PAT testing 13 amp fuses for computers

Adrian Waltho
Member - 27 posts

Ian,

There is no legislation detailing the specific requirements for fusing of electrical appliances, other than regulation 11 of the Electricity at Work Regulations 1989 which requires that suitably-located protection against excess currents must be provided where necessary.

The National Inspection Council for Electrical Installation Contracting will answer queries about the requirements for the inspection and testing of electrical appliances on 020 7564 2320. For more details see this page:

www.niceic.org.uk/specifiers/appliance.html and www.niceic.org.uk/specifiers/elecatwork.html

The HSE also publishes guidance on practically meeting the requirements of the EWR 1989, available in its 'Memorandum of guidance on the Electricity at Work Regulations 1989', priced £4.00 from HSE Books (www.hsebooks.co.uk).

I hope that helps. If not, do come back to us.

Kind regards,

Workplacelaw Network

Anonymous

Ian,

The reason that some computer equipment is fitted with 13A fuses rather than the 5A required by the rating plate is in-rush currents. i.e. When the equipment is first turned on, you can sometimes experience larger current draw for an instaneous moment of up to or even greater than twice the connected load.

Lowering the fuse rating, although correct, may sometimes cause spurious or nusiance fuse tripping.

Please also remmeber, depending upon application, the fuse in the plug top is there to protect the cable not the appliance so a 13A fuse is fine for a computer supply cable.

I would suggest talking to HP/Compaq or your computer suppliers technical department as they should have a technical breakdown of the above for their systems.

You should also be aware that such in-rush currents can also cause spurious or nusiance fuse tripping on ring main supplies and main circuits.

If you get no help from the suppliers then a good electrical Building Services Consultant should be able to provide some specific advice for your installation.

Hope that helps

Regards

Huw Thomas

Dean Duneclift
Member - 19 posts

The regulations state that a fuse to BS 1362 of the correct rating should be fitted. (Plugs & Sockets Safety Regulations 1994). The main reason almost every appliance we use has a 13 amp fuse in is because thats what the plug manufacturer fits, as they don't know what you are going to use it for.

So, if your PC states (for example) that a 5A fuse should be fitted, then that is what you should do. As electronic equipment generally draws very little current, (The very latest PC's have a max 400w PSU which is more than enough), faults can occur in components that may not draw sufficient current to blow the fuse,(eg overheating component) Though obviously a short would take it out.

Take for example a PC with a 350 watt power supply. This could draw a maximum of 1.5 amps under normal conditions. So to blow this fuse a fault current greater than 10 times that which it normally uses must be generated. It is not too difficult to imagine a small component which draws a few millamps, getting very hot, yet it is unlikely to draw a current great enough to blow the fuse.

Remember also that that 13 amp rating is the maximum current that the fuse can constantly sustain without any problem, and not the current required to blow it.

There are many well documented cases where faults have occured and yet the fuse has not blown, resulting in some serious accidents, fires, and indeed fatalities.

If you are concerned with in rush currents, then anti surge sockets can be used, but normally domestic fuses cope with these very well.