ELECTRICAL BASICS · DRILL 4 OF 5
Contactor wiringA1 A2, auxiliary contacts and terminal numbers.
Tap the right terminal on a real contactor and overload relay: the coil, power in and out, the seal-in contact, the lamps and the overload trip. Nine quick steps.
Every motor starter has a contactor: a heavy-duty switch that a small 24 V coil pulls in. The terminal numbers printed on it tell you exactly what each screw is for, so once you can read them, every starter diagram makes sense.
Tap your answers on the contactor below. If you miss one, you’ll see why and can try again.
Contactor terminal numbers
| Terminal | What it is | Wired to |
|---|---|---|
| A1, A2 | The coil | A1: the switched control voltage (through Stop, Start and the overload’s 95–96). A2: 0 V, the common |
| L1, L2, L3 (1, 3, 5) | Main contacts, line side | Power in, from the disconnect or breaker |
| T1, T2, T3 (2, 4, 6) | Main contacts, load side | The overload relay, then the motor |
| 13–14 | Auxiliary contact, normally open | The seal-in (in parallel with Start), a RUN lamp, a PLC input |
| 21–22 | Auxiliary contact, normally closed | A STOPPED lamp, or the other contactor’s coil on a reversing starter |
Reading the two digits
- The second digit is the function: 1–2 normally closed, 3–4 normally open.
- The first digit is the position: contact 1, contact 2, and so on. So 13–14 is contact 1 (NO) and 21–22 is contact 2 (NC).
The overload relay
- 95–96 is normally closed. It goes in series with the coil, so a trip drops the contactor out.
- 97–98 is normally open. It closes on a trip, for a TRIPPED lamp or a PLC input.
Always check the wiring diagram and the label on the actual device. Coil voltages vary (24 V DC, 120 V AC and more), and the coil voltage is printed on the coil.
Common questions
What are A1 and A2 on a contactor?
They’re the two ends of the coil. The switched control voltage goes to A1 and A2 goes to the common (0 V or neutral). When the coil gets its rated voltage, it pulls the contactor in and closes the main contacts.
What do 13-14 and 21-22 mean on a contactor?
They’re auxiliary contacts. The second digit gives the function: 3–4 is normally open and 1–2 is normally closed. 13–14 is a normally open contact, often used for the seal-in; 21–22 is normally closed.
What are L1 L2 L3 and T1 T2 T3?
L1–L3 are the line side, where power comes in. T1–T3 are the load side, out to the overload relay and the motor. Some contactors mark them 1, 3, 5 and 2, 4, 6.
What are 95 96 97 98 on an overload relay?
95–96 is the normally closed trip contact, wired in series with the contactor coil so a trip stops the motor. 97–98 is normally open and closes on a trip, for a tripped lamp or a PLC input.
Why does my contactor drop out when I release Start?
The seal-in (holding) contact is missing or loose. A normally open auxiliary contact, usually 13–14, has to be wired in parallel with Start so the coil stays fed after the button is released.
YOUR NEXT STEP
Try it on a real panel
Level 1 puts you at a motor starter panel: lock it out, prove zero energy with the meter, wire the control circuit and run the motor. It's free.
Training practice only. Always follow your site's written energy control procedure, your employer's authorization rules and the meter maker's instructions on real equipment.