PRINCIPLE OF CONDUIT WIRING

DEFINITION OF CONDUIT WIRING

Is the type of wiring whereby insulated cables are drawn into metal or plastic tube. Plastic conduit is now mostly used in domestic installation. 

  Advantages of conduit wiring
1. It provides mechanical protection for the cable.
2. Provide efficient earth continuity 3. Minimize fire risk
4. It is durable

Disadvantages
1. It is expensive 
2. It is liable to corrosion  
3. Difficult to conceal

 Types of conduit
 1.  Light gauge conduit
2. Heavy guage conduit
3. Flexible metallic conduit
4. Aluminium conduit

Light gauge conduit
Light gauge is a product made from strip steel which is form into a tube. It has an open seam and is only used for small installation at or below 250v. 

 It cannot easily be bent because of it light weight and it also unsuitable for used in damp situation, and does not provide a very high degree of mechanical protection.
Type of light gauge conduit  .

  (A)     Close joint- this type has the edges butter together without a mechanical joint. close joint cannot be bent or set as the seam tend to open.

 (B)      Brazed or welded joint – the seam, is mechanically joined by brazing or welding.  

          FITTINGS-
 Grip fitting are mostly used to ensure electrical and mechanical continuous at all joints. 

 This is achieved by the use of lug grip which can be tightened to the end of the conduit by the screw .The electrical continuity may properly be made by removing paint or enamel from the end of the conduit.

HEAVY GUAGE SCREWED CONDUIT-This type of conduit is heavy, all joint to fitting are made of screwed threads.

   There are two types of heavy gauge conduit.
 A.   welded joint 

  B. solid drawn

In each case both ends of length of conduit are screwed electrical thread.                                                

 a.   The heavy gauge welded conduit is almost universally employed for general work.   

  b.   The solid drawn is used mostly in situations where explosive gases are present and flameproof installation e.g garage 

 MATERIALS FOR FIXING CONDUIT.
Distance saddle- they are used to keep dust from collecting between the conduit and the wall.
Ordinary saddle- they are used to hold the conduit firmly against the wall.
Space bar saddle – are used to hold the conduit away from damp plaster.

CONDUIT  TERMINATION.
Conduit run are always terminated at switches, sockets and ceiling outlets by using an appropriate box. Conduit run and terminations must be electrically and mechanically continuous throughout the installation. It is also essential that the end of the conduit are properly butted to ensure electrical and mechanical continuity and also to allow the free passage for the drawing in cables.

 INSTALLING CONDUIT. 

      W hen installing conduit the following steps should be taken 

   1   planning the layout-Use the architects drawing to determine whether the entire requirement for the conduit installation has been meet by consumer.                                                        

   2 Marking out-This is done for the proper routing of conduit pipe for all outlets with the aid of a chalk line. 

 Preparing the conduit –Here cutting threading and bending of the conduit pipe take place.  

PROCEDURE FOR THREADING A PIPE                
1 Cut the conduit pipe with fine hacksaw blade.                                                                                       

  2Taper the end of the conduit with a flat file.                                                                                             

 3At the end of the cutting, the end of the conduit should be smoothed with either a reamer or flat file. 

 4Wipe the threaded ends with a clean rag to remove excess lubricant or metal filings.                  
 5 Lubricate the part to be threaded using appropriate lubricant such as mineral oil or tallow.  I.E.E 

REGULATION REQUIRES THAT                                                                                                             

 1 Conduit must be securely fixed and protected from mechanical damage.                                        

 2 Extra- low voltage and low voltage cables must not be run in the same conduit. 

 3 The conduit system must be completed before cables are drawn in.
4 Inspection boxes, draw in boxes, should be so situated that they remain accessible throughout the life of the installation.                                                                                                                            

 5 Where conduit pass through floor walls, partition or ceiling the boxes should be made good with cement or similar material.  

References

Cauldwell, Rex (2002). Wiring a House (For Pros By Pros). Newtown, CT, USA: Taunton Press.

  R.K. Clidero Applications of Electrical Construction, General Publishing Co., Don Mills Ontario Canada, 1975, 

 R. S. Means Electrical Cost Data 22nd Edition,  pages 106-107 table 16 200 Conduits 

 John H. Chiang, (Ed), RS Means Electrical Cost Data 30th Annual Edition, RSMeans Construction Publishers, Kingston MA USA, 2007,

                                           
Thanks.                          

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