Circutor MPC-20 - 8 Correction of the Read Outs

--- MPC 20 & 50 TESTER - M-981136 (vers. BD) --- Page
27
8.- CORRECTING THE READ OUTS
Results from testing touch or step voltages may be incorrect due to the
existence of erratic, vagabond or parasite currents passing through the ground.
The B.O.E. 291, of 5 of December of 1987 establishes:
1.1.12 "... unless a test method is used that eliminates the effect (in testing)
of these parasite currents, e.g. polarity inversion, it will mean that the injected
current will be 1% of the current set for the installation and will not be less than
50 A for stations and substations and 5 A for transforming stations."
As a result of currents not indicated by the B.O.E. being used, it will be
necessary to use phase inversion for testing.
It is also found that in practice, the tested erratic voltages are always
negligible in terms of those created by injected currents (as long as they
conform to the set minimum).
However, in certain cases it will be possible to do a pretest on existing
voltages without injecting a current. To do this tests by pressing "Erratic
voltages" are done. Only when measurements of erratic voltages are above
10% of measurements with current injection, the following calculation must be
made:
Vp =
(º)( º)
()
VV
Ve
0 180
2
22
2
+
−
Vp = Step or touch voltage
Ve = Voltage tested "ERRATIC VOLTAGES"
V0° = Voltage tested "ON 0°"
V180° = Voltage tested "ON 180°"