Better bonding even for TT installations O.M.S? (Where perfect operation is imperative for R.C.D.s.)
Actually, TT is one of the situations where equipotential bonding can work best. Where you have comparatively low earth fault currents you end up with a low voltage difference (e.g. between exposed- and extraneous-conductive-parts) - so a much reduced shock risk, even if ADS doesn't operate promptly (either by design - e.g. large or distribution circuits, or due to faulty protective device). The problem with TN systems with relatively low Ze is that most of the 230V supply voltage is divided across the faulty circuit's conductors within the installation during an earth fault - typically over 100V between MET and exposed-conductive-part of faulty equipment - and main bonding can't really reduce that.
Better bonding even for TT installations O.M.S? (Where perfect operation is imperative for R.C.D.s.)
Actually, TT is one of the situations where equipotential bonding can work best. Where you have comparatively low earth fault currents you end up with a low voltage difference (e.g. between exposed- and extraneous-conductive-parts) - so a much reduced shock risk, even if ADS doesn't operate promptly (either by design - e.g. large or distribution circuits, or due to faulty protective device). The problem with TN systems with relatively low Ze is that most of the 230V supply voltage is divided across the faulty circuit's conductors within the installation during an earth fault - typically over 100V between MET and exposed-conductive-part of faulty equipment - and main bonding can't really reduce that.
