ABB ACH480 Series - Page 68

The table below shows the line-to-ground voltages in relation to the line-to-line voltage
for each earthing system.
Electrical power system typeU
L3-G
U
L2-G
U
L1-G
U
L-L
Symmetrically grounded TN system (TN-S
system)
0.58·X0.58·X0.58·XX
Corner-grounded delta system (nonsymmet-
rical)
01.0·X1.0·XX
Midpoint-grounded delta system (nonsym-
metrical)
0.5·X0.5·X0.866·XX
IT systems (ungrounded or high-resistance-
grounded [>30 ohms]) nonsymmetrical
Varying level
versus time
Varying level
versus time
Varying level
versus time
X
TT system (the protective earth connection
for the consumer is provided by a local
earth electrode, and there is another inde-
pendently installed at the generator)
Varying level
versus time
Varying level
versus time
Varying level
versus time
X
68 Electrical installation – IEC