Rural Suffolk. About 300 metres underground on the LV cable which run back to a poletop 11 kV transformer. We are on the far end of this LV line. The 3-phase HV distribution then runs overhead cross country for tens of miles.
We are prone to two main supply disturbances:
1. outages on the HV side. UPS fitted on all network and IT equipment. It’s not unknown for outages to last from 15 minutes up to 4+ hours. The property is 3-phase connected and we have a 60 kVA backup set that kicks in through an auto changeover mains fail detect board.
2. Longer term voltage swells, especially in the summer/warmer months.
The last big strike (high summer) was particularly nasty. It wasn’t a direct hit but indirect and made worse because we have fairly long radial connections to barns and outbuildings from the supply which is a PME (TNC-S) arrangement. Long copper ‘spur’ connection are a mare with strikes because of earth equipotentials - which can result in nasty surges. We suffered a lot of equipment damage and outright destruction.
Some important lessons were learned -
1. Fit permanent type 1+2+3 lightning/surge arrestors before the main board, and also at any sub-boards, especially where these are being supplied externally.
2. The text books are right when they say it’s not a good idea to run copper data cabling outdoors, between buildings. Always use fibre between buildings if possible.
3. Big impulse spikes are impressive in their destruction.
4. Get professional advice on additional earthing arrangements.
5. Have (some critical) spares ready.
6. Sometimes unfortunately your luck just runs out!