Sunday, April 12, 2020


Cable Trunking

Conduit and Accessories Installation Factors

Conduit, accessories and trunking installation should comply with the latest issued Regulations for the Electrical Equipment of Buildings by the Institution of Electrical Engineers, unless otherwise approved by the Engineer. In addition installation should also comply with all local electricity regulations.

All metallic conduit and conduit fittings should be galvanized, heavy gauge steel, screwed, solid drawn or weld type complying with IEC 423 and IEC 614.

Conduit Types and Specifications

Types of Conduit Wiring System is as below:
Surface Conduit Wiring
If conduits installed on roof or wall, It is known as surface conduit wiring. in this wiring method, they make holes on the surface of wall on equal distances and conduit is installed then with the help of rawal plugs.

Concealed Conduit wiring
If the conduits is hidden inside the wall slots with the help of plastering, it is called concealed conduit wiring. In other words, the electrical wiring system inside wall, roof or floor with the help of plastic or metallic piping is called concealed conduit wiring. obliviously, It is the most popular, beautiful, stronger and common electrical wiring system nowadays.

Types of Conduit

Following conduits are used in the conduit wiring systems (both concealed and surface conduit wiring). 

  • Metallic Conduit
  • Non-metallic conduit

Metallic Conduit:
Metallic conduits are made of steel which are very strong but costly as well.

There are two types of metallic conduits.

Class A Conduit: Low gauge conduit (Thin layer steel sheet conduit)
Class B Conduit: High gauge conduit (Thick sheet of steel conduit)

Non-metallic Conduit:
A solid PVC conduit is used as non-metallic conduit now a days, which is flexible and easy to bend.

Size of Conduit:
The common conduit pipes are available in different sizes genially, 13, 16.2, 18.75, 20, 25, 37, 50, and 63 mm (diameter) or 1/2, 5/8, 3/4, 1, 1.25, 1.5, and 2 inch in diameter.

Following conduit and raceways specification should be utilize if where it is required or as per instruction of authorized engineer:

· Power Conduit- HDPE/ASTM F2160;

· Electrical Conduit- EB, PE & rigid PVC/UL 651A/UL 651B;

· Telecommunication Conduit- HDPE/ASTM F2160;

· Premise Raceways- UL 2024 Optical Fiber Cable Raceway.

PE Conduit uses in power transmission and communication like substation to transformer, secondary transformer to end-user cable, telephone, CATV and data transmission etc. PE conduit uses mainly for its significant physical advantages over other materials like-

· Resist brightness with age or cold weather;

· Low temperature impact resistance;

· Permanent flexibility;

· Ambient temperature range -30oC to 180oC

PE Conduit Feature

01. Multiple colour and stripes are available;

02. Pre-installed or cable in conduits are available;

03.Corrugated flexible inner ducts are available;

04.Self-supporting or built-in suspension strands are available.

Advantage of Conduit Wiring Systems

  1. It is the safest wiring system (Concealed conduit wring)
  2. Appearance is very beautiful (in case of concealed conduit wiring)
  3. No risk of mechanical wear & tear and fire in case of metallic pipes.
  4. Customization can be easily done according to the future needs.
  5. Repairing and maintenance is easy.
  6. There is no risk of damage the cables insulation.
  7. it is safe from corrosion (in case of PVC conduit) and risk of fire.
  8. It can be used even in humidity , chemical effect and smoky areas.
  9. No risk of electric shock (In case of proper earthing and grounding of metallic pipes).
  10. It is reliable and popular wiring system.
  11. sustainable and long-lasting wiring system.

Disadvantages of Conduit Wiring Systems

  1. It is expensive wiring system (Due to PVC and Metallic pipes, Additional earthing for metallic pipes Tee(s) and elbows etc.
  2. Very hard to find the defects in the wiring.
  3. installation is not easy and simple.
  4. Risk of Electric shock (In case of metallic pipes without proper earthing system)
  5. Very complicated to manage additional connection in the future.

What Is Difference between Conduit and Pipe.


In general it is very similar between plastic pipe and conduit; but in use completely different between them. So, it must be consider what it is and where it is going to use for.

  1. Conduit do not have long term internal pressure what have in pipe;
  2. Due to long term stress pipes need hydrostatic design basis where is not require in conduit;
  3. Internal clearance for pipe is required on flow of volume where in conduit it’s depends on cable possession, group of cable, diameter of cable, cable pulling system, length of cable etc;
  4. Conduit installation path in vertical, horizontal, curvature is very much important on cable nature;
  5. In short pulling length up to 55% and for long pulling length below 40% should be fill-up the conduit volume, but in pipe no need to keep any empty space.

Conduit Installation Factors

Mechanical Stress is an issue to select the placement the conduit. If exceed the maximum allowable pulling tension and bending radii, conduit may damage.

Pulling Tension should consider during conduit installation. Tail loading, length of conduit, bending radii should control to keep the safe pulling tension.

Bending Radii often face on conduit pulling route, pulling tension and mechanical stress increase in bending curve. It’s important to select bending radii to avoid conduit damage in curved area.

Conduit Trenching may various types, but open trench and continuous trench methods are very traditional. Also trench digging, placing conduit and backfilling is important in conduit trenching.

Conduit Jointing can be variety of thermal and mechanical methods, but for each proper engineering design and system should follow.

Cable Installation in conduit is an important job which can be accomplished in a few ways, such as-

  1. Cable pulling in conduit using rope or pull line;
  2. Cable pulling in conduit using specialized high volume jet of air;
  3. Cable-in-Conduit or pre-installed cable in conduit by manufacturer.

Conditions for Conduit and Trunking Wiring 


Common Aspects for Both Recessed and Surface Conduit Works

(i) The erection of conduits of each circuit shall be completed before the cables aredrawn in.

(ii)Conduit Joints

(a) All joints shall be sealed/cemented with approved cement. Damaged conduitpipes/fittings shall not be used in the work. Cut ends of conduit pipes shallhave neither sharp edges nor any burrs left to avoid damage to the insulationof conductors while pulling them through such pipes.

(b) The Engineer-in-charge, with a view to ensuring that the above provisionhas been carried out, may require that the separate lengths of conduit etc.after they have been prepared shall be submitted for inspection before beingfixed. 

(iii) Bends in Conduit 
(a) All bends in the system may be formed either by bending the pipes by anapproved method of heating, or by inserting suitable accessories such asbends, elbows or similar fittings, or by fixing non-metallic inspection boxes,whichever is most suitable. Where necessary, solid type fittings shall beused. 

(b) Radius of bends in conduit pipes shall not be less than 7.5 cm. No length ofconduit shall have more than the equivalent of four quarter bends from outletto outlet. 

(c) Care shall be taken while bending the pipes to ensure that the conduit pipeis not injured, and that the internal diameter is not effectively reduced. 

All switches, plugs, fan regulators etc. shall be fitted in flush pattern. The fanregulators can be mounted on the switch box covers, if so stipulated in the tenderspecifications, or if so directed by the Engineer-in-charge. 

After installation, all accessible surfaces of metallic accessories shall be painted incompliance with clauses under Chapter 15 “Painting”.

Standard circular boxes or machined face heavy-duty steel adaptable boxes with machined heavy type lids should be used throughout. For outdoor mounting all boxes should be galvanized, weatherproof and fitted with external fixing lugs.

Conduit terminations should be fitted with brass bushes.

The use of running threads, solid elbows and solid tees will not be permitted.

Conduit ends should be carefully reamed to remove burrs. Draw-in boxes should be provided at intervals not exceeding 10m in straight-through runs.

Conduit runs should be in either the vertical or horizontal direction unless otherwise approved and should be arranged to minimize accumulation of moisture. Provision for drainage should be made at the lowest points of each run.

Conduits should be supported on heavy galvanized spacer saddles so as to stand off at least 6 mm from the fixing surface.

Provision should be made for the support of internal conductors in instances where the length of the vertical run exceeds 5m. 

All conduits run in any circuit are to be completed before any cables are pulled in.

Flexible metallic conduit should be used where relative movement is required between the conduit and connected apparatus, and a separate copper connection provided to maintain earth continuity.

Ensure the better service life of conduit and cable installed into conduit should follow the international and local standard and wiring regulations. The maximum number of cables in any conduit should be in accordance with the latest issue of the IEE Regulations for the Electrical Equipment of Buildings.


  1. Conduit and Accessories Installation Factors are very much important for cable laying. Nice and helpful post for those who are working with these.

    1. Thanks for your important comments, keep in touch and have a nice day.


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