The controller cable that comes with the AUOTERM heaters is 1.5m long as standard.  If you need extra cable so you can mount the controller further away from the heater you will need this option.  
 
The extension cables come in two lengths, 2.6m so total length would be 4m or 7m so total length would be 9m. 
 
IMPORTANT INFORMATION
 
The 2.6m extension cable is only suitable for internal use. 
 
Wiring can be connected with following control wires: 
 
PU-5
PU-20 (12V & 24V)
PU-22
PU-27
 Wiring can be connected with following modems: 
 
Modem QStart
Modem Simcom