Supplementary equipotential

Supplementary equipotential bonding to pipework will only be required as an addition to fault protection (lEE Regulation 415.2) if the immersion heater vessel is in a bathroom that does not have ... 

See the section on supplementary equipotential bonding later in this chapter and Fig. 14.64. 

PVC cables enclosed in heavy-duty PVC conduit are suitable for installations in most agricultural buildings. All exposed and extraneous metalwork must be provided with supplementary equipotential bonding in areas where livestock is kept (Regulation 705.415.2.1). In many situations, waterproof socket outlets to BS 196 must be installed. All socket outlet circuits must be protected by an RCD complying with the appropriate British Standard and the operating current must not exceed 30 mA. 

Local supplementary equipotential bonding (lEE Regulation 701.415.2) must be provided to all gas, water and central heating pipes in addition, to metallic baths, unless the following two requirements are both met. 

Note. Local supplementary equipotential bonding may be an additional requirement of the Local Authority regulations in, for example, licensed premises, student accommodation and rented property. 

The lEE Regulations describe the need to consider additional protection by supplementary equipotential bonding in situations where there is a high risk of electric shock (e.g. in kitchens and bathrooms) (lEE Regulation... 

In rooms containing a fixed bath or shower, supplementary equipotential bonding conductors must be installed to reduce to a minimum the risk of an electric shock unless the following two conditions are met ... 

There are also provisions in section 601-04 relating to supplementary equipotential bonding. This requires the terminals of protective conductors associated with Class I and Class II equipment in Zones 1, 2 and 3 to be connected together and for them to be connected to extraneous conductive parts on those zones. The latter parts are listed as including metallic items such as service pipes (gas, water and so on), waste pipes, central heating pipes, air conditioning duct work, accessible structural parts of buildings, and baths and shower basins. 

If the earth loop impedance is too high for overcurrent protection to operate within the prescribed time, Regulation 413-02-04(i) permits this time to be exceeded provided local supplementary equipotential bonding is used to meet the requirements of Regulations 413-02-27 and 28 and the fault persistence does not cause damage. Again, the intention is to minimise the potential differences between touchable metalwork items on the occurrence of an earth fault. As an alternative. Regulation 413-02-04(ii) allows the use of RCD protection. 

Supplementary bonding must be provided in bathrooms even if there are satisfactory metal-to-metal joints because of the enhanced shock risk see section 601. Consideration should be given to the provision of supplementary equipotential bonding in kitchens, sculleries and laundry rooms with conducting floors, such as quarry tiles, particularly if they are likely to be wet, again because of the enhanced shock risk. Similar locations in commercial and industrial premises should receive the same consideration. 

Supplementary equipotential bonding is specified for all three zones, but the previous requirement for an equipotential bonded metal grid in solid floors in zones B and C has been amended to bonding such grids if they exist. 

All exposed and extraneous conductive parts accessible to livestock have to be bonded together by supplementary equipotential conductors. Where there are metal grids in conductive floors, they have to be bonded to the protective conductor. Fire precautions (subsection 605-10) call for heaters to be separated from livestock and combustible material, and for RCD protection operating at not more than 500 mA except where supplies are essential for animal welfare. 

Section 7 deals with main and supplementary equipotential bonding and section 8 with the enhanced risks in the special locations of Part 6 of the sections. In Table 3 the increased risks are analysed and in Table 4 the precautions required for each location are summarised. In section 8.4 there is some useful information about equipotentially bonded floor grids. 

Cable glands are properly made off, wire armouring and braiding is securely held by the gland and dust boots are correctly fitted. Supplementary equipotential bonding is provided where necessary. Fuses are of the correct type and rating and excess current trips correctly set. 

To measure the continuity of the earthing conductor and the main and supplementary equipotential bonding conductors, their ends remote from the consumer s earthing terminal should be temporarily disconnected to avoid parallel paths, and a test applied between these remote ends and the main earthing terminal. 

Test for continuity of protective conductors, including protective equipotential and supplementary bonding. 

The object of the test is to ensure that the CPC is correctly connected, is electrically sound and has a total resistance which is low enough to permit the overcurrent protective device to operate within the disconnection time requirements of Regulation 411.4.6, should an earth fault occur. Every protective conductor must be separately tested from the consumer s main protective earthing terminal to verify that it is electrically soimd and correctly connected, including the protective equipotential bonding conductors and supplementary bonding conductors. 

Where other potential metallic conductors exist near to electrical conductors in a building, they must be connected to the main earth terminal to ensure equipo-tential bonding of all conductors to earth. This applies to gas, water and central heating pipes and other devices such as lightning protection systems. Supplementary bonding is required in bathrooms and kitchens where, for example, metal sinks and other metallic equipment surfaces are present. This involves the connection of a conductor from the sink to a water supply pipe which has been earthed by equipotential bonding. There have been several fatalities due to electric shocks from live service pipes or kitchen sinks. 

If it is not possible to establish an equipotential zone because, for example, there is a conducting floor (such as a concrete floor) or because equipment is being used outdoors, supplementary or alternative measures must be taken. The use of residual current circuit breakers to provide sensitive earth leakage protection, in addition to the overcurrent protection, is one acceptable option the RCD would detect earth fault currents, including shock currents flowing to earth, and rapidly interrupt the circuit. Indeed, it is general practice to ensure that socket outlets that will foreseeably be used to supply external equipment should have RCD-protection fitted. 

Section 547 covers main and supplementary bonding conductors. Their purpose is to maintain touchable metalwork in the equipotential zone at the same potential so as to avoid the possibility of electric shock to anyone touching different metalwork items at the same time. It is necessary to check that joints in metal pipes are metal-to-metal to ensure low resistance otherwise bonding across is needed. Look out for plumbing in which both... 

---