A 1472, A1579 Leakage current clamp
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4.4.3 Influence of external electric field
The electric field caused by voltage on measured conductors or any other
conductors/ parts in vicinity can interact with the current clamp through
capacitive coupling. This can happen through the sensor, housing, test
cables, measuring instrument etc.. The capacitive coupling factor should be
as small as possible and depends on electric shielding and common mode
rejection of the measuring stage,
Fig. 10: Influence of external electric fields
4.4.4 How to recognize accuracy problems ?
If following problems are noted then it is likely that external fields are
influencing the results:
The size of load currents is higher than several Amperes (especially
critical for the differential measurement).
The result depends on the position of the clamps (in regard to the
measured conductor(s), measured electrical equipment, nearby
current carrying conductors, switchboards etc). If the results
strongly fluctuate in regard to the current clamp position it is unlikely
to get an usable result.
The reading is not zero although no current is flowing through the
clamp.
4.4.5 How to minimize the influencing quantities
Do not use current clamp without information about immunity
against external fields.
The line and neutral conductors should be placed as close as
possible and in the middle of the clamps. If possible they should be
twisted to increase the symmetry (for differential measuring method)
– see Fig. 11.
The protective conductor should be placed in the middle of the
clamps (for the direct measurement).
Avoid placing the current clamp near to other line conductors and/
or current carrying conductors. If using a clamp sensor connected to
a measuring instrument the placement of the cable is important too.
Placing the current clamp/ cables close to grounded surfaces
usually lowers the coupling and improves the immunity.
The current clamp / test cables should be placed as far as possible
from the tested object
– see Fig.12.
