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2) equipm entfo use both three-phase four-w ire and three-phase three-wire
supplies, earthed and unearthed, use the values three-wire system only. This because the actual voltage to
earth determ ined the insulation resistance and capacitive reactance each
line-to-earth; thus, low (but acceptable) insulation resistance one line can in
effect earth and raise the other two line-to-line voltage earth.6.c. voltage systems
(based VDE 0110-1)
Nominal voltage
o the
supply system
For insulation
line-to-line
For insulation
line-to- earth
All systems
Three-phase four-
wire-systems with
neutral-earthed
Three-phase tliree-wire-
system unearthed or
comer-earthed
V V
60 63
110
120
127
125 125
150 160 160
208 200 125 200
220
230
240
250 160 250
300 320 320
380
400
415
400 250 400
440 500 250 500
480
500
500 320 500
575 630 400 630
600 630 630
660
690
630 400 630
720
830
800 500 800
960 1,000 630 1,000
1,000 1,000 1,000
1) Line-to-earth insulation levelfo unearthed impedance-earthecl system equals
that line-to-line because the operating voltage earth any line can, in
practice, approach line-to-line voltage.2.3 Rated voltage
Table 4.Insert 167
4.
.18: Three-phase four three-wire a
