Offgrid Battery Isolator "Loopback" Wiring - What is it and why do you need it?
The reason for this, is to provide a "readily available" fuse and isolation device all in one, which will disconnect the batteries AND the solar regulator/charger from the DC Bus and the Inverter.
If we only isolate the Positive and Negative of the battery, when we throw the emergency switch the batteries will be cut off from the inverter, but the DC bus will still be supplied by the solar regulator if there is power available from the PV array. The inverter will still be able to produce lethal AC voltage.
If our disconnection swith has 3 or more poles, we can also switch out the positive of the solar regulator at the same time, ensuring there is no power from the PV array on the DC BUS or to the Inverter.
The usual practice is to wire the positive of the solar regulaor through the bottom of the 3rd isolator pole and then link it at the top to the positive pole of the breaker:
You can buy these components here: