I was thinking about deliberate nEMP (Nuclear Elecro Mgnetic Pulse) as I mentioned in the second line.

I suspect you are referring to a series of failures caused by a massive natural solar storm which eventually has been called 'The Carrington Event' after the man who recorded the details.

http://en.wikipedia.org/wiki/Solar_storm_of_1859

This event is often held up as the indicator of what could happen. Indeed the article mentioned in Teslinkiker's post refers to another report by Lloyds that talks about $0.6-2.6 trillion USD damage world wide from such another event.

What most commentators forget is that the people responsible for the utilities that could be affected are very clever people and are acutely aware of the possible problems from natural Electro-Magnetic events and have built resiliency into their systems. It is not August 1859 any longer.

No utility owner will want egg on their face and be unable to supply their services for more than a few hours and thus they take all reasonable precautions to prevent it happening. The favorite mentioned is to shut down the grid during the storm peak for a few hours, there is plenty of warning for this to happen.

Whilst I am sure that we will see some (many) problems from a repeat 'Carrington Event' I am confident that it will not be the doom and destruction many like to predict.