1. What is earthing and what is its purpose?
Earthing is a safety measure that connects exposed conductive parts to the main earthing terminal to provide a path for fault current to flow to earth. This prevents electric shock and damage to equipment.
2. What is the difference between earthing and bonding?
Earthing connects exposed conductive parts to the main earthing terminal, while bonding connects extraneous conductive parts to the main earthing terminal. Bonding prevents a potential difference from occurring, which could create a hazardous touch voltage.
3. Which regulations relate to electrical earthing?
BS 7430: 2011+A1:2015 is a code of practice for protective earthing of electrical installations. This standard is closely linked to the requirements of BS 7671, where relevant, and both should be considered when dealing with earthing requirements.
BS 7430 provides recommendations on meeting the requirements for earthing of electrical installations. The three areas include, protective earthing of low voltage installations, the interface between LV and HV substations (11 kV / 400 V), and protective earthing and changeover switch arrangements for generators.
4. What factors need to be considered for earthing requirements?
There are many factors that will impinge upon the resistance of the connection to Earth. These will include the nature and properties of the soil within a location, rainfall, and the nature of the earth electrode. For example, light clay soils will have a relatively low resistivity (c 5 Wm), whilst granite has a resistivity in the region of 1000 Wm.
The presence of low volumes of rainfall will also have a significant impact on soil resistivity. For example, clay soil in locations having a normal rainfall exceeding 500 mm / year has a typical resistivity in the region of 5 – 20 Wm, whilst in locations having a rainfall less than 250 mm will have a resistivity range of 10 – 100 Wm.
For more information on earthing take a look at YouTube