HT instruments MACROTEST G3 - Manual (Page 102)

MACROTESTG3 - COMBIG3
EN - 101
12.11. VERIFICATION OF VOLTAGE DROP ON MAIN LINES
Measurement voltage drop as a result of current flow through a main line or a part of it can
be very important if it is necessary:
 Verify the capability of an existing main line to supply a load
 Dimension a new installation
 Search for possible causes of troubles on devices, loads, etc.. connected to a main line
Purpose of the test
Measure the maximum percentage value of voltage drop between two points of a main
line
Parts of the system to be checked
The test includes two sequential impedance measurements in the initial point of main
power line (typically downstream to a protection device) and in the final point of the same
line.
Allowable values
The instruments compares the calculated value of
V% maximum voltage drop to the set
limit value (according to applicable guidelines) according to the following relationship:
 
100 *
*
%
I
NOM 1 2
NOM
MAX
V
V
Z Z

 
where:
Z
2
= End point impedance of the main line being tested
Z
1
= Initial point impedance (Offset) of the main line being tested (Z
2
> Z
1
)
I
NOM
= Nominal current of protection device of the main line being tested
V
NOM
= Phase-Neutral or Phase-PE nominal voltage of the main line being tested
12.12. MEASUREMENT OF EARTH RESISTANCE IN TN SYSTEMS
Purpose of the test