What does happen when an accidental connection of the conductor phase to the ground connection system of computer network and information technology (IT) systems occur?

What sort of 'accidental connection' do you mean? -  a L-PE fault in a correctly wired system? or a mis-connection whereby, for example, the L supply wire is connected to the PE terminal on the equipment? (and presumably the PE wire to the L terminal...)

  - Andy.

OK, so initially it behaves just like any other earth fault on a class I appliance - at the point of the fault the voltage goes up to something nasty (e.g. half Uo in the case of a TN system) and stays there until the protective device opens some tens, hundreds or even thousands of milliseconds later. Normally that'll provide adequate protection from electric shock.


The complication with IT systems is that you might have data connections referenced to the equipment's chassis earth. If it's just one item of equipment in isolation that's not too much of a problem - but if you have several items of equipmemet each with their own earth connection and earthed referenced data connections between them, you could see significant problems. Data circuits that expect to see a varying few volts d.c. suddenly have perhaps a hundred volts or more a.c. imposed on them - so physical damage is likely, and if the signal line happens to be in use at the time, data corrpution is probably inevitable.  That said, earthed referenced data signals between equipment is getting rarer these days - most of the modern systems (e.g. twisted pair Ethernet) use a balanced system so are much more resilient on that count. Any sensible data centre will also have lots of supplementary bonding, duplicated c.p.c.s and by-pass earthing conductors (there's a separate standard for such things) which will significantly reduce the difference in earth potentials between different items of equipment.


   - Andy.

Like any  other system, at the point of fault, L and E now are at the same voltage, and the voltage slopes down from the origin to the point of fault along the live path, and it slopes upwards from the supply earth point towards the point of fault, the voltage gradient in proportion to the resistances of the different paths.

The complexity with an IT system is that it is likely to have connections to other things, such as network cables to to hubs, printers, video displays, and all manner of things, some of which are not on the same circuit, and may not even be in the same building.


The common strategy is to make the resistance (and so the voltage change) in the earth part of the path low compared to that in the live side. Racks are earthed, as is every item in it, There may be additional earth bonding to common earth planes, as this only works indoors, network cables leaving the site are hopefully opto-isolated or ideally optic fibres. ADS is organised to remove power to just the faulty section if at all possible , especially if the system is processing valuable data (bank records anyone). The interaction of UPS and fault behaviour needs to be considered, and there can be quite a lot to it.