There are a number of electrical equipment construction types that are referred to within the Standards. These are important because they determine how the user is protected against electric shock and describe tests appropriate to apply when assessing safety.

Reducing the voltage, using RCDs and selecting the appropriate equipment class (Class I, II or III) taking the task and environment into account, are primary method of risk reduction.​

The following points are listed in priority order and should be considered when procuring and using electrical​ equipment:

• Battery operated and Class III equipment – should be used whenever possible, and is exempt from electrical equipment inspection and testing.
  
• 110v equipment - is suitable for building and construction work, outdoor use in good weather, and in workshop type environments.
  
• Class II 230V double insulated (and fully insulated) equipment - suitable for use in benign, low risk areas should be employed in preference to Class I equipment.
• ​Class I 230v earthed equipment – only to be used if double insulated and 110V equipment is not available, and to be used only in benign, low risk areas.​
• Consideration should be given to the use of a Residual Current Device (RCD) with 30mA protection when the operating environment or task poses an elevated risk of injury. Such as when using hand-held and portable equipment.
• All 230V electrical equipment, including extension leads, used outdoors must be protected with a 30mA RCD.

Class I electrical equipment includes appliances and tools, and for such equipment, protection against electric shock is provided by both the provision of basic insulation, and connecting metal parts to the protective conductor in the connecting cable and plug and hence via the socket outlet to the fixed installation wiring and the means of earthing.

Class II electrical equipment is equipment in which protection against electric shock is provided by basic insulation and an additional safety precaution such as supplementary insulation, or reinforced insulation.

Class III electrical equipment relies for protection against electric shock on supply from a Separated Extra-Low Voltage (SELV) source. However, SELV is also described as Safety Extra-Low Voltage in appliance standards and Separated Extra-Low Voltage in installation standards such as BS7671.

Class O and Class OI equipment is not allowed on STFC sites.

Extension Leads

The use of 230V extension leads should be avoided where ever possible – and they should not be connected in series (“Daisy Chained”).

If used, they should be tested as portable appliances and have three core leads (including a protective earthing conductor).

The length of any extension lead should not exceed the following unless it is protected by an RCD with a rated residual current not exceeding 30mA. The RCD should, preferably, form part of the fixed installation:

Care must be taken when using cable reels. For short period low load applications it is not necessary to fully uncoil extension leads. However, where long period and/or high load usage is required, leads should always be fully unwound. Some reels are protected with thermal trips and may state a maximum load when coiled, however, if in doubt, always uncoil the cable.

Microwave Ovens

Microwave leakage testing is excluded from this code, but should be included in the Estate Services inspection and test programme. (See SC4 – Safety and the safe Use of Work Equipment​, for more details).