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20 Output Circuit Grounding! A" ]- s5 P, ~; `& c$ X, y
20.1 The requirements for circuit grounding specified in 20.2 – 20.12 apply to the output circuit of fixed; G: L6 w0 }- [
units and of units having standard configuration grounding type receptacles for the output ac power
, y. Z1 t* C8 O4 C, Fconnections.
$ e& \' J! R3 P6 k- S8 R. l {8 s20.2 An output ac power circuit shall be grounded when:3 }& W, n6 w: c1 D" P8 K
a) The circuit has no electrical connection, including a solidly connected grounded circuit$ \5 O$ O5 j' P0 |. @
conductor, to supply conductors originating in another wiring system;
1 B0 n% P/ E. H" [b) The circuit is rated 50 – 600 volts; and
$ M6 w( w, X# s! {5 F) dc) The circuit is as described in (1) – (3). See requirements for Alternating-Current Circuits and
& { }3 d0 {" `1 KSystems to Be Grounded in the National Electrical Code, ANSI/NFPA 70, for other circuits:
& e( i! P% n L1) A circuit that is grounded so that the maximum voltage to ground on the/ i' }, v0 g' Y! c( h3 i0 ^+ U6 ?
ungrounded conductors does not exceed 150 volts. This requires that one conductor of+ R5 u; T M0 b' [2 c4 u
each of the following circuits be grounded:$ j0 o: D8 F$ N' `
i) 120 volts, 2-wire; ^* Z; p2 u# }& A8 s
ii) 240/120 volts, single-phase, 3-wire;
4 k+ ^+ b0 K- Q. Y; Niii) 208/120 volts, two-phase, 3-wire;
9 B* b1 y* h, w5 L" Kiv) 208/120 volts, three-phase, 4-wire.
- P0 `% a6 x0 m$ c6 W1 o2) A circuit nominally rated 480 wye/277 volts, 3-phase, 4-wire in which the neutral is7 b/ Q+ G- V' W( Q1 I6 X
used as a circuit conductor.( k4 V+ q+ A8 ?2 m' n- l1 `2 A! a
3) A circuit-nominally rated 240/120 volts, 3-phase, 4-wire in which the midpoint of one
9 B0 |' C* f2 g4 d) { K mphase is used as a circuit conductor.. i5 A2 Z) \. z" X$ N6 F
For other units, an output ac power circuit complying with (a) is able to be grounded when the construction8 E5 I h( y& T9 u4 X% t0 M
complies with the requirements described in 20.3 and 20.11.
7 k% h5 q1 d) \/ I20.3 With reference to 20.2, the conductor to be grounded shall be as follows:; l4 @) m+ H, p/ d/ o: Z' q
a) Single-phase ac system, 2-wire – one conductor.
% l! @& C; H+ B& Qb) Single-phase ac system, 3-wire – the neutral conductor.
- E; g) g( N0 Qc) Multiphase ac system having one wire common to all phases – the common conductor.7 ~5 P9 i6 F1 o" J
d) Multiphase ac system where one phase is used as in (b) above – the neutral conductor.
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