A modular contactor is the DIN rail version of a contactor: the same switching function in a package that clips beside MCBs and RCDs. It takes one to three module widths, closes on a coil signal, and leaves the load circuit switched without anyone standing at the board.
The BCH8 from C&J Electrical covers 16 A to 100 A in one to four poles, declared to IEC/EN 61095. Each pole carries two current ratings, AC-7a and AC-7b, and reading them correctly is most of the selection exercise. This article explains what the two figures mean, how the coil options work, and where the series fits.
What a modular contactor does in a board
In a building, most switching duty is repetitive and modest: lighting floors, heating zones, ventilation fans, small pumps. An AC contactor takes that duty off the manual switch, so a lighting circuit can be controlled from a timer, a sensor or a building management output instead of by hand.
The modular format is what makes it practical in a distribution board. The device occupies the same rail and the same width system as the protective devices, so it sits next to the MCB that protects it, and the panel needs no separate mounting plate or a duct run to a remote contactor.
AC-7a and AC-7b on the same pole
Each BCH8 pole is rated twice. AC-7a is the figure for low-inductance loads: lighting, heating and resistive distribution. AC-7b is the figure for motor loads, and it is lower, because closing into a motor and opening a stalled rotor are harder duties than switching a resistive circuit.
On a 25 A device the two figures are 25 A and 9 A. The same gap repeats across the range, and it is the first thing to check on the datasheet: selecting from the AC-7a column and then connecting a pump is a common mistake in this product family. The contactor will still close. What changes is the contact life behind the number.
The practical rule is to identify the load first and read the column second. For a motor, use the AC-7b figure even where the measured current looks small.
Coil versions and manual operation
The standard coils are 24 V, 110 V and 240 V AC at 50 Hz. Electronic versions extend this to DC 12 V and 24 V, AC/DC 24 V and 36 V, and two wide bands of 18-40 V and 90-260 V, which suit control supplies that are not closely regulated.
Manual versions carry an M in the model code and add a front selector . A circuit can then be latched on or locked off during maintenance and returned to automatic control afterwards, without a separate switch in the panel.
Technical data
| Type | Modular contactor for DIN rail, AC coil |
|---|---|
| Standard | IEC/EN 61095 |
| Poles and modules | 1P, 2P, 3P, 4P; 1 to 3 modules |
| Rated current | AC-7a 16, 20, 25, 32, 40, 63, 100 A; AC-7b 6, 7, 9, 12, 18, 25 A (100 A: AC-7a only) |
| Rated operational voltage Ue | 250 V AC (1P, 2P); 400 V AC (3P, 4P), 50/60 Hz |
| Coil voltage | 24, 110, 240 V AC, 50 Hz |
| Mounting and width | 35 mm DIN rail; 18 mm per module |
Where the BCH8 is used
- Lighting circuits: floor and zone circuits in commercial and public buildings, switched in groups from a timer, sensor or building management system.
- Heating and ventilation: zone valves, fan coils and small air handling units on the AC-7a rating.
- Small pumps and fans: on the AC-7b rating, where the motor current stays inside the reduced figure.
- Boards with DC or wide band control: the electronic coil versions accept 12 V DC up to 260 V AC/DC.
- Retrofit and extension work: where DIN rail space, rather than panel area, is the constraint.
What to confirm before ordering
- Load type first: AC-7a for lighting and heating, AC-7b for motors.
- Poles and module width: 1P takes one module, 2P one or two, 3P two or three, 4P two.
- Coil voltage and control type: AC, DC or AC/DC, and the band the control supply actually delivers.
- Manual override: needed where a circuit has to be held during maintenance.
- Accessories: auxiliary contacts and 3 mm or 9 mm spacing pieces, where status feedback or thermal spacing is required.
About C&J Electrical
Zhejiang C&J Electrical Holding Co., Ltd. manufactures low-voltage electrical products, mainly circuit breakers, contactors and related control products. The company supports OEM brand customization and can ship products as SKD kits for local assembly.
For more information on the BCH8 or to request a quotation, please contact us.
Post time: Nov-11-2026