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10
QUESTION 11a:
WHAT INSTRUMENT CAN BE USED TO TEST THE ELEVATED VOLTAGE ON THE NEUTRAL?
ANSWER:
Any meter with a voltage function similar to:
a) Toptronic TBM811 DMM
b) TBM3030
c) TBM251
QUESTION 11b:
HOW IS THIS TEST DONE AND WHAT VALUE OF MEASUREMENT IS ACCEPTABLE?
ANSWER:
a) Switch off the main switch.
b) Measure the voltage between the supplier neutral and the external earth of the
installation (ie. earth spike) and record on certificate of compliance / test report.
c) The reading should not exceed 25V.
d) If the reading exceeds 25V notify the supply authority by completing Annex K
(see addendum D – Pg 16).
e) If the reading exceeds 50V disconnect the supply and notify the supply authority as above.
QUESTION 12a:
WHAT INSTRUMENT SHOULD BE USED TO TEST THE EARTH ELECTRODE RESISTANCE?
ANSWER:
Any 3 terminal earth resistance tester similar to:
a) Toptronic T1105
b) Toptronic T416 (Earth Resistivity)
c) Toptronic T1120
d) Toptronic T2000
e) Toptronic MacroG3
QUESTION 12b:
HOW IS THE TEST DONE AND WHAT VALUE OF MEASUREMENT IS ACCEPTED?
ANSWER:
a) Connect the Toptronic T1805 as shown in the diagram (figure 1 – Pg 12). Ensure that the
cables are not touching or twisted as this will affect the measurement due to induction.
b) Make sure to insert the auxiliary earth bars in the moist part of the earth.
c) Spikes must be inserted in a straight line (minimum spacing is 2m).
d) If the ground is dry or sandy moisten with water (Test spikes only).
e) Where it is not possible to insert the auxiliary earth bars due to a hard surface like concrete
or stony ground lay the earth bars in a suitable position and cover them with wet cloths
(preferably with salt added to the water).
f) Please note, this is not possible on tarred, tiled or painted surfaces.
g) To check for earth voltage, depress the AC voltage button. If the reading is less than
10 volts proceed with the earth resistance test but if the reading is higher do not proceed.
First rectify the problem as this can affect the reading.
h) Now test for the correct wiring connection between the E, P and C terminals and
earthspikes by depressing the battery check button. If the O
K
light is li
t
up, proceed with
the earth resistance measurement.
i) Select the appropriate ohm scale. The meter will now indicate the earth resistance.
j) It is accepted that a circuit should carry a fault current of twice the rated circuit current. To
calculate what the maximum acceptable value of measurement proceed as per the
following formula:
V
V
Remax
= 2 x
I
2 x
I
(Amps) rated
Where Remax
=
Maximum earth electrode resistance
V
=
Measured Voltage
I
=
Rated Circuit Current
Example: 60 Amp Circuit (
I
)
230 VAC System (V)
V
Remax
= 2 x
I
= 230
(2 x 60)
= 1.92
Ω
Therefore the earth electrode resistance must be below
1.92
Ω
to allow a fault current of 120 amps to flow.
*Note: When the supplier provides an earth terminal,
then this text is optional.
Summary of Contents for ACADEMY T419
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