Megger ATEC 210415 Series, Manual

Page: 21 / 82

M
14
AVTM21-415Ja Rev. A June 2005
of the power supply is the high voltage output and is
connected to the center conductor of output cable W101. The
positive terminal of the power supply is used as a guard and is
connected to the shield of the output cable with a terminal at
the outboard end.
The kilovoltmeter M101, the range selector switch S101 and
the two range calibration resistors R105 and R106 are located
on the panel and complete the voltmeter circuit.
Current passing from the high voltage output through the
apparatus being tested and then to earth is measured by the
multi-range current meter M102 and the range
selection/protection network assembly U1. The scale of this
meter is marked in megohms rather than current. The meter
M102 and U1 are located on the panel. The Earth cable W102
completes the path for the megohm measuring circuits. For
safety the path from Earth to the metering is paralleled by the
green wire of the power cord W1. Within U1 is the
megohmmeter transient protection capacitor C1 and voltage
limiting Zener diode CR2. The Zener CR1 is connected so that
any ac will not cause a false meter indication. In series with
M102 is a swamping resistor R2 and a calibration adjustment
R1. The ranges are selected by shunting the series combination
of M102, R1 and R2 by precision resistors R3 for X1; R4 and
R5 for X10; R4, R5, R6 and R7 for X100. No shunt is used for
X1K range.
In series with M102 is a two-wire phone jack J1 that is shorted
unless a plug is inserted. For use see Section 9.
For the use and significance of the guard see Sections 9 and 10.
The Test Set is energized directly by W1 with the green wire
tied directly to the panel to provide a panel ground. The white
neutral wire is uninterrupted and is considered the return path
for the Test Set supply. The black wire is considered hot and
power is fed to the set via the CB1 circuit breaker that also is