Electric supply to a wooden garden room

You need certificates for the work. If not assume the worst. Apart from that is there planning permission for the building to be used as a dwelling? You can supply a studio with electric no problem. However a cold water supply and intention to use as accomodation does require planning permission. Would look into that if I were you. Electric showers would almost certainly need to be supplied by a substantial armoured cable. A think white wire would just melt.

I doubt the 'thin white wire' is the cable feeding the building. That would be a substantial steel wire armoured cable, SWA, and would be black and possibly a little deeper in the ground with yellow warning tape running above it. What you found could be just a data cable or telephone cable. It should be possible to identify the circuit to the outbuilding by looking at the labels on the consumer unit. With the items described it should be at least a 40A rated circuit.

Hi, Cables need to be buried at the depth of at least 500 mm with a marker tape across top of it at a depth of 150mm marking the cable beneath. All cables in the ground MUST be Steel wire armoured ( armoured cable or SWA ). Hope this helps

I’d recommend getting an electrician to carry out a full EICR of the property prior to buying, this would uncover any potential dangers that may be present. The only cable that is suitable for burying in the ground is steel wire armoured (SWA), it’s also been buried at the incorrect depth; and from what you’ve described, it may very well be overloaded. Get an electrician in to give you a professional opinion.

Get the vendor to have an EICR ( Electrical Installation Condition Report) done on all the installation. Get them to pay for it and any issues arising from is a good negotiating tool

BS 7671: Requirements for Electrical Installations contains recommendations that a cable installed in a wall or partition must, in many cases, be provided with additional protection by means of an RCD.

Buried cables should be in a trench that is 600mm deep and should be mechanically protected from damage - usually in the form of steel wire armoured cable. Ideally it would also be in a duct. The cable you're describing doesn't sound like it meets any of those criteria, and therefore it sounds like the installation doesn't conform to the BS7671 Wiring Regulations or Part P of the Building Regulations. It is illegal to carry out electrical work which doesn't comply with Part P, but in most scenarios this only comes into play if there is a catastrophe of some kind. It is possible that your local Building Control can force the owner to make the necessary changes so that it does conform to Part P and BS7671, but I've never been down this route, so can't say how interested they will be. The vendor should have an Installation Certificate showing that all the necessary inspections have been done and test results recorded, along with a certificate showing that the work has been notified to Building Control. I HIGHLY doubt that they will have these as it sounds like a dodgy DIY job, so you should at the very least get something in writing stating who carried out the work. You should also point out that electrical work that doesn't comply with Part P may invalidate home insurance/be uninsurable. I am also concerned that there is a shower in the building, as I will bet that they have not properly earthed the building. Plus you say the wire is 'thin' and it is powering a shower.... All in all it sounds dodgy as hell, and I would guess that a new supply cable will need to be run and earthing and bonding sorted out. To start with I'd employ an electrician to inspect and test the building and tell you exactly what is wrong with it and what needs to be done to remedy the issues.