I was involved in the initial stages of adding mobile phone small cells (PICO) to this style of phone box, the KX100 and KX100+.
All of the original boxes were supplied as a TT with no earth, as all the items were class 2 there was no requirement for an earth.
As the kit we were installing was class 1 BT went round and added an earth electrode, normally a rod installed behind the power panel. They also added SMART RCD and 6 amp MCB for us to terminate into.
Have you carried out a Ze on the supply to see if you're getting a good earth through the cabinet root?
This was mounted onto a DIN rail on the ply sheet behind the power panel.
Some had main switches and some didn't but you might be able to get away with using the existing fuse carrier for the light to provide an isolation point for you to install the supply for the defib unit.
On another project we did install a DIN rail in the cab with RCD and fuse carrier etc with a Perspex cover over the top to prevent accidental contact. This was in a cabinet that required a tool to open it, might give you an option.
TBH there's lots of options for you to use so whatever your budget allows.
All of the original boxes were supplied as a TT with no earth, as all the items were class 2 there was no requirement for an earth.
As the kit we were installing was class 1 BT went round and added an earth electrode, normally a rod installed behind the power panel. They also added SMART RCD and 6 amp MCB for us to terminate into.
Have you carried out a Ze on the supply to see if you're getting a good earth through the cabinet root?
This was mounted onto a DIN rail on the ply sheet behind the power panel.
Some had main switches and some didn't but you might be able to get away with using the existing fuse carrier for the light to provide an isolation point for you to install the supply for the defib unit.
On another project we did install a DIN rail in the cab with RCD and fuse carrier etc with a Perspex cover over the top to prevent accidental contact. This was in a cabinet that required a tool to open it, might give you an option.
TBH there's lots of options for you to use so whatever your budget allows.