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Fuse Failure in Power Modules

When BS6396 was published as a full British Standard in 1990 the allowable socket outlet configurations – up to 4 sockets fused at 5A and, up to 6 sockets fused at 3.15A – were introduced as a result of comments on the draft documents by the HSE. The purpose of the fuses is to restrict the use of the desk/workstation socket outlets to office equipment only with a maximum current of 5A.
Where socket configurations utilise a 3.15A rated fuse this clearly will be the maximum operating current for each socket. This should be taken into account when specifying desk electrical systems.

In most circumstances this allows the use of normal office desk top equipment. Equipment requiring an operating current in excess of these values should be connected directly to the building supply.

Therefore desk mounted sockets must not be used for heaters, kettles, coffee makers and cleaning equipment such as vacuum cleaners. Users of the desks and workstations should be made aware of these restrictions.

OE Electrics power modules are fitted with anti-surge ceramic HBC fuses as standard during manufacture. Replacement fuses should only be of the same type and rating as the OEM fitment. 3.15A fuses should only be uprated to 5A where no more than 4 sockets are connected from the building supply via the 13A plug as required by BS6396. Under no circumstances should the fuses be substituted with glass bodied fuse types.

The coloured fuse rating tags should be changed to indicate the correct fuse rating for the installation.

Failure of the fuses is not indicative of faults with the power modules but of overload from the connected equipment. This may be due to high initial current drawn by the equipment plugged into the sockets hence the original fitment of anti-surge type fuses.
Where fuse failure is occurring and 3.15A fuses are fitted consideration should be given to reduce the number of sockets to 4 per feed from the mains supply. This will then allow the use of 5A rated fuses. Where the number of sockets required at the desk is in excess of 4 with fuses rated at 5A then additional power modules feeding from a separate13A supply plug may be introduced.
In failing, the fuses have served the purpose intended – to prevent the use of high current equipment as set out by the British Standard, to protect the circuits and installation and to protect the staff using the desk.

Employers must be able to demonstrate that any electrical installations or equipment in use in the workplace comply with the Regulations. The simplest approach to show a credible compliance is to meet the requirements of relevant Standards which in the case of Electrical Systems in office furniture connected to the supply by means of a 13A plug is:-

BS 6396– Electrical Systems in Office Furniture and Office Screens.

BS6396 restricts the number of outlets for safety to a maximum of 6 outlets per mains supply feed from the 13A plug; each socket must be individually fused. Trailing sockets do not provide fuse protection for individual sockets and are therefore unsuitable for this application.

Also the use of trailing sockets also often encourages “daisy chaining” of the sockets by unqualified users leading to potentially dangerous situations.

Ref: HSE Guidance on the Electricity at Work Regulations HS(R)25

For other country specific units please contact the technical team who should be able to advise.
What is the situation with sockets inset into desk tops?
BS6396:2008 states in Section 5.5.4 “Socket outlets shall be positioned so as to minimise the risk of electrical hazards from liquid spillage.”

This means that socket outlets should not be mounted inset or horizontally facing upward in desks. When testing to BS6396 is carried out, the standard UKAS approved test is that cup of liquid is spilled over the sockets or in the vicinity of them if they are in an cable basket or tray. The liquid should not be retained on or in the sockets. Clearly where the sockets are angled any liquid would run off.

This will equally apply to sockets installed on office furniture in compliance with BS7671.

BS6396:2008 provides simple rules for the installation of electrical systems in office furniture.

This standard applies to electrical power distribution systems that are connected to the fixed wiring of the building via a 13A fused plug.

The standard also stipulates how cables should be routed through the furniture.

All compliant office furniture should have facilities for suitable cable management and electrical power distribution systems. These facilities can be fitted during the manufacture of the furniture or at a later date as the furniture is being installed.
The electrical accessories used in office furniture must be manufactured to the relevant electrical standards as set out by BS6396:2008.

Supply connection: The supply cable must be fitted with a 13A fused plug.
The exposed length of the power supply cable between the 13A wall socket and desk will be no more than 2m.

Socket outlets:
To comply with the standard, all installed sockets must be individually fused.
A maximum of 6 sockets each individually fused at 3.15A may be connected from a 13A supply. Where only 4 sockets are

connected the fuse rating can be 5A.
Sockets installed in or on office furniture are intended to supply equipment whose rating does not exceed 5Amp. Most office equipment will run within the 5Amp maximum. This does not include appliances such as kettles, fan heaters or vacuum cleaners
The socket outlets installed in or on the office furniture must be easily accessible to minimise the risk of injury. They should positioned to be free from risk of hazards such as liquid spillage.

Earthing: The furniture can either be manufactured as earthed or unearthed.
Earthed furniture will have the provision for metal components to be connected to the supply earth via the installed sockets and supply cable.

Unearthed furniture will have an electrical system installed that meets the requirements for reinforced or double insulation.
Segregation of cables: Electrical cables must be segregated from all other cables. Segregation can be achieved by providing a minimum of 50mm separation between cables, a cable management system such as compartment trunking, or cable screening. If there are any gaps between the segregation these must be no more than 150mm.

Testing: In order to comply with BS6396 all office furniture electrical installations must be tested before use; this applies to reconfigured installations as well as new installations.

To ensure continued compliance and safety in the office environment periodic tests should be carried out on the furniture electrical installation by suitably trained personnel and the results documented.

For Further information please contact OE Electrics or refer to BS6396:2008 official documentation

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