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20 Output Circuit Grounding! u( j6 B2 l" F% w0 T, a
20.1 The requirements for circuit grounding specified in 20.2 – 20.12 apply to the output circuit of fixed0 G3 R: N2 i: X5 D( O
units and of units having standard configuration grounding type receptacles for the output ac power4 J! y1 q2 i: b% S
connections.! T! R' n4 N. Q& a1 ` ~1 F4 v
20.2 An output ac power circuit shall be grounded when:- ?/ ?0 [' X7 P" m5 T
a) The circuit has no electrical connection, including a solidly connected grounded circuit
1 t5 t5 @9 Q# Q' ~; mconductor, to supply conductors originating in another wiring system;; Y- B: j6 H; }3 }, j& R
b) The circuit is rated 50 – 600 volts; and
" z- f% i/ Q; J9 v$ Cc) The circuit is as described in (1) – (3). See requirements for Alternating-Current Circuits and
$ p5 [% N( t/ R) pSystems to Be Grounded in the National Electrical Code, ANSI/NFPA 70, for other circuits:
9 n" f+ F' d1 ~: x0 h1) A circuit that is grounded so that the maximum voltage to ground on the
4 X- d6 x' S- o1 @ungrounded conductors does not exceed 150 volts. This requires that one conductor of. B' [* ~8 W8 t6 h2 h
each of the following circuits be grounded:5 w5 ]/ M- T4 E: y1 u: F$ B
i) 120 volts, 2-wire;% U' T9 q1 e4 \1 K0 E
ii) 240/120 volts, single-phase, 3-wire;0 H2 V! R2 n+ g9 P+ D
iii) 208/120 volts, two-phase, 3-wire;4 S: k& N3 x: N1 l. Z2 ]# `; p
iv) 208/120 volts, three-phase, 4-wire.
# Z/ ?) T, y1 H l" B5 t2) A circuit nominally rated 480 wye/277 volts, 3-phase, 4-wire in which the neutral is# h3 m5 N& P- G I; u% k0 L0 M
used as a circuit conductor.! S5 r8 u/ T3 j8 U7 d) s
3) A circuit-nominally rated 240/120 volts, 3-phase, 4-wire in which the midpoint of one: p4 _! I: s& ~' ], q3 H
phase is used as a circuit conductor.
' b/ C+ h% N kFor other units, an output ac power circuit complying with (a) is able to be grounded when the construction& ~; Z, V s% _. D+ M7 l* e
complies with the requirements described in 20.3 and 20.11.
$ _! u3 M4 r% a, X5 S9 X& }20.3 With reference to 20.2, the conductor to be grounded shall be as follows:
G( m& l. G* e! t) x; Va) Single-phase ac system, 2-wire – one conductor.
+ X7 p: g- D+ w( _& k( I" j$ Hb) Single-phase ac system, 3-wire – the neutral conductor.
$ Y1 u" k: T- ^c) Multiphase ac system having one wire common to all phases – the common conductor.* Q0 l! B6 b: \9 a. y
d) Multiphase ac system where one phase is used as in (b) above – the neutral conductor.
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