Table of Contents
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RCD Type
Rated residual
I Δn (mA)
operating current
General
10
30
100
300
500
Delay (Type S)
100
300
500
Appendix
1. Continuity testing
Continuity testing is used to establish the
existence of a current-carrying path. BS 7671
recommends that continuity testing is carried
out using a test instrument with an open
circuit test voltage between 4V and 24V dc or
ac and a short circuit current of not less than
200mA. Test instruments should comply with
the requirements of BS EN 61010 and BS EN
61557. Test instruments such as the Seaward
IRT 1557, PowerTest 1557 or PowerPlus
1557 can be used to perform continuity tests.
The test instrument provides a test current
from the internal battery supply, which
circulates through the conductor under test.
The test instrument measures the test current
and voltage across the circuit under test and
displays the resistance of the path between
the test probes.
14
@ 0.5 I Δn
@ I Δn (ms)
@ 5 x I Δn (ms)
Trip time
Trip time
Trip time
<200
<40
Should not trip
130 - 500
40 - 150
It is recommended that the performance of
the instrument is checked before any tests are
performed. A basic check can be performed
by shorting the test probes together and
pressing the test button; the reading on the
scale should be almost zero ohms. When the
test probes are then disconnected, the
reading should indicate beyond the maximum
value on the scale.
To perform a continuity test the test leads are
connected to the two points in the circuit
between which the continuity is being
checked.
a) A low reading at the zero end of the scale will
indicate a continuous circuit or 'good continuity'
b) A reading above the maximum scale value
indicates a broken connection or an
'open-circuit.'
www.seaward.co.uk
c) A reading lying between a) and b) indicates a
high resistance connection somewhere in the
circuit. In this case, all connections should be
re-checked and the circuit re-tested until the
value falls to almost zero ohms.
A continuity test instrument is required for the
following tests:
i) Polarity tests
ii) Continuity of circuit protective
conductors (CPC)
iii) Continuity of earthing and protective
bonding conductors
iv) Ring Circuit Continuity
2. Insulation resistance testing
In a healthy electrical installation, the only
electrical connection between phase and neutral
conductors will be where loads are situated, for
example at lamps, socket outlets or other fixed
appliances.
Elsewhere in the installation there should be good
electrical isolation between phase and neutral
conductors and between current carrying
conductors and earth.
Circuit nominal
Voltage (V)
SELV and PELV
Up to and including 500V with the exception of the above systems
Above 500V
Tried. Tested. Trusted.
If all lamps and appliances are disconnected,
there should be an extremely high resistance
between phase and neutral, phase and earth, and
neutral and earth. An insulation resistance test is
used to verify that this 'healthy' condition exists.
BS 7671 requires that an insulation resistance
test is carried out with a test instrument capable
of producing the dc test voltages shown in the
table below. For single phase domestic
installations, a 500V insulation resistance test is
required. the PowerPlus 1557 and PowerTest
1557 are capable of such tests.
Please see table below.
Before the tests are carried out the tester should
be checked in the following manner:
a) Connect the test leads together and press the
test button - a reading of zero ohms should be
obtained.
b) Disconnect the test leads and press the test
button - a reading greater than the largest
value on the scale should be obtained.
The 'dead' circuit tests can then be carried out.
Test voltage d.c
Min. insulation
(V)
resistance (M )
250
0.5
500
1.0
1000
1.0
15
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