hello, I am having a little trouble understanding how this works:

my attached (appalling sketch) is of a circuit protection circuit to prevent incorrect polarities of power source being connected to a load.
There is a fuse which is then connected both to the load and to a diode.

Can someone please outline to me how this actually functions.

Thanks kindly for any help.

 

When the power supply is connected correctly, the diode is reverse biased. No current will flow through it. If the power supply is connected backwards, the diode will be forward biased. This will cause current to flow through the diode, bypassing the load. This creates a short circuit, drawing maximum current and blowing the fuse. The fuse is there to protect the power supply from damage.

Keep in mind the diode and fuse must be chosen based on the voltage, current, and type of load