How to Wire and Test a 5 Pin Relay?

Fuses are there to protect the WIRING.

Most jurisdictions have an applicable electrical standard for fixed installations. In the UK, for example, BS7671 applies.

This thread probably belongs in the electrical engineering section.

i would have to partially disagree with that statement.

While it's correct for circuit wiring, many items of equipment have internal fuses that are intended to protect the components of that device rather than the internal wiring which, in most cases, would easily withstand a current in excess of the capacity of some of the very small fuses often employed.

It would be hard to justify a 10mA fuse in a device as being there for the protection of the wiring.

<...should always run a fuse in between the power source and the relay...> doesn't sound like an <...internal fuse...>.

Of course it does.

Anywhere in the circuit, from the switchboard - or maybe the power station if we want to be really accurate to the relay is between the power source and the relay.