JohdotaA small control current in the contactor coil closes the main contacts, which carry the load current, for example of a motor or an electric heater.
Connections
- Main contacts. The supply comes in at the top to terminals 1/L1, 3/L2 and 5/L3, and the load is connected at the bottom to terminals 2/T1, 4/T2 and 6/T3.
- Coil A1–A2. When the coil is energised, the contactor pulls in and the main contacts close. The coil terminals are often both on the top edge of the device. The coil voltage is marked on the device, and on a DC coil A1 is positive.
- Auxiliary contacts. Small contacts for the control circuit, for example for self-holding or a running light. More can be added with separate auxiliary contact blocks.
What the numbers mean
The first digit of an auxiliary contact is its sequence number, and the second digit gives its type: 3–4 is NO and 1–2 is NC. For example, 13–14 is the first contact and NO, and 21–22 is the second contact and NC.
Contactor or relay
The operating principle is the same. A contactor's main contacts, however, are built to withstand the starting current of a motor and to break the load current. An auxiliary relay is meant for control currents.
Remember
- A contactor does not protect the motor. It needs a motor protection circuit breaker upstream, or a switch-fuse upstream and a thermal overload relay below it.
- For motor duty, a contactor is chosen by its power or current rating in utilisation category AC-3.
In your region
Showing notes for
United States, Canada
A contactor together with an overload relay is called a motor starter. On ladder diagrams its coil is usually marked M, and its contacts carry the same letter.
NEMA-rated starters come in sizes 00 to 9, rated by horsepower. For example, a size 1 starter is rated 27 A, or 10 hp at 460 V. IEC contactors have no sizes. They are rated by utilisation category, such as AC-3.
The starter coil is drawn as a circle, like a relay coil: only the letters tell them apart. In the main circuit each starter contact is a pair of short lines.
Source: Siemens: Basics of Control Components, part 1 (STEP 2000 course) · Siemens: Basics of Control Components, part 2 (STEP 2000 course) · Siemens: Basics of Control Components, part 3 (STEP 2000 course) · Square D (Schneider Electric): Wiring Diagram Book 0140CT9201, symbols and examples · Evolution Motion: JIC standard graphic symbols for electrical ladder diagrams
UK & Ireland, Europe, Australia & New Zealand, Other IEC countries
No regional notes on this page yet. If something is different in your country, please send feedback.
Frequently asked questions
How do you wire a contactor?
The supply goes to 1/L1, 3/L2 and 5/L3, and the load to 2/T1, 4/T2 and 6/T3. The coil A1–A2 gets the control voltage through the control circuit, for example the start and stop buttons and the holding contact.
What is the difference between a contactor and a relay?
The principle is the same. A contactor's main contacts are built to withstand the starting current of a motor and break the load current. An auxiliary relay is for control currents.
Why is my contactor not pulling in?
The coil gets no voltage or the wrong voltage. Check the contacts in series, such as the stop button, 95–96 of the overload relay and the motor protection auxiliary contact. Compare the control voltage with the coil rating. On a DC coil, A1 is +.
What do the auxiliary contact numbers on a contactor mean?
The first digit is the sequence number, the second the type: 3–4 is NO and 1–2 is NC. So 13–14 is the first contact, NO, and 21–22 the second, NC.
What does AC-3 mean on a contactor?
The utilisation category for starting and switching off squirrel-cage motors. For motor duty, a contactor is chosen by its AC-3 power or current.
Sources
- Sprecher + Schuh: auxiliary contact terminal markings 13–14 and 21–22
- Schneider Electric FAQ: DC coils of TeSys contactors, positive on A1
- Siemens: Basics of Control Components, part 1 (STEP 2000 course)
- Siemens: Basics of Control Components, part 2 (STEP 2000 course)
- Siemens: Basics of Control Components, part 3 (STEP 2000 course)
- Square D (Schneider Electric): Wiring Diagram Book 0140CT9201, symbols and examples
- Evolution Motion: JIC standard graphic symbols for electrical ladder diagrams