INSPECTION AND TESTING OF ELECTRICAL WORK
2.11.1 General
2.11.1.1 Every installation shall, on completion and
before being energized, be inspected and tested. The methods of test shall be
such that no danger to persons or property or damage to equipment occurs even
if the circuit tested is defective.
2.11.1.2 Periodic inspection and testing shall be
carried out in order to maintain the installation in a sound condition after
putting it into service. Where an
addition is to be made to the fixed wiring of an existing installation, the latter shall be examined
for compliance with the recommendations of the Code.
2.11.1.3 The individual equipment and materials which form part of the installation
shall generally conform to the relevant Bangladesh Standard (BDS ) wherever applicable. If there is no relevant
Bangladesh standard specification for any item, these shall be approved by the
appropriate authority.
2.11.2 Insulation
Tests
2.11.2.1 Insulation resistance test shall be made on
all electrical equipment, using a self-contained instrument such as the direct
indicating ohm-meter of the generator type. d.c. potential shall
be used in these tests and shall be as follows:
Circuits under 230 volts 500
volts
Circuits
between 230 volts to 400 volts 1000
volts
2.11.2.2 The minimum acceptable insulation
resistance value is 5 mega ohms. Before
making connections at the ends of each cable run, the insulation resistance measurement test of
each cable shall be made. Each conductor of a multi-core cable shall be tested
individually to all other conductors of
the group and also to earth. If
insulation resistance test readings are found to be less than the specified
minimum in any conductor, the entire cable shall be replaced.
2.11.2.3 All transformers, switchgears etc. shall be
subject to an insulation resistance
measurement test to ground after installation but before any wiring is
connected. Insulation tests shall be made between open contacts of circuit breakers,
switches etc. and between each phase and earth.
2.11.3 Earth
Resistance Test
2.11.3.1 Earth resistance tests shall be made on the
system, separating and reconnecting each earth
connection.
2.11.3.2 The electrical resistance of the earth
continuity conductor together with the resistance of the earthing lead measured
from the connection with the earth electrode to any other position in the
completed installation shall not exceed 1 ohm.
2.11.3.3 Where
more than one earthing sets are installed, the earth resistance between
two sets shall be measured by means of resistance bridge instrument. The earth
resistance between two sets shall not exceed 1 ohm.
2.11.4 Operating
Tests
Current load measurement shall be made on equipment
and on all power and lighting feeders. The current reading shall be taken in
each phase wire and in each neutral wire while the circuit or equipment is
operating under actual load conditions. Clip-on ammeters may be used to take
current readings. All light fittings
shall be tested electrically and mechanically to check whether they comply with
the standard specifications. Fluorescent light fittings shall be tested so that
when functioning no flickering or choke singing is felt.
2.11.5 Inspection
of the Installation
On completion of wiring a
general inspection shall be carried out by competent personnel in order to
verify that the provisions of this Code and that of the Electricity Act of
Bangladesh have been complied with. A certificate may be issued on satisfactory
completion of the work in a format as shown in Appendix C. Items to be
inspected are detailed in the following sections.
2.11.5.1 Substation Installations : In substation
installations, it shall be checked whether:
- The installation has been carried out in accordance with the
approved drawings;
- Phase to phase and phase to earth clearances are provided as
required;
- All equipment are efficiently earthed and properly connected
to the required number of earth electrodes;
- The required ground clearance to live terminals is provided;
- Suitable fencing is provided with gate with lockable
arrangements;
- The required number of caution boards, fire fighting
equipment, operating rods, rubber mats, etc., are kept in the substation;
- In case of indoor substation sufficient ventilation and
draining arrangements are made;
- All cable trenches are provided with noninflammable covers;
- Free accessibility is provided for all equipment for normal
operation;
- All name plates are fixed and the equipment are fully painted;
- All construction materials and temporary connections are
removed;
- Oil level , bus bar tightness, transformer tap position, etc.
are in order;
- Earth pipe troughs and cover slabs are provided for earth
electrodes/earth pits and the neutral
and LA earth pits are marked for easy
identification;
- Earth electrodes are of
GI pipes or CI pipes or copper plates. For earth connections, brass bolts and
nuts with lead washers are provided in the pipes/plates;
- Earth pipe troughs and oil sumps/pits are free from rubbish,
dirt and stone jelly and the earth connections are visible and easily
accessible;
- HT and LT panels and switchgears are all vermin and damp-proof
and all unused openings or holes are blocked properly;
- The earth bus bars have tight connections and corrosion
free joint surfaces;
- Control switch fuses are provided at an accessible height from
ground;
- Adequate headroom is available in the transformer room for
easy topping-up of oil, maintenance, etc.;
- Safety devices, horizontal and vertical barriers, bus bar
covers/shrouds, automatic safety shutters/door interlock, handle interlock etc. are safe and in reliable operation in
all panels and cubicles;
- Clearances in the front, rear and sides of the main HT and LT
and subswitch boards are adequate;
- The switches operate freely; the 3 blades make contact at the
same time, the arcing horns contact in advance; and the handles are provided
with locking arrangements,
- Insulators are free from cracks, and are clean;
- In transformers, there is no oil leak;
- Connections to bushing in transformers are light and maintain
good contact;
- Bushings are free from cracks and are clean;
- Accessories of transformers like breathers, vent pipe,
buchholz relay, etc. are in order;
- Connections to gas relay in transformers are in order;
- In transformers, oil and winding temperature are set for
specific requirements to pump out;
- In case of cable cellars, adequate arrangements exist to pump
off water that has entered due to
seepage or other reasons; and
- All incoming and outgoing circuits of HT and LT panels are
clearly and indelibly labeled for identifications.
2.11.5.2 Medium Voltage Installation: In medium
voltage installations, it shall be checked whether:
- All blocking materials that are used for safe transportation
in switchgears, contactors, relays, etc. are removed;
- All connections to the earthing system are feasible for periodical inspection;
- Sharp cable bends are avoided and cables are taken in a smooth
manner in the trenches or alongside the walls and ceilings using suitable
support clamps at regular intervals;
- Suitable linked switch or circuit breaker or lockable push
button is provided near the motors/apparatus for controlling supply to the
motor/apparatus in an easily accessible location;
- Two separate and distinct earth connections are provided for
the motor apparatus;
- Control switch fuse is provided at an accessible height from
ground for controlling supply to overhead travelling crane, hoists, overhead
bus bar trunking;
- The metal rails on which the crane travels are electrically
continuous and earthed and bonding of rails and earthing at both ends are done;
- Four-core cables are used
for overhead travelling crane and portable equipment, the fourth core
being used for earthing, and separate supply for lighting circuit is taken;
- If flexible metallic hose is used for wiring to motors and
other equipment, the wiring is
enclosed to the full lengths, and the
hose secured properly by approved means;
- The cables are not taken through areas where they are likely
to be damaged or chemically affected;
- The screens and armours of the cables are earthed properly;
- The belts of belt driven equipment are properly guarded;
- Adequate precautions are taken to ensure that no live parts
are so exposed as to cause danger;
- Ammeters and voltmeters are tested; and
- The relays are inspected visually by moving covers for
deposits of dusts or other foreign matter.
2.11.5.3 Overhead Lines : For overhead lines, it shall be
checked whether:
- All conductors and apparatus including live parts thereof are
inaccessible;
- The types and size of supports are suitable for the overhead
lines/conductors used and are in accordance with approved drawing and
standards;
- Clearances from ground
level to the lowest conductor of overhead lines, sag conditions, etc.
are in accordance with the relevant standard;
- Where overhead lines cross the roads or cross each other or
are in proximity with one another, suitable guarding is provided at road
crossings and also to protect against possibility of the lines coming in
contact with one another;
- Every guard wire is properly earthed;
- The type, size and
suitability of the guarding arrangement provided is adequate;
- Stays are provided suitably on the overhead lines as required
and are efficiently earthed or provided with suitable stay insulators of
suitable voltages;
- Anticlimbing devices and Danger Board/Caution Board Notices
are provided on all HT supports;
- Clearances along the route are checked and all obstructions
such as trees/branches and shrubs are cleared on the route to the required distance on either side;
- Clearance between the live conductor and the earthed metal
parts are adequate; and
- For the service connections tapped off from the overhead
lines, cutouts of adequate capacity are provided.
2.11.5.4 Lighting Circuits : The lighting circuits
shall be checked to see whether:
- Wooden boxes and panels are avoided in factories for mounting
the lighting boards, switch controls, etc.;
- Neutral links are provided in double pole switch fuses which
are used for lighting control, and no fuse is provided in the neutral;
- The plug points in the lighting circuit are all 3-pin
type, the third pin being suitably earthed;
- Tamper proof interlocked switch socket and plug are used for
locations easily accessible;
- Lighting wiring in
factory area is enclosed in conduit and the conduit is properly earthed, or
alternatively, armoured cable wiring is used;
- A separate earth wire is run in the lighting installation to
provide earthing for plug points, fixtures and equipment;
- Proper connectors and
junction boxes are used wherever joints are in conductors or cross over of
conductors takes place;
- Clear and permanent identification marks are painted in all
distribution boards, switchboards,
sub-main boards and switches as necessary;
- The polarity has been checked and all fuses and single pole switches
are connected on the phase conductor only and wiring is correctly connected to
socket outlets;
- Spare knockouts provided in distribution boards and switch fuses are blocked;
- The ends of conduits enclosing the wiring leads are provided
with ebonite or other suitable bushes;
- The fittings and
fixtures used for outdoor use are all of weatherproof construction, and
similarly, fixtures, fittings and switchgears used in the hazardous area are of
flameproof application;
- Proper terminal connectors
are used for termination of wires (conductors and earth leads) and all strands
are inserted in the terminals;
- Flat ended screws are used for fixing conductor to the
accessories;
-
Flat washers backed up by spring washers are used for making end
connections.
Source : PWD Schedule Book
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