Link to Crowbar Circuit Part 1 which has the circuit diagram and part list.

The last part of the project was to mount the circuit in the enclosure, I also bought a panel mounted digital voltmeter which is really useful.

Internal views of the unit, I have modified the board from that shown in Part 1 by the addition of a fuse holder mounted on the veroboard, this has a 2A slow blow fitted and protects the non terminal post outlets.