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I have recently been asked this question from an electrcian.

What consitutes IT equipment?


He was designing new supplies for an office.

CRT Monitors & PCs have a high earth leakage current and need the special arrangements laid out in the wiring regulations.


This applies to ANY circuit (not just supplying I.T. equipment) where the Circuit Protective Conductor current is expected to be high. Most Class I equipment, that is not "hand-held" and has a UK plug, have similar "touch current" or "protective conductor current" limits to those quoted in BS EN60950-1 "I.T. Equipment - safety - Part 1: General requirements" - i.e. 3.5 mA.

The reason that some I.T. equipment is a particular problem, is that it's low power and Class I, so there's an immediate tendancy to put lots of kit on a single circuit - even if you only have 10 devices "leaking" 1 mA, you're up to 10 mA.

To identify whether this regulation applies, the first thing that you're looking for is lots of Class I equipment on the same circuit (Class II equipment has much lower touch current, 10 times less, so much less chance it'll contribute to the problem). A device to be considered INCLUDES Class I monitors, Class I laptop PSUs (as used for some docking stations), Class I printers, etc. Also, be careful about some of the multi-way outlets sometimes fixed to desks and equipment racks, that may include additional filters: whilst not using power, they contribute to the protective conductor current.

All sockets supplying this type of equipment should have two earth connections.

With Class I (earthed) equipment, if the earth continuity disappears, any current that would have travelled down the Circuit Protective Conductor (earth wire) can travel through a person touching conductive parts of the Class I equipment.

If the available "touch current" is high enough, it can kill. There doesn't need to be a further fault in the equipment to achieve this if the "touch current" ("protective conductor current") is high enough.

There needs to be two methods of protection against shock. The first was providing the earth. The second needs to be a second earth, or some form of insurance that loss of earth continuity is unlikely, or automatic disconnection if continuity is lost.

Therefore, with high earth leakage currents ( 10 mA was decided on), you need to either protive 10 sq mm CPC (risk of loss of CPC continuity is minimised), or provide two conductors, each to separate terminal (a knock-on effect from using 2.5 / 1.5 sq mm solid) or automatically disconnect the supply if earth continuty is lost (earth monitoring system).


My point to all this is, where do you find the information on the equipment?, secondly our duty of care when assembling rack mounted equipment?


I have looked on WEB sites, service and installation manuals for information or do we have to assume that it does not go above a certain amount (10mA)?


Any installation teams out there?

Hi Oscar
I find your post very interesting and very worrying. Most computer technicians/engineers are more interested in building up the rack and configuring the systems to the customer requirements, without giving much thought to wiring regulations.

Is it the responsibilty of the hardware supplier to ensure that full instuctions are given for the installation or is it the responsibity of the technician to be aware of current regulations? Maybe the time will come when we need a computer technician and an electrian to install systems.

Don't forget, it's up to the technician/engineer to comply with the installation instructions.

When was the last time "we" read the instructions?