BS 7671 Amendment 4: Server Room Earthing Requirements

Server rooms and communications rooms in commercial buildings present a scaled-down version of the data centre earthing challenge. Section 545 in Amendment 4 applies equally to these smaller facilities, but the implementation differs significantly from purpose-built data centres.

The key distinction is that server rooms typically exist within a building whose earthing system was designed purely for protective purposes. Section 545 requires that the functional earthing for ICT equipment is integrated with — but does not compromise — the existing protective earthing arrangement. In practice, this means installing a dedicated functional earth bar in the server room, connected to the building's main earthing terminal by a conductor sized per Section 545, not the building's general supplementary bonding requirements.

Rack bonding is often the weakest point in server room earthing. Section 545 requires that each rack frame is bonded to the functional earth bar with a conductor of at least 16 mm² copper (or equivalent). The connection must be made using a dedicated bonding terminal, not via the rack mounting bolts or paint-coated structural members. This is a common deficiency found during inspection — painted surfaces provide intermittent or high-impedance connections that cause EMC issues and unreliable fault current paths.

Cable tray and containment bonding in server rooms must provide continuity across joints. Section 545 specifies that cable tray joints used as part of the functional earth mesh must have a DC resistance not exceeding 5 milliohms per joint. Standard cable tray clamp joints typically achieve this, but nylon-insert lock nuts or painted surfaces can push resistance above the limit.

For mixed-use buildings, the server room functional earth must not introduce earth loops that cause circulating currents in the building's protective earth system. Section 545 provides guidance on single-point versus multiple-point bonding strategies, with single-point bonding recommended for server rooms below 50 m² floor area.

ECalPro's Earthing Calculator computes conductor sizing for the functional earth bar feed, rack bonding requirements, and verifies that the server room earthing integrates correctly with the building's protective earthing system.