Measuring Methods - Benning ST 755+ Operating Manual

Appendix

13.5 Measuring methods

13.5 Measuring methods
Differential current measuring method
The connections on the mains side of the test sample are checked by a differential current
transformer. To do this, the total current and differential current of all currents flowing in and out
of the test sample are measured. If there is a current difference between the L and
N conductors, a leakage or fault current is proven to flow. If leakage or fault currents flow off via
different fault points, they cannot be detected individually.
Direct current measuring method
The leakage current is measured directly via a measuring resistor (shunt). For test samples that
are not placed onto an insulated surface, leakage currents can flow off via parallel earth
connections. This reduces the measured leakage current and results in incorrect measuring
results.
Alternative leakage current measuring method
The measuring circuit for the alternative leakage current measuring method is galvanically
isolated from the mains and the L and N conductors are bridged. By default, the potential-free
testing voltage is 230 V‑AC. In case of a different testing voltage, the measured leakage current
is converted to correspond to a test result with mains voltage.
The measuring method may only be used after the insulation test has been passed and if there
are no mains voltage-dependent electrically operated switching devices in the test sample.
DGUV Information 203-070
"Wiederkehrende Prüfungen ortsveränderlicher elektrischer Arbeitsmittel – Fachwissen für
Prüfpersonen" (Periodic inspections of portable electrical equipment – Expert knowledge for
testing personnel):
https://publikationen.dguv.de/regelwerk/dguv-informationen/246/wiederkehrende-pruefungen-
ortsveraenderlicher-elektrischer-arbeitsmittel-fachwissen-fuer-pruefpersonen
DGUV Information 203-071
"Wiederkehrende Prüfungen ortsveränderlicher elektrischer Arbeitsmittel – Organisation durch
den Unternehmer" (Periodic inspections of portable electrical equipment – Organisation by the
entrepreneur):
https://publikationen.dguv.de/regelwerk/dguv-informationen/787/wiederkehrende-pruefungen-
elektrischer-anlagen-und-betriebsmittel-organisation-durch-den-unternehme
5284 / 08/2023 en BENNING ST 755+ / ST 760+ 117