mapj1:
The two could and should share an earth if they can both be touched by a person with long arms.
With a 16A supply, strictly you do not really need the MCBs inside and I am not sure how you make them discriminate with the ones outside, but a small CU is a very handy place to marshall earths and provide a main switch.
Comments about other earths nearby are key, you need to be aware of that. It may be safer to use the PME earth if the ground is covered in cement or tarmac, and if there are already PME earthed street lights or similar within touching distance.
The correct answer is probably TT the entire installation.
UKPN:
Quite correctly, you choose not to use the PME supply, The ESQCR regulations make it clear that this kind of structure, with a steel covering needs an independent earth. The DNOs requirement is 2 meters separation from any metalwork connected to the PME network, which I am confident you can establish.
Regards, UKPN ?
That is an interesting perspective. The ESQCR may have an impact on a customer but they do not apply to customers. As far as I can see the supplier is not to offer a PME terminal to a caravan or boat but I don’t see anything else mentioned. But that’s beside the point, once a supply is delivered to an installation then I doubt that the supplier will take a great deal of interest in what the customer connects to it thereafter. Maybe there is a UKPN scanner van that checks such things, if so there are a lot of caravans parked in driveways with orange leads going through walls and windows that should be investigated.!
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