more than 12 channels

[dan]

It depends on the relay board design but there is usually a jumper between VCC and JD-VCC. The jumper gets removed and the power from the external power supply connects to GND (negative from the PS) and JD-VCC (positive from PS) The +5V line from the pi connects to VCC on the relay board, the GND from the Pi is NOT connected. This is for a low level trigger relay board.

I have tested this with a SainSmart low-level trigger (active low) 8 channel relay board and it works as expected with the Active-low relay option checked in SIP's Options > Station handling