70 Electric Wiring: Domestic
BONDING: QUESTIONS AND ANSWERS By now, we should know why bonding is necessary. The next question is to what extent bonding should be carried out? This is, perhaps, answered best by means of question and answer examples. 1. Do I need to bond the kitchen hot and cold taps and a metal sink together? The IEE Regulations do not require this bonding to be carried out in domestic kitchens/utility rooms, etc. 2. Do I have to bond radiators in a premises to, say, metal clad switches or socket outlets? Supplementary bonding is only necessary when extraneous conductive parts are simultaneously accessible with exposed conductive parts and when the disconnection time for the circuit concerned cannot be achieved. In these circumstances, the bonding conductor should have a resistance R 50/Ia, where R resistance of supplementary bonding conductor, 50 touch voltage of 50 V and Ia current causing operation of protection. 3. Do I need to bond metal window frames? In general, no! Apart from the fact that most window frames will not introduce a potential from anywhere, the part of the window most likely to be touched is the opening portion, to which it would not be practicable to bond. There may be a case for the bonding of patio doors, which could be considered earthy with rain running from the lower portion to the earth. However, once again, the part most likely to be touched is the sliding section, to which it is not possible to bond. In any case, there would need to be another simultaneously accessible part to warrant considering any bonding. 4. What about bonding in bathrooms? This is dealt with in detail in Chapter 4.