Instructions

GMC-I Messtechnik GmbH 33
10.3 Earthing Resistance, Mains Powered – 2-Pole Measurement with 2-Pole Adapter or Country-Specific Plug (Schuko) without Probe
Key
R
B
Operational earth
R
E
Earthing resistance
R
i
Internal resistance
R
X
Earthing resistance through equipotential bonding
systems
R
S
Probe resistance
PAS Equipotential bonding busbar
RE Overall earthing resistance (R
E1
//R
E2
//water pipe)
In the event that it is impossible to set a probe, earthing resis-
tance can be estimated by means of an “earth loop resistance
measurement” without probe.
The measurement is performed exactly as described in section 10.4,
“Earthing Resistance Measurement, Mains Powered – 3-Pole Mea-
surement: 2-Pole Adapter with Probe”, beginning on page 34. How-
ever, no probe is connected to the probe connector socket (17).
The resistance value R
ELoop
obtained with this measuring method
also includes operational earth electrode resistance R
B
and resis-
tance at phase conductor L. These values must be deducted from
the measured value in order to determine earthing resistance.
If conductors of equal cross section are assumed (phase conductor L
and neutral conductor N), phase conductor resistance is half as great
as supply impedance Z
L-N
(phase conductor + neutral conductor).
Supply impedance can be measured as described in section 9
beginning of page 29. In accordance with DIN VDE 0100, operational
earth electrode R
B
must lie within a range of “0 Ω to 2 Ω ”.
1) Measurement: Z
LN
amounts to R
i
= 2 · R
L
2) Measurement: Z
L-PE
amounts to R
ELoop
3) Calculation: R
E1
amounts to Z
L-PE
– 1/2 · Z
L-N
; where R
B
= 0
The value for operational earth conductor resistance R
B
should be
ignored in the calculation of earthing resistance, because it is
generally unknown.
The calculated earthing resistance thus includes operational earth
conductor resistance as a safety factor.
In parameter setting steps 1 to 3 are performed auto-
matically by the test instrument.
Select Measuring Function
Select Operating Mode
Set Parameters
❑ Measuring range: AUTO, 10 kΩ (4 mA), 1 kΩ (40 mA), 100 Ω
(0.4 A), 10 Ω (3.7 ... 7 A). In systems with RCCBs, resistance
or test current must be selected such that it is less than trip-
ping current (½ I
ΔN
).
❑ Connection type: 2-pole adapter
❑ Contact voltage: UL < 25 V, < 50 V, < 65 V
❑ Test current waveshape: Sinusoidal (full-wave), 15 mA sinusoidal
(full-wave), DC offset and positive half-wave
❑ System type: TN/TT, IT
❑ Transformer ratio: irrelevant in this case
Start Measurement
P
R
O
F
I
T
E
S
T
Ri
W
a
t
e
r
P
i
p
e
E
2
E
1
B
R
E
Limit value:
R
E
> Limit Value
U
L
⏐ R
L