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− First letter: relationship of the power distribution system to earth;4 B/ |* Q1 I( L( s
T means direct connection of one pole to earth,4 W2 B/ z/ u5 g$ g
I means system isolated from earth, or one point connected to earth through an
7 D+ z' r; K* @/ I- R" bimpedance.5 b+ }: e6 @/ i. I' \
− Second letter: earthing of the equipment;$ p* f( ^/ R+ B* e
T means direct electrical connection of the equipment to earth, independently of the
: j6 h# x' H! E( Nearthing of any point of the power distribution system,! X' x) i3 D' z+ l& Y' d. J
N means direct electrical connection of the equipment to the earthed point of the power* ?+ `, @, M1 @! M2 V
distribution system (in a.c. systems, the earthed point of the power distribution system( Z1 P( j0 l& V: K) K
is normally the neutral point or, if a neutral point is not available, a phase conductor).
2 i! Y9 l' g" O1 v− Subsequent letters if any: arrangement of neutral and protective conductors;+ B$ t" K. |- g$ Q$ ^3 \& v: }+ \
S means the protective function is provided by a conductor separate from the neutral or9 ^0 c: W9 u4 i4 j& s
from the earthed line (or in a.c. systems, earthed phase) conductor,
e+ f1 E% q% R5 D4 S" XC means the neutral and protective functions are combined in a single conductor
6 X5 _: }+ _. |: ], Q1 h(PEN conductor).! {) A2 [( d3 Y. t7 y
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