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B. Tests with the electrical supply connected
1. Earth fault loop impedance
The earth fault loop impedance is given by:
Zs = Ze + (R
+R
)
1
2
The value of Zs can be found by:
I. measuring the earth fault loop impedance Zs
at the furthest point
II. measuring the earth fault loop impedance Ze
at the incoming supply and adding (R
1
III. taking the earth fault loop impedance Ze
provided by the distributor and
adding (R
+R
).
1
2
LINE
CONSUMER
UNIT
NEUTRAL
EARTH BAR
EARTH
MET
SUPPLY SYSTEM
INSTALLATION
Diagram 11: Measurement of External Earth Loop Impedance Ze
Preparation for the Test
1. Main Switch in the Consumer Unit is
switched OFF.
2. Main Earthing Conductor is disconnected from
the Main Earthing Terminal (MET) to eliminate
any parallel earth paths through equipotential
bonding etc.
12
Test Procedure
1. Select the appropriate range on the
test instrument.
2. Connect the test leads between the incoming
line side of the Main Switch and the
disconnected end of the Main
Earthing Conductor.
3. Perform the measurement.
4. The test instrument will automatically display
the value of Ze and the corresponding value
of the PFC.
+R
).
2
On Completion of the Test
REMEMBER TO RECONNECT THE MAIN
EARTHING CONDUCTOR TO THE MAIN
EARTHING TERMINAL
Type of Earthing
Maximum Allowable Ze
System
Value ( )
TN-C-S
TN-S
TT
Measurement taken at furthest
accessory from the Consumer Unit
for each Sub Circuit.
(Only one Sub Circuit shown for clarity)
SUPPLY SYSTEM
INSTALLATION
Diagram 12: Measurement of Earth Fault Loop Impedance Zs
Preparation for Testing
1. All power using equipment must be
disconnected from sub circuit(s) under test.
2. Main Switch is turned ON i.e.
ALL CIRCUITS ARE LIVE
Test Procedure
1. Select the appropriate test instrument range
for the measurement of Zs.
2. Connect the test leads between line and earth
at the accessory furthest away from the
consumer unit. (Alternatively test between line
and earth at each accessory point in turn until
the maximum value of Zs is obtained).
3. Operate the instrument test button and obtain
the value of Zs.
NOTE: Readings obtained using this method may
be less than Ze + (R
earth paths. This must be taken into account
when comparing the results with design data.
0.36
0.80
Functional testing
21.00
Functional testing requires that the operation of
RCDs should be tested and switchgear, controls
etc should be functionally tested to verify that they
work and are correctly mounted and installed.
2. RCD testing
Preparation for Testing
1. All power using equipment must be
disconnected from sub circuit(s) under test.
2. Main Switch is turned ON i.e.
ALL CIRCUITS ARE LIVE
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SUPPLY SYSTEM
Diagram 13: Measurement of R.C.D Tripping Time
Test Procedure
1. Select the appropriate test instrument range
for the measurement of tripping time (mS).
2. Connect the RCD tester to any accessory
point (Use the test lead provided with a 13A
+ R
) because of parallel
plug for socket circuits).
1
2
3. Operate the instrument test button and obtain
the values of tripping times (at 0.5IΔn, IΔn and
5 IΔn where appropriate).
4. Many RCD test instruments have an automatic
test sequence which will perform tests at 0.5
Please see over
Tried. Tested. Trusted.
C.U.
WITH
RCD
INSTALLATION
13
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