PlantFlow 3D › Guides › Contactor terminals explained: 1-2, 3-4, 5-6, A1-A2, 13-14 and 21-22
Contactor terminals explained: 1-2, 3-4, 5-6, A1-A2, 13-14 and 21-22
How to read contactor terminal numbers, which contacts carry motor current, how the coil is connected, and how auxiliary contacts are used for hold-in and interlocks.
Main contacts: 1-2, 3-4, 5-6
A three-pole contactor has three main contacts that carry the motor current. The supply side is marked 1, 3 and 5 (sometimes L1, L2, L3) and the load side 2, 4 and 6 (T1, T2, T3). The odd number is always the incoming side.
Size the contactor for the motor power and duty, not just the current: starting and stopping often (inching, plugging) needs a larger contactor.
The coil: A1-A2
The coil terminals are A1 and A2. The coil voltage is printed on the contactor, for example 230 V AC or 24 V DC. Connecting a 24 V coil to 230 V burns it in seconds; a 230 V coil on 24 V will not pull in.
The control circuit (buttons, overload contact, PLC output) switches the line to A1, and A2 normally goes to neutral or 0 V.
Auxiliary contacts: 13-14 and 21-22
Auxiliary contacts are numbered with two digits. The second digit tells the type: 3-4 is normally open, 1-2 is normally closed. The first digit is the position number. So 13-14 is the first NO contact and 21-22 the second, an NC contact.
13-14 is typically wired across the START button as the hold-in (seal-in) contact. NC auxiliaries such as 21-22 are used for electrical interlocks, for example in forward-reverse and star-delta starters, so two contactors can never close together.
Try it yourself
Open the 2D diagram and tap KM1 to see every terminal. In the Wiring tab the step-by-step player shows which wire lands on each terminal.
Open the PlantFlow 3D simulator →Safety: this guide explains principles for learning. Real installations must follow the applicable codes, the equipment manufacturer's instructions and the approval of a competent, qualified person. Isolate, lock off and prove dead before touching any circuit.