Wiring Systems: Conduits

During electrical installation, there are various wiring systems which Electrical engineers adopt according to the environment in which the installation is to be done.

Types of Wiring Systems

• All insulated wiring system
• Armoured cable system
• Catenary wiring system
• Cleated wiring system
• Lead alloy sheathed system
• Mineral insulated metal sheathed system
• Metal sheathed wiring systems
• Wood casing wiring systems
• Earthed - concentric wiring system
• Bus bar system 
• Trunking and Ducting system
• Conduit system 

Conduit System

In this post I will discuss Conduit system in details.
Conduits are pipes/tubes in which electrical cables are drawn, during wiring, to provide them with mechanical protection. Conduits are either fixed on the surface of the wall or concealed in the wall behind plaster.

Types of conduits

There are two main types of conduits; Metallic and Non-metallic conduits. Flexible conduits is also another type but this can be classified under both metallic and non-metallic. Normally conduits, especially metallic conduits, have been manufactured following the requirements of British Standards Specifications number 31 of the year 1940. This standard is now withdrawn according to the British Standard Institute website. Therefore some of the conduits I will discuss might no longer be available in the market.

Metallic Conduits

Generally metallic conduits are classified as Light and Heavy gauge conduits. And these are usually Steel and Aluminium conduits. Light gauge conduits have a thin wall whereas Heavy gauge conduits have a thick wall. Nowadays Light gauge conduits are known as Electrical Metallic Tubing (EMT) and Heavy gauge conduits are known as Rigid Metal Conduits (RMC). Also there are those that are known as Intermediate Metal Conduits that fall in between RMC and EMT. Light gauge and Heavy gauge steel conduits are also known as Class A and Class B respectively according to BSS no.31, 1940.
Light gauge and Heavy gauge conduits are mainly of two types:

1. Brazed or welded joints conduits
2. Seamless or Solid drawn conduits

Light gauge steel conduits

Light gauge steel conduits are the least expensive and easy to install. The Standard sizes for Light gauge steel conduits are; 16mm, 20mm, 25mm, 32mm, 50mm and all these sizes are for the outside diameter. Because these conduits are thin walled, threading them for fitting is not possible. Therefore other methods are used to fit them and these are slip on and lug grip. These two can be used but the most commonly used, these days, is the lug grip method.

A sketch of a Lug grip

When using these fitting methods, paint or enamel must be removed first from the ends of the conduit. This is to allow earth continuity. These type of conduits can easily rust therefore they are not suitable in damp areas and if it is fixed on the surface of the wall, enamel should be replaced whenever it gets scratched.

Heavy gauge steel conduits

Now, as compared to the light gauge steel conduits, heavy gauge steel conduits are expensive and they can provide maximum mechanical protection for cables. A wiring done with this type of conduits is durable. Being thick, they can be fitted by means of screw threading and this provides a good electrical continuity.
Heavy gauge system is suitable for new buildings whereby wiring is required to be concealed in walls. The Standard sizes for Heavy gauge steel conduits are the same as those of the Light gauge steel conduits. Sets and bends for steel conduits may be made using a bending machine.

Aluminium conduits

Aluminium conduits are also used in the same way as steel except that for them they tend to flatten when being bent. They are also manufactured in light gauges and heavy gauges. Threading Aluminium requires parafin or oil for lubrication. Galvanised iron or steel, cast aluminium are the fittings used for aluminium conduits.
Bituminous paint should be applied to the conduits to prevent corrosion especially in damp situations. Aluminium conduits must not come into contact with copper or brass for this can also result in corrosion.

Advantages of Aluminium conduits

•  Aluminium conduits are less likely to corrode as compared to steel.
• They are non magnetic and therefore do not cause interference in magnetic field.
• Light and easy to handle. This helps reduce labor costs during installation.
• They are good at earth continuity
• Aluminium conduits can screen off and shield electromagnetic radiations. 
• The system can last for a long time without breaking because of its resistance to corrosion.

However light gauge Aluminium conduits are not so strong as steel, therefore they might need to be provided with more support during installation. Aluminium can react with the alkalis in cement therefore it cannot be embedded directly in concrete.

Copper conduits

Although expensive, this system should be employed in situations where prevention of corrosion is the first priority.
Copper conduits can be fitted by threading them or soldered to the fittings and bronze fittings are the best choice.
Advantages of Copper conduits

• Copper is very resistant to corrosion therefore the copper conduit system is durable.
•  It provides excellent conductor protective circuit (cpc)

Disadvantages of Copper conduits

• The system is expensive
• In certain conditions moisture from condesation may occur inside the conduits.
• Like Aluminium, copper conduits cannot be embedded in concrete floor because the alkalis in cement can react with it and it corrodes. 

 Non metallic conduits

These are plastic conduits that is either Polyvinyl Chloride (PVC) ore Polythene. They can be obtained in the same sizes/gauges as steel conduits.

Plastic Conduits

Advantages of using Plastic Conduits

• They are easy to manipulate/work on without using special tools
• There is no risk of fire due to break down in continuity
• No internal condesation that take place
• The conduits are resistant to corrosion from most industrial liquids
• They are non magnetic therefore they cannot cause interference in magnetic field

Disadvantages of Plastic Conduits

• They are not suitable for use in temperatures above 60 degrees Celsius and below -5 degrees Celsius. This is because the conduits might lose their strength and deform under these temperatures.
• They are more liable to mechanical damage than steel conduits.

 Flexible Conduits

As I said earlier these conduits can either be metallic or non metallic. They are used for final connection to electric motors. They are manufactured in sizes ranging from 10mm to 50mm internal diameter.

Non metallic flexible conduits

Though metallic flexible conduits are also available, they may not make a good circuit protective conductor. Therefore when installing this conduit, a separate circuit protective conductor must run between brass adapters used to join the flexible conduit to a rigid screwed conduit.