Protective Equipotential Bonding
02.08.2012 |
Regulation 411.1 states that automatic disconnection of supply is a protective measure in which basic protection is provided by basic insulation of live parts or by barriers or enclosures and fault protection is provided by protective earthing, protective equipotential bonding and automatic disconnection in case of a fault
There are four protective measures generally permitted by BS 7671:2008 (2011), given in Regulation 410.3.3: (i) Automatic disconnection of supply (Section 411) (ii) Double or reinforced insulation (Section 412) (iii) Electrical separation for the supply to one item of current using equipment (Section 413) (iv) Extra-low voltage (SELV and PELV) (Section 414).
A note at the end of this Regulation acknowledges that, in electrical installations, the most commonly used protective measure is automatic disconnection of supply.
Regulation 411.1 states that automatic disconnection of supply is a protective measure in which basic protection is provided by basic insulation of live parts or by barriers or enclosures and fault protection is provided by protective earthing, protective equipotential bonding and automatic disconnection in case of a fault.
Main protective equipotential bonding
The purpose of earthing the exposed-conductive-parts of an installation is to ensure that, in the event of a fault (line conductor to an exposedconductive- part), sufficient fault current flows to operate the disconnection device (fuse, circuit-breaker, RCD). Earthing exposed-conductive-parts also reduces the touch voltage (Ut) between these and extraneous-conductive-parts during a fault. The purpose of protective equipotential bonding is to further reduce the touch voltage between exposed-conductive-parts and extraneous-conductive-parts in the event of:
i. a fault on the installation
ii. an open circuit PEN conductor in a PME supply.
Regulation 411.3.1.2 requires main equipotential bonding to be carried out, however its
importance is often underestimated.
To view the full article from the IET’s Wiring Matters Summer 2012, download the attachment below.
View the full Summer 2012 Issue of Wiring Matters by visiting the IET website here.