Shocking

Was surprised today to discover that the house has two separate sets of mains.

I switched off the power at the consumer unit to change some socket face plates. Tested the first one was really off, changed the front, done. Moved on to the next one (3ft away), and got a gentle but scary 'bzzzzzzz' as I took off the front.

On further investigation found a second (older) fuse box. One to watch.