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Am I allowed to drill a hole through the back of the DNO meter cabinet and fit a CT clamp? Should I?

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Got a free Shelly Pro 3EM but have no exposed wiring indoors, the outdoor meter cabinet has the incoming "tails" but has no usable power outlet.
Am I allowed to drill though the back of the meter cabinet so that I can mount and power the shelly indoors and feed the CT clamp in from the cabinet or is this all DNO only? Don't have a consumer unit indoors, just an old wired fusebox and I know I'm not allowed to touch that.

Which cable would I put the CT-clamp on? I would be drilling through the top left corner inside the cabinet as it seems least like path of any cables in the wall. This is a porch and the house is to the right in this picture.

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I would be drilling through the top left corner inside the cabinet
Not acceptable, those cabinets are designed to have holes in the predefined places only, which for that one is in the bottom where those holes already exist.
There are some which can have one hole in the back but that isn't the one you have got.
None of them should have holes in or near the top because that would allow water to enter from the cavity.
 
Not acceptable, those cabinets are designed to have holes in the predefined places only
So would an electrician look to fit a consumer unit rather than trying put any clamps in this cabinet?
I think that only an electrician can make changes to the fusebox right?

Just for my understanding then, which of those cables at the bottom is incoming and which will be going to the fusebox?
 
What happens to the tails indoors? Straight in to the fuse box? I would put it in there but you probably don't have an isolator so it's not a risk I would take, as an amateur.
 
The fusebox is up high on the opposite side of the wall from the meter cabinet, the incoming tails presumably go in to there from the rear of the box. Would consider a mini CU, but I expect an electrician would need to do EICR and want to replace and rewire the lot.
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What are the possible options here to fit a CT-clamp?
I thought about finding where the cabling enters the house from the fusebox, that would be accessible under the upstairs floorboards, but that will probably be twin and earth or 3 core. I don't think you can use a CT-clamp around multiple cores right?
Would an electrician be willing/allowed to fit a CT-clamp directly into this fusebox (would there be space??) or would I need to have the fusebox replaced? Would an electrician be required to do a full EICR before touching this?
 
What are the possible options here to fit a CT-clamp? I thought about finding where the cabling enters the house from the fusebox, that would be accessible under the upstairs floorboards, but that will probably be twin and earth or 3 core. I don't think you can use a CT-clamp around multiple cores right?
No, you can't - BUT it will not be "twin an earth or 3 core". As you can see in the meter box, the 'tails'/wires going from meter to your fuse box (bottom left hole in cabinet) are three separate single-core cables - L, N and earth. If, as you suggest, you can find those cables somewhere between the meter and fuse box, then that's where you could put on your CT clamp.

However, that fuse box (and maybe the rest of your electrical installation) is seriously ancient and really needs to be 'updated' (replaced).
 
If, as you suggest, you can find those cables somewhere between the meter and fuse box, then that's where you could put on your CT clamp.
No, it's all in the shared wall that the meterbox and fusebox are on either side of.
However, that fuse box (and maybe the rest of your electrical installation) is seriously ancient and really needs to be 'updated' (replaced).
The house is 30-35 years old and the electrics are un-altered and never been a problem. I have asked for quotes from local electricians for at least a CU update, but never get replies, maybe they have bad experience from other similar installs nearby. I did get a couple of offers of call-out from 50+ miles away but they wanted paying up front just to come and have a look and as there is no urgent need, it hasn't been a priority.
 
The house is 30-35 years old and the electrics are un-altered and never been a problem. I have asked for quotes from local electricians for at least a CU update, but never get replies, maybe they have bad experience from other similar installs nearby.

Unlikely, just keep trying, until you find one willing to quote. Maybe send them a photo of your present 'fusebox', but identify what is on the circuits.

Your CT, needs to be placed around just one of the grey cables - it will not work, if looped around both, because it will cancel out.
 
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What are the possible options here to fit a CT-clamp?
It's a pity that you have a Shelly. I use an OWL monitor (and others may be similar) with the CT connected only to a little battery-powered box, which then communicates wirelessly with the rest of the world - so no need to run a cable from the CT.
 

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