What happens when a server is switched off?

I am an electrician and the job I am on the phones are dead, no dialling tone etc. I had to isolate a sub-board to test and work on installation. Now on the main board there was an MCB labelled server do not switch off. I didn't work on this main board and also didn't switch the MCB off. But the phone... show more I am an electrician and the job I am on the phones are dead, no dialling tone etc. I had to isolate a sub-board to test and work on installation. Now on the main board there was an MCB labelled server do not switch off. I didn't work on this main board and also didn't switch the MCB off.

But the phone lines are dead!!!

Whats happened?
2 answers 2