This British Standard specifies requirements for the installation, exchange, relocation, maintenance and removal of credit or prepayment diaphragm and ultrasonic gas meters with a maximum capacity not exceeding 6m³/h. NOTE1 For the purposes of this British Standard, installation includes design, inspection and commissioning. It is recognized that each of these tasks can be performed by the same person. This part of BS6400 is applicable to primary and secondary meter installations: supplied with 2nd family gases from low pressure gas distribution systems with a maximum operating pressure not exceeding 75 mbar, a design minimum pressure of 19 mbar and a design maximum incidental pressure of 200 mbar; fitted downstream of the emergency control valve; that utilize a primary meter regulator downstream of the emergency control valve; where the operating pressure at the outlet of the meter is nominally 21 mbar. 1) NOTE2 Low pressure gas networks in Great Britain operate with a maximum operating pressure not exceeding 75 mbar, a design minimum pressure of 19 mbar and a design maximum incidental pressure of 200 mbar. NOTE3 Installation pipework is specified in BS6891. NOTE4 Service pipes (including the emergency control valve) are specified in the Institution of Gas Engineers and Managers’ publication on gas services, IGE/TD/4 [18]. NOTE5 All pressures quoted in this standard are gauge pressures and all pressure absorption values are for natural gas unless otherwise specified. NOTE6 Additional guidance on domestic gas systems can be found in BSEN1775, BSEN1776 and BSEN12279. NOTE7 Additional guidance on gas installations in multi-occupancy buildings is given in IGEM/G/5 [N7].