With the RS485 relay modules AD-KAB 40 GT and AD-KAB 80 GT, 4 or 8 potential-free NO contacts can be controlled from a distance via RS485 bus. The used Modbus-RTU protocol on these devices on the RS485 bus is an open standard and therefore extremely flexible. The up to eight relays can be individually controlled via a separate Modbus register. The devices are equipped with two rotary coding switches, which can be used to set the bus address on the device. If the DIP switch is active (in manual operation) bus commands for the respective relay are ignored because the manual operation has priority. Due to the compact and efficient switching power supply, the devices can be operated in a wide supply voltage range.



Remote control of loads such as valves or motors in building automation as well as in automation technology.
Attention: A mixed wiring of the relays of extra low voltage and grid voltage is only permitted to a limited extent. For example, care must be taken that relays with 24 V and 230 V signals are not adjacent.

Specific characteristics

  • RS485-Bus
  • Modbus-RTU protocol
  • rotary coding switch for setting the bus address
  • DIP switch for manual relay operation
  • 4 or 8 potential free relays
  • wide range power supply

Business data

Order number
AD-KAB 40 GT RS485 Relaismodul mit 4 Relais
AD-KAB 80 GT RS485 Relaismodul mit 8 Relais
USB/RS485 converter AD-VarioPass3
Customs tariff number / country of origin 8543 70 90 / Deutschland


Data sheet pdf en-kab40_80gt.pdf (266 kB)
Safety instructions pdf ad-safety-instructions.pdf (43 kB)

Technical specifications

Software protocol Modbus-RTU
Data format (default setting) 19200, e, 8, 1
Max. bus users 99
Bus termination 120 ohms both sides at the end
Max. length of bus 500 m (no spur lines)
Cable Twisted and shielded
Maximum switching load AC 250 V, 2 A
Maximum switching load DC 50 V, 2 A
Contact construction Closing contact
Switching operations mechanical 10000000
At 230V/2A AC, cos(phi)=1 600000
At 230V/2A AC, cos(phi)=0,4 200000
At 24V/1 A DC 200000
Voltage range AC 50 ... 253 V AC, 50/60 Hz
Nominal voltage AC 230 V AC
Voltage range DC 22 ... 253 V DC
Nominal voltage DC 24 V DC
Power consumption AC / DC 3,5 VA / 2,5 W
Transmission behaviour
Response time Max. 5 ms
Dimensions (WxHxD) 71x90x58 mm
Type of protection IP 20
Connection method Detachable terminal clamp
Terminals, wire cross section 2,5 mm² flex wire / 4 mm² one wire
Bolting torque terminals 0,5 Nm
Weight ~ 200 g
Manner of fastening 35 mm DIN rail 35mm
Environmental conditions
Ambient temperature -10 ... 60 °C
Storage and transport -10 ... 70 °C (no condensation)
Product family standard EN 61326-1 1)
Emitted interference EN 55011, CISPR11 Cl. B, Gr. 1
Electrical safety requirements
Product family standard EN 61010-1
Overvoltage category II
Pollution degree 2
Galvanic isolation, test voltages
Power supply / RS485-Bus 3 kV, 50 Hz (1 min.)
Power supply / relay output 3 kV, 50 Hz (1 min.)
Relay output / RS485-Bus 3 kV, 50 Hz (1 min.)
Protection circuits
RS485-Bus Electrical surge protection
Power supply Electrical surge and reverse current protection
1) During checking, slight signal deviations are possible.

Block and wiring diagram




CAD / CAE Daten

CAD model is not yet available for this product.

The CAD product overview can be found at:

Modbus communication

data rate: 19200 Baud (Bits/s) parity: even data bits: 8 stop bits: 1

The bus address is set at the front-mounted rotary coding switches. Address 0 is not allowed for bus operation. However, at this zero position the device can always be reached via the standard data format (19200, e, 8.1). Position 0 thus represents a service position, which can be used with incorrect parameterization.

The AD-KAB 40/80 GT supports two Modbus functions. These are the functions "Read Holding Registers" (0x03) and "Write Multiple Registers" (0x10) . The function "Read Holding Registers" data can be read from the device and data is written with "Write Multiple Registers". The individual register width is 16 bits.
Please refer to the Modbus specification for a detailed description of the Modbus communication. This is freely available online, but can also be obtained from the Adamczewski homepage.

The following Modbus data are accessible via the RS485 bus:
Each relay can be read or written (0 or 1) via its assigned register (DOUT_RELAIS_x). But it is also possible to manipulate or read out all relays with the register DOUT_RELAIS_COMPLETE. For AD-KAB 80 GT corresponds bit 0 of the word to relay 1 and bit 7 to the relay 8. With the AD-KAB 40 GT corresponding to relay 4.

start address register number name unit data type read write

relay control:
40501 1 DOUT_RELAY_1 3 1 1
40502 1 DOUT_RELAY_2 3 1 1
40503 1 DOUT_RELAY_3 3 1 1
40504 1 DOUT_RELAY_4 3 1 1
40505 1 DOUT_RELAY_5 3 1 1
40506 1 DOUT_RELAY_6 3 1 1
40507 1 DOUT_RELAY_7 3 1 1
40508 1 DOUT_RELAY_8 3 1 1
41001 1 LIST_RS485_BAUDRATE 3 1 1
41002 1 LIST_RS485_PARITY 3 1 1
41003 1 LIST_RS485_STOPBIT 3 1 1

legend of the data types:
U08: 1 S08: 2 U16: 3 S16: 4 U32: 5 S32: 6 float: 7

coding of the list parameters (list index:value):
baudrate 0:2400 1:4800 2:9600 3:14k4 4:19k2 5:28k8 6:38k4 7:57k6 8:76k8 9:115k2
stop bit 0:1 1:2
parity 0:even 1:odd 2:none

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