Wiki

The tech blog post reads: Due to an overheating problem in our European data center many of our servers turned off to protect themselves.

As this impacted all Wikipedia and other projects access from European users, we were forced to move all user traffic to our Florida cluster, for which we have a standard quick failover procedure in place, that changes our DNS entries..

Source: http://www.telegraph.co.uk/technology/wikipedia/7514826/Wikipedia-goes-down.html