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20 Output Circuit Grounding1 f/ U/ ^) T! I% x; V7 F+ v# {2 [
20.1 The requirements for circuit grounding specified in 20.2 – 20.12 apply to the output circuit of fixed9 Z! \6 S: R/ T! T9 g: l
units and of units having standard configuration grounding type receptacles for the output ac power
6 s4 r3 E% D3 U N5 n# h J. `connections.
9 G+ E' u9 u7 g* i20.2 An output ac power circuit shall be grounded when:
' Y# o5 Z) b' J. }a) The circuit has no electrical connection, including a solidly connected grounded circuit
) e; n$ m0 e; N3 M2 k' [conductor, to supply conductors originating in another wiring system;, ]# I- d8 j j
b) The circuit is rated 50 – 600 volts; and' i: p' T3 v# r( N' l3 P& \' c
c) The circuit is as described in (1) – (3). See requirements for Alternating-Current Circuits and
0 \3 F# |- `! C1 uSystems to Be Grounded in the National Electrical Code, ANSI/NFPA 70, for other circuits:5 R, E4 e3 }+ D& R! h7 d& [
1) A circuit that is grounded so that the maximum voltage to ground on the. ]" T& Z8 P& R5 G
ungrounded conductors does not exceed 150 volts. This requires that one conductor of2 n7 i! c4 W P3 B
each of the following circuits be grounded:$ f3 e. Z/ ~7 g6 U( P- O9 V
i) 120 volts, 2-wire;
( g$ J( }& G( Q; p' n9 f9 }ii) 240/120 volts, single-phase, 3-wire;
) [$ M2 o% J+ O4 ~iii) 208/120 volts, two-phase, 3-wire;; N5 S* c1 P/ q8 ~+ P
iv) 208/120 volts, three-phase, 4-wire.2 w4 }& D V; u. i2 F7 y# i
2) A circuit nominally rated 480 wye/277 volts, 3-phase, 4-wire in which the neutral is" C) ^! E) o: x- q3 J
used as a circuit conductor.) |+ g5 y5 K7 M+ C" S% k0 F. `
3) A circuit-nominally rated 240/120 volts, 3-phase, 4-wire in which the midpoint of one+ P3 f, E5 n0 s& N0 x4 S
phase is used as a circuit conductor.( c/ p3 ^% X& R% w y. ]
For other units, an output ac power circuit complying with (a) is able to be grounded when the construction
# q) P+ r2 T+ V* ^ P7 d/ [* jcomplies with the requirements described in 20.3 and 20.11., u; @7 b c' d: d# M# z# P! D8 z/ X
20.3 With reference to 20.2, the conductor to be grounded shall be as follows:
8 |. t2 Y/ U8 b3 _: } W- Z9 C( Sa) Single-phase ac system, 2-wire – one conductor.2 g5 Q* B) C1 m" x5 n9 R6 E2 v
b) Single-phase ac system, 3-wire – the neutral conductor.- V% V. A- \6 u
c) Multiphase ac system having one wire common to all phases – the common conductor.
& M N4 Q+ U1 N! T' wd) Multiphase ac system where one phase is used as in (b) above – the neutral conductor.% Q$ k3 p: q, V2 L# R, r8 o
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