where body resistance is low and therefore requires magnitude and duration of touch voltages to be very limited. In special circumstances (not domestic installations) bonding with deliberate lack of connection to earth (earth free local equipotential bonding) may be used. Bonding, by the IEC 60364 terminology used in BS 7671, should not be seen as just an extra to earthing. In recent US practice, which differs considerably from IEC principles and terminology, "bonding" is used more widely as a term for all the aspects of earthing that are not literally connections with the earth itself ("grounding"); so the connection of protective earth conductors to the supply neutral (since the TN-C-S system is the only permitted form in their residential installations) is now named bonding rather than earthing. This is not the case in the UK. Supply, metering and distribution Single phase (standard for domestic and light commercial) A domestic supply typically consists of a large cable connected to a service head, the sealed box containing the main supply fuse, treated as the supply to the premises. This will typically have a value from 40–100 A. Separate and neutral cables (tails) go from here to an electricity meter. More tails proceed from the meter into the consumer side of the installation and into a consumer unit (distribution board), or in some cases to a Henley block (a splitter box used in low voltage electrical engineering, slang named for W.T.Henley & Co. also sometimes called an "Isco" block, both names derived from brands of these blocks) and thence to more than one distribution board. The distribution board (a.k.a. fusebox) contains one or more main switches and an individual fuse or miniature circuit breaker (MCB) for each final circuit. Modern installations may use residual-current devices (RCDs) or residual current breakers with overcurrent protection (RCBOs). The RCDs are used for earth leakage protection, while RCBOs combine earth leakage protection with overcurrent protection. In a UK-style board, breaker positions are numbered top to bottom in the left-hand column, then top to bottom in the right column. Supply voltage Since some point in the 1970s, the supply voltage in UK domestic premises has been 240 V AC (RMS) at 50 Hz. In 1988, a Europe-wide agreement was reached to unify the various national voltages, which ranged, at the time, 220–240 V, to a common European standard of 230 V (CENELEC Harmonization Document HD 472 S1:1988). The