Installation of sub circuit wiring
Check the installation & approval of distribution board / back box either recessed or surface and termination of all conduits & trunking completed. Confirm DB reference with load schedule detail. Check all conduits as per circuits are installed.
Clean distribution boards and make sure all conduits are free from blockage. Use of air blowers to clean conduits is helpful.
All wiring of multi-point circuits shall be carried out in a ‘looping-in’ system and no joints and connections other than those required for the final connection at the DB, ceiling rose, switches, fuses, socket outlets, motors, etc.
Wires shall be drawn-in carefully and professionally to avoid damage to insulation. Wires shall be ‘combed’ as drawing-in operation proceeds. The Neutral and Earth Continuity Conductor of each circuit shall be drawn along with the Phase conductors of that circuit in individual conduits.
Two circuits of different phase colours cannot be drawn into one conduit. When drawing groups of circuits in a common trunking, ensure that individual circuit wires are bunched together with approved cable ties and segregated. Tape shall not be used to bunch circuit wires. Sufficient termination length of wires is to be left for the purpose of DB dressing works. Individual circuits should be marked at the DB end as per the Final Approved Load Schedule.
All wire sizes and phase colour should be checked against Final Approved Load Schedules prior to drawing in operations. (Ensure All load schedules are signed and approved by the Project Engineer prior to proceeding with any wiring works)
- 3Core Heat Resistant Flexible (105degrees) cables are to be used to make final connections between the ceiling rose and light fitting control gear, etc.
- Flexible connection to load points like water heaters, heating Elements / Appliances, and other Power Appliances should be done with 3 cores Heat Resistant flexible cables of appropriate size. Ensure that all final load portable appliances are connected through an appropriately rated flex connection outlet installed near the appliance.
- Number of wires that can be drawn into a conduit shall not be more than the capacity for that conduit or Trunking and shall comply strictly with the IEE Wiring Regulations regarding capacity of conduits and Trunking and Space Factor.
- Earth conductors (ECC) shall be used throughout the installation and the size of these wires should be half the size of the Phase conductor and should be of the same grade and temperature rating of the phase conductors of the same circuit.
- GI conduits should not be used to provide earth continuity to the circuits, ECC conductors should be installed with every individual circuit ECC conductors are colour coded Yellow/Green. GI conduits and all other metallic containment system should be Earth Bonded separately to integral earth system.
- The cross-sectional area of earth conductors shall be in strict accordance with the approved schedule.
- Once all wires of the DB is drawn in, conduct a check against load schedule and segregate phase, neutral and earth wires. Install wire marking ferrules and straighten the wires neatly.
- Clean the DB Back box, and install the DB Bus bar assembly along with the breakers, ELCB etc – tighten all Screws fixing the Breakers to the bus bar assembly and torque tighten all screws.
- Using an Insulation Tester (Megger) all Cables and wire runs should be individually tested for insulation failure. Insulation failure between Phase to Phase, Phase to Neutral, phase to earth, Neutral to Earth. Continuity tests, Polarity tests etc are to be done before termination of wiring accessories and Final DB Breakers / ELCB. The readings /measurements are to be recorded on the test reports which are to be signed, dated by the Supervisor, Project Engineer and Consultant Engineer. These Test Reports are to be later stamped and forwarded to local distribution company prior to LV inspections
- Firstly, Gland, earth tag, and terminate the main feeder XLPE/SWA/PVC/Cu cable into the Incomer Device of the DB. Care is to be taken to allow enough space for installing outgoing wires at both sides of the main bus bar assembly. (Tip: allow a little excess loop in incomer cable for future maintenance requirements.)
- Secondly terminate the ECC Conductors on the ECC earth bar, neatly and bunching the wires in a straight line. Care should be taken to provide future maintenance access to remove terminated wires. Next terminate the neutral conductors in the same way. Then terminate the phase conductors as per Load Schedule order. There should not be any exposed copper conductor visible after termination. Overall appearance of the finished Product should be of high quality workmanship standards. (Experienced Panel board Technicians should be used to do this work).
- To complete the DB Dressing, ensure that The Final Load Schedule is laminated, and fixed in a plastic pouch on the DB Door; all breakers should be identified with a legend sticker fixed in the middle of the breaker assembly. And the DB ref identification name plate is to be fixed on the front top of the DB. This Name Tag should be embossed plastic (black background with white colored letters)
- Raise inspection Request to Consultant Engineer to inspect and check the installation works.
9. Inspection & Testing Initial insulation testing is done prior to start of DB dressing works as mentioned above. Final insulation tests, polarity tests, and continuity tests is to be done prior to Consultant’s inspection.
Earth Resistance tests should be conducted utilizing the standard procedures and with Calibrated and tested professional equipment. All earth resistances should comply with regulations and Project specs.
Other tests are to be done as per Consultants requirements and Project Specifications.
In-Process works shall be monitored daily by the Supervisor, Project Engineer and Consultant Engineer for quality of workmanship and installation method against approved layout/shop drawings, approved submittals, project specifications, and prevalent applicable regulations
All works shall be inspected for conformance to specifications and applicable legal requirements.