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20 Output Circuit Grounding6 Q" B9 {+ Y& P. ^# I% ]- F
20.1 The requirements for circuit grounding specified in 20.2 – 20.12 apply to the output circuit of fixed
+ a/ h9 d7 ?) T$ ?3 c) T, [2 dunits and of units having standard configuration grounding type receptacles for the output ac power9 @' |' g5 A: d: ?% m9 w
connections.+ d' t N: R, q* l B
20.2 An output ac power circuit shall be grounded when:' e7 v$ K% l/ o6 {) i6 L- [
a) The circuit has no electrical connection, including a solidly connected grounded circuit
. o8 o. T: C# `& p9 }$ pconductor, to supply conductors originating in another wiring system;* f' l( |3 e4 [( C
b) The circuit is rated 50 – 600 volts; and* z3 i) ?% w: Z, x3 h3 V0 `
c) The circuit is as described in (1) – (3). See requirements for Alternating-Current Circuits and/ Z& `" v! [. Z* l2 R5 Y( ?1 t
Systems to Be Grounded in the National Electrical Code, ANSI/NFPA 70, for other circuits:+ N5 l5 G. s1 S
1) A circuit that is grounded so that the maximum voltage to ground on the, R% A" m, t; E6 I9 X) `% a
ungrounded conductors does not exceed 150 volts. This requires that one conductor of3 q5 Z ]& o& C
each of the following circuits be grounded:
) b$ ?# [/ F# N$ `7 d) L' E( Zi) 120 volts, 2-wire;
2 \6 f" K0 u) m4 r+ Tii) 240/120 volts, single-phase, 3-wire;
) @2 I3 f- c2 @ T q9 Hiii) 208/120 volts, two-phase, 3-wire;2 b( `2 f7 C" ~5 z% r
iv) 208/120 volts, three-phase, 4-wire.- U3 ?; a8 G/ k9 P k1 k8 S# ~! |
2) A circuit nominally rated 480 wye/277 volts, 3-phase, 4-wire in which the neutral is
1 |' ~' Y# }" Q1 j% rused as a circuit conductor.
; J$ g# z! j" `* Z) `. [3) A circuit-nominally rated 240/120 volts, 3-phase, 4-wire in which the midpoint of one
f U( k1 @5 Z) m! x! ?phase is used as a circuit conductor.
9 C; ~$ n7 I& d, ]9 i$ {/ e B! ^. {For other units, an output ac power circuit complying with (a) is able to be grounded when the construction
+ y3 G- W6 Y% ncomplies with the requirements described in 20.3 and 20.11.
) d8 ~, o* T3 c20.3 With reference to 20.2, the conductor to be grounded shall be as follows:
& Z( u' q# K- I8 _9 ?/ ?a) Single-phase ac system, 2-wire – one conductor.
5 n( B, e- x- w, Z! @0 c) Y1 ^0 N5 ]b) Single-phase ac system, 3-wire – the neutral conductor., b& o3 l4 Y$ d9 u/ O8 E
c) Multiphase ac system having one wire common to all phases – the common conductor.
9 W) m- @0 i! n+ G6 p, T$ t% T4 Sd) Multiphase ac system where one phase is used as in (b) above – the neutral conductor.
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