Operation Manual

39
- Loop impedance (Zs) measurement trips an RCD.
5.4.2 Loop impedance (Zsrcd)
Zsrcd sub-function performs measurements in supply systems equipped with an RCD. The measu-
rement current is small enough to prevent the RCD from tripping.
Modern measurement methods allow for stable and reliable results despite low measured signals.
The prospective fault current is calculated on the basis of measured resistance as follows:
P PE
L
n
PFC
R
scaling factorU
I
-
x
=
where
U
n
Voltage range
115 V 100 V ≤ U
L-PE
< 160 V
230 V 160 V ≤ U
L-PE
≤ 264 V
BecauseofdifferentdenitionsoftheprospectivefaultcurrentI
PFC
in different countries, the user
can set the scaling factor in the Setup menu (see chapter 4.4.2).
How to perform the loop impedance measurement:
Step 1 Select Zs/Ik (L-PE) (loop impedance) with the function selector switch. Use the /
keys to select the Zsrcd sub-function. The following menu is displayed:
Fig. 5.31: Loop impedance measurement menu
Connect the test cable to the BENNING IT 110/ BENNING IT 120 B.
Step 2 Set the following measuring parameters:
- Fuse type
- Fuse current rating
- Fuse trip-out time
Appendix A contains a list of different fuse types.
Step 3 Followtheconnectiondiagramshowningure5.29toperformloopimpedancemeasu-
rement. Use the Help function if necessary.
Step 4 Check the displayed warnings and online voltage/terminal monitor before starting the
measurement. If OK, press the TEST key. After performing, the measurement results
appear on the display together with the PASS/FAIL indication (if applicable).
Fig. 5.32: Example of loop impedance measurement results