lock has one built in. It absorbs the voltage spike the magnet throws back when it switches off, which otherwise can reset the reader.
7. Exit switch. Connect the switch's COM to the reader's GND and the switch's NO to the reader's OPEN (some readers label it PUSH or EXIT).
8. Break-glass on escape doors. Cut the lock's positive wire and pass it through the break-glass unit's normally closed contacts, so pressing it breaks power to the lock no matter what the reader does.
9. Power on and measure. Check 12 V DC at the reader and at the lock terminals with a multimeter. Then set the door-open time on the reader. On the WP-25 keypad, the description lists an adjustable door relay time of 0 to 99 seconds; 3 to 5 seconds suits most doors.

Where do the extra wires on an LED or feedback EM lock go?

Basic EM locks have two wires. Locks with a door-status sensor have extra terminals. The EM-602 description lists an inbuilt relay and monitored door sensor, and the EM-605BT lists an inbuilt door sensor and a 5-point terminal. The two power wires connect exactly as above. The sensor contacts connect to the reader's door-sensor input, if your reader has one, or to an alarm panel zone. If you do not need door-status monitoring, leave them unconnected. See the EM locks with LED, feedback or timer if you want this.

Common wiring mistakes and quick fixes

• Lock does not hold at all: it is on NO instead of NC, or there is no 12 V at the lock. Move it to NC and measure.
• Holds weakly: voltage drop on a long, thin cable. For runs over about 30 metres, use thicker conductors or move the supply closer to the door.
• Reader restarts when the door opens: no diode, or lock and reader sharing one thin core.
• Exit switch does nothing: wired to the switch's NC contact, or to the wrong reader terminal.
• Door opens in a power cut: normal for an EM lock. If that is not acceptable, add battery backup; see our access control power supply guide.

Parts for one EM lock door, with prices

Buying the parts one by one (EM-602, WP-25, PK-80 and a PSW-44) comes to ₹6,566. A matched kit such as Combo-CN57 costs less and arrives with parts that are known to work together. Browse EM locks, readers, exit switches and complete door kits, or pick your door type in the access control kit builder.

FAQ

Should an EM lock be connected to NO or NC?

NC. The lock must be powered while the reader is idle and lose power when a valid card is shown, and that is what the COM and NC contacts do.

How many wires does an EM lock have?

A basic EM lock has two, positive and negative. Locks with LED or door-status feedback have extra terminals for the sensor; the power wiring stays the same.

Can I connect an EM lock directly to a 12 V adapter?

It will hold, but nothing will release it except unplugging. You need a reader, timer or exit switch in the circuit, and an access control power supply is safer than a phone-style adapter.

Why do I need a diode across the EM lock?

When the magnet switches off it creates a reverse voltage spike that can reset or damage the reader. A 1N4007 diode across the lock, stripe to +12 V, absorbs it.

How do I wire the exit button?

Use the button's COM and NO contacts. Connect them between the reader's OPEN (or PUSH) terminal and GND.

Will the EM lock stay locked during a power cut?

No. An EM lock is fail-safe and releases when power goes. Add a battery backup supply if the door must stay locked during cuts.

Prices are NavKar Systems website prices on 27 October 2026, inclusive of GST, and may change.