8.8.4 - Periodic inspection and testing
The importance of regular inspection and
testing of electrical installations cannot be overstated,
but unfortunately it is an aspect of electrical safety which
is very often overlooked. It is now a requirement of the
Regulations that the installer of an installation must tell
the user of the need for periodic test and inspection and
the date on which such attention is required. Probably the
good contractor will institute a system so that a reminder
is sent to the customer at the right time. Suggested intervals
between inspections and tests are shown in {Table
8.4}. The results of sample tests should
be compared with those taken when the installation was last
tested and any differences noted. Unless the reasons for
such differences can be clearly identified as relating only
to the sample concerned, more tests must be carried out.
If these, too, fail to comply with the required values,
the complete installation must be retested and the necessary
correcting action taken.
The inspection and testing must be carried
out with the same degree of care as is required for a new
installation. In fact, more care is often needed because
dangers can occur to the testers and to others in the situation
in the event of failure of parts of an installation such
as the protective system. The tester must look out for additions to
the installation, or for changes in the use of the area
it serves, either of which may give rise to fire risks.
Included may he the addition of thermal insulation, the
installation of additional cables in conduit or trunking,
dust or dirt which restricts ventilation openings or forms
an explosive mixture with air, changing lamps for others
of higher rating, missing covers on joint boxes and other
enclosures so that vermin may attack cables, and so on.
The sequence of periodic tests differs
slightly from that for initial tests {8.3.2}
because in this case the supply will always be connected
before testing starts. The tests required and the sequence
in which they must be performed are shown in {Table 8.13}.
There will be cases where necessary information in the form
of charts, diagrams, tables, etc., is not available. The
tester will then need to investigate the installation more
thoroughly to make sure that he is fully conversant with
it before he can carry out his work.
It must be clearly understood that a retest
of a working installation may not be as fall as that carried
out before the installation was put into service. For example,
it may be impossible to switch off certain systems such
as computers, and if full testing is not possible, this
should be made clear on the certificate. In such cases,
the installation should be carefully inspected to ensure
that possible dangers become apparent. In some cases it
may be necessary to carry out measurements, such as the
value of the earth leakage current, which will indicate
the health of the system without the need to disconnect
it.
A sample of 10% of switching devices must
be thoroughly internally inspected and tested. If results
are poor, the procedure must be extended to include all
switches. The condition of conductor insulation and other
protection against direct contact must also be inspected
at all distribution boards and at samples of switchgear,
luminaires, socket outlets, etc. There should be no signs
of damage, overloading or overheating.
Protective and equipotential bonding conductors
must not be disconnected from the main earthing terminal
unless it is possible first to isolate the supply. The tester
must ensure that a durable notice to the wording given in
{Table 8.12} is fixed at the mains position.
On completion a full electrical installation
certificate must be submitted. Additional matters to report
are:
1. -
full test results to enable comparison with earlier
tests, from which the rate of deterioration of the installation (if any) can be assessed.
2. - the full extent of the parts
of the system tested notes
of omissions may be very important
3. -
any restrictions which may have been imposed on the
tester and which may have limited his ability
to report fully
4.
- any dangerous conditions found during testing and
inspection, non-compliance with the
Regulations,
or any variations which are likely to arise in the future.
Where an installation was constructed to
comply with au earlier Edition of the Regulations, tests
should be made as required by the 16th Edition as far as
it is applicable and the position fully explained, with
suggestions of necessary action, in the Electrical Installation
report.
|
Table 8.12 - Notice - periodic
inspection and testing
|
| IMPORTANT |
| This installation should be periodically
inspected and tested and a report on its condition obtained,
as prescribed in BS 7671 (formerly The IEE Wiring Regulations
for Electrical Installations) published by the Institution
of Electrical Engineers. |
| Date of last inspection………………………… |
| Recommended date of next inspection………………………… |
|
Table 8.13 - Sequence of periodic
testing
|
|
1
|
Continuity of protective
conductors and earthed equipotential bonding. |
|
2
|
Polarity |
|
3
|
Earth fault loop impedance |
|
4
|
Insulation resistance |
|
5
|
Operation of switches
and isolators |
|
6
|
Operation of residual
current devices |
|
-
|
|
together with the following where
appropriate
|
|
-
|
|
7
|
Continuity
of ring final circuit conductors |
|
8
|
Earth electrode
resistance |
|
9
|
Manual operation of circuit
breakers |
|
10
|
Electrical separation
of circuits |
|
11
|
Insulation resistance
of non-conducting floors and walls |