The table below shows the line-to-ground voltages in relation to the line-to-line
voltage for each grounding system.
Electrical power system typeU
L3-G
U
L2-G
U
L1-G
U
L-L
TN-S system (symmetrically grounded)0.58·X0.58·X0.58·XX
Corner-grounded delta system (nonsym-
metrical)
01.0·X1.0·XX
Midpoint-grounded delta system (non-
symmetrical)
0.5·X0.5·X0.866·XX
IT systems (ungrounded or high-resist-
ance-grounded [>30 ohms]) nonsymmet-
rical
Varying level
versus time
Varying level
versus time
Varying level
versus time
X
TT system (the protective earth connec-
tion for the consumer is provided by a
local earth electrode, and there is anoth-
er independently installed at the gener-
ator)
Varying level
versus time
Varying level
versus time
Varying level
versus time
X
98 Electrical installation – North America
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