Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Conduit Runs and Fitting
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Conduit Runs and Fitting
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Subject: Basic Electricity
Class: Senior Secondary 2
Term: 1st Term
Week: 7
Theme: Electrical Wiring
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An electrical conduit is a tube or channel used to protect and route electrical wiring in a building or structure. It provides mechanical protection for the conductors, shielding them from physical damage, moisture, chemicals, and corrosive vapours. Conduits also offer a pathway for future wiring upgrades or replacements, enhancing the flexibility and longevity of an electrical installation.
In Nigeria, various types of conduits are used, each suited for specific applications and environments.
Rigid Metal Conduit (RMC): Description: Heavy-gauge, threaded steel tubing. Very robust and provides excellent physical protection.
Application: Often used in outdoor applications, hazardous locations, and industrial settings where maximum protection is required (e.g., factories, petrol stations). It is less common in residential wiring due to cost and installation difficulty.
Joining: Threaded couplings and fittings.
Bending: Requires heavy-duty conduit benders.
Intermediate Metal Conduit (IMC): Description: Thinner wall than RMC, but still robust and threaded. Lighter and easier to work with than RM
C. Application: Similar to RMC but where weight and cost are considerations. Suitable for commercial and light industrial applications.
Joining: Threaded couplings and fittings.
Bending: Requires conduit benders.
Electrical Metallic Tubing (EMT): Description: Lightweight, thin-walled metal tubing, not threaded. Often called "thinwall conduit." Application: Widely used for concealed and exposed installations in commercial and industrial buildings. Also found in some residential applications.
Joining: Compression-type or set-screw couplings and connectors. No threading required.
Bending: Easily bent with hand benders.
Flexible Metal Conduit (FMC): Description: Helically wound, flexible metal tubing. Also known as "flex." Application: Used for connections to motors, transformers, or other equipment where flexibility is required to absorb vibration or facilitate movement. Also for short, difficult runs.
Joining: Special flexible conduit connectors. Rigid Polyvinyl Chloride (PVC)
Conduit (uPVC): Description: Non-metallic, non-corrosive, lightweight plastic tubing. Available in different grades (light, medium, heavy duty).
Application: Very common in Nigerian residential and commercial buildings for both surface (exposed) and concealed (embedded in walls/slabs) installations. Offers good protection against moisture and chemicals.
Joining: Solvent cement (adhesive) for permanent joints. Special expansion couplings are used where temperature changes might cause expansion/contraction.
Bending: Can be bent with the aid of a heating spring or heat gun. Pre-formed bends (elbows) are also available.
Flexible PVC Conduit: Description: Flexible, corrugated plastic tubing.
Application: Used for short, flexible runs, typically connecting to appliances or in areas where rigid conduit installation is difficult. Not suitable for long, unprotected runs.
Practical Consideration in Nigeria: PVC (uPVC) conduit is the most commonly encountered type in residential and small commercial wiring due to its affordability, ease of installation, and resistance to corrosion, especially in humid environments. EMT is also prevalent, particularly in more modern commercial buildings. Conduit fittings are accessories used to connect, support, terminate, and change the direction of conduit runs. They are essential for a complete and functional conduit system.
Couplings: Used to join two lengths of conduit together in a straight line.
Examples:* Threaded couplings (for RMC/IMC), set-screw couplings (for EMT), compression couplings (for EMT), solvent cement couplings (for PVC).
Connectors: Used to attach a conduit to an electrical box (junction box, switch box, socket box).
Examples:* Threaded connectors, set-screw connectors, compression connectors. These often include a locknut to secure the conduit to the box.
Elbows (Bends): Used to change the direction of a conduit run, typically at 90 degrees or 45 degrees.
Examples:* Pre-formed metal elbows, pre-formed PVC elbows. For field bends, conduit benders are used for metal, and heat guns/springs for PV
C. Saddles (Clips/Straps): Used to secure conduits to surfaces (walls, ceilings). They come in various types (e.g., one-hole, two-hole, distance saddles) to ensure proper spacing and support.
Example:* One-hole saddle for PVC conduit, two-hole saddle for metal conduit. Spacing typically not exceeding 1.5 to 3 meters, and within 30cm of boxes/fittings.
Bushings: Fitted to the ends of conduits where they terminate into boxes to protect wire insulation from sharp edges.
Locknuts: Used in conjunction with connectors to secure conduits to electrical boxes, ensuring good electrical continuity for metallic conduits (grounding) and mechanical stability.
Reducers: Used to connect conduits of different sizes. Adaptable Boxes (Junction Boxes, Switch Boxes, Socket Boxes): Enclosures where conductors are spliced, connected to switches/sockets, or terminated. Conduits terminate into these boxes.
Junction Box:* Used for making wire splices or junctions.
Switch Box:* Accommodates switches.
Socket Box:* Accommodates electrical sockets/receptacles. Inspection Fittings (e.g., inspection elbows/bends/tees):* Special fittings with removable covers used to facilitate wire pulling or inspection, especially in long or complex runs. reduce friction, especially for long or complex runs. Ensure the correct conductor sizes and types are used as per the circuit design.
9. Termination and Testing: Terminate wires at appropriate devices (switches, sockets, lights, distribution boards). Perform continuity and insulation resistance tests to ensure the integrity and safety of the installed circuit before energizing. Worked
Example: Installing a PVC Conduit Run for a Simple Light Switch Scenario: A student needs to demonstrate how to run a PVC conduit from a switch box to a lamp holder position on an exposed wall.
Steps:
1. Marking: Measure and mark the desired position for the switch box (e.g., 1.3m from the floor) and the lamp holder (e.g., 2.2m from the floor). Draw a straight line vertically connecting the switch box position to the lamp holder position, indicating the conduit run.
2. Mounting Boxes: Securely fix the PVC switch box and the adaptable box for the lamp holder to the wall using screws and wall plugs. Ensure they are level.
3. Measuring and Cutting Conduit: Measure the exact distance between the two boxes, allowing for penetration into each box. Cut the PVC conduit to this length using a hacksaw, ensuring a clean, straight cut.
4. Fitting Connectors: Insert a PVC conduit connector into one knockout of each box. Secure it with a locknut if the box design requires it.
5. Joining Conduit to Boxes: Apply PVC solvent cement to the end of the conduit and the inside of the connector in the switch box. Push the conduit firmly into the connector. Repeat for the lamp holder box.
6. Fixing Saddles: Place PVC saddles along the conduit run. For a 90cm run, place one saddle in the middle. For longer runs, space saddles every 1.5m, ensuring one is within 30cm of each box. Mark the saddle positions, drill pilot holes, and secure the saddles with screws and wall plugs. Snap the conduit into the saddles.
7. Wire Pulling (Demonstration): Once the conduit is fully installed and secure, push a fish tape from the switch box towards the lamp holder box. Attach the required wires (e.g., Live, Neutral, Earth) to the end of the fish tape. Pull the fish tape back through the conduit, drawing the wires with it.
8. Completion: Trim excess wires, ready for termination into the switch and lamp holder. This practical example illustrates the core process of creating a conduit run, from planning to securing, highlighting the tools and materials involved. Conduit runs refer to the actual path taken by the conduit from one point to another. Proper installation ensures safety, ease of wire pulling, and adherence to electrical codes.
Methods of Conduit Installation:
1. Surface (Exposed)
Wiring: Description: Conduits are installed on the surface of walls, ceilings, or other structures. They are visible.
Advantages: Easy to install, modify, and repair. Good for industrial settings or when aesthetics are not a primary concern.
Disadvantages: Less aesthetically pleasing, can be subject to more physical damage if not strategically placed.
Typical Nigerian Use: Workshops, temporary installations, some commercial buildings, older residential renovations.
2. Recessed (Concealed)
Wiring: Description: Conduits are installed within walls, ceilings, or concrete slabs, making them invisible once the building is finished.
Advantages: Aesthetically pleasing, excellent protection from physical damage.
Disadvantages: More complex and time-consuming to install, difficult to modify or repair, requires careful planning during construction.
Typical Nigerian Use: New residential buildings, modern commercial structures, offices, and schools.
Key Installation Steps and Considerations:
1. Planning and Layout: Review electrical drawings (layout plans showing switch positions, socket outlets, lighting points, distribution board). Mark out the conduit paths on the walls or surfaces according to the approved design. This involves measuring and sketching the exact run for conduits.
2. Material Estimation: Calculate the required lengths of conduit, number of fittings (elbows, couplings, saddles, boxes), and accessories.
3. Cutting Conduits: PVC: Use a hacksaw or PVC conduit cutter for clean, straight cuts.
Metal (EMT/RMC): Use a hacksaw with a fine-tooth blade or a specialized conduit cutter. A reamer is essential to smooth the inside edge of cut metal conduits to prevent wire insulation damage.
4. Bending Conduits: PVC: Heat the bending point evenly using a heat gun until pliable. Insert a bending spring (if available) inside the conduit to prevent kinking, then bend to the desired angle. Allow to cool and harden. Pre-formed bends are also used.
Metal (EMT/RMC): Use a conduit bender tool appropriate for the conduit size. Proper technique is crucial to avoid kinking or flattening the conduit. Avoid excessive bends in a single run (max 360 degrees total between pulling points to ease wire pulling).
5. Joining Conduits and Fittings: PVC: Apply PVC solvent cement to both the outside of the conduit end and the inside of the fitting (coupling, box connector). Insert the conduit firmly into the fitting and give a slight twist to ensure even spread of cement. Hold briefly for initial set.
EMT: Use set-screw or compression fittings. For set-screw, insert conduit and tighten the screws securely. For compression, insert conduit and tighten the compression nut.
RMC/IMC: Thread the conduit ends and screw them into threaded fittings.
6. Fixing Saddles/Clips: Secure saddles to the surface at appropriate intervals to support the conduit. For exposed runs, this is critical for neatness and stability.
Spacing: Typically, support within 30cm of each box or fitting and then every 1.5 to 3 meters along straight runs, depending on local codes and conduit type/size.
7. Mounting Boxes: Fix adaptable boxes (junction, switch, socket boxes) securely at the marked positions. Ensure boxes are level and flush with the finished surface (for concealed wiring).
8. Wire Pulling (Cabling): Once the conduit system is fully installed and secured, electrical wires are pulled through using a fish tape (fishing tape). The fish tape is pushed through the conduit run, hooked onto the wires, and then pulled back, drawing the wires through. Use appropriate wire lubricant (e.g., soapstone powder, specialized pulling gel) to reduce friction, especially for long or complex runs. Ensure the correct conductor sizes and types are used as per the circuit design.
9. Termination and Testing: Terminate wires at appropriate devices (switches, sockets, lights, distribution boards). * Perform continuity and insulation resistance tests to ensure the integrity and safety of the installed circuit before energizing. Worked
Example: Installing a PVC Conduit Run for a Simple Light Switch Scenario: A student needs to demonstrate how to run a PVC conduit from a switch box to a lamp holder position on an
Understanding conduit runs and fittings is highly relevant to various aspects of Nigerian life and economy. Ensuring Electrical Safety in Homes and Public Buildings: Application: In many Nigerian homes, schools, hospitals, and markets, electrical wiring is protected by conduits. This knowledge directly impacts how students perceive and contribute to safe electrical installations. For instance, in a typical Nigerian multi-room residence, PVC conduits are routinely used to embed wiring within walls and concrete slabs, protecting cables from damage, pest infestation, and unauthorized tampering, which are common issues.
Integration: Students can be encouraged to observe conduit installations in their own homes, schools, or local building sites. Discussion can focus on how proper conduit use prevents electrical hazards like short circuits, fires, and electric shocks, crucial for community well-being, especially where exposed or poorly installed wiring is a risk. Economic Opportunities and Skill Development: Application: The ability to properly install conduits is a fundamental skill for electricians and electrical technicians in Nigeria's burgeoning construction sector. From wiring new residential estates in Abuja or Lagos to setting up electrical systems in small businesses or industrial facilities in Kano, conduit installation is a daily task.
Integration: The lesson directly prepares students for vocational training or careers in electrical installation. Teachers can invite local electricians or building contractors to share their experiences and challenges related to conduit work, highlighting the demand for skilled labor in the industry. This connects classroom learning to direct income-generating opportunities and entrepreneurship within Nigeria. Durability and Maintenance in Diverse Environments: Application: Nigeria's diverse climate, from the humid coastal areas to the drier northern regions, presents unique challenges for electrical installations. Conduits offer protection against environmental factors (e.g., moisture in the Niger Delta, dust in the Sahel region). In industrial areas like Port Harcourt or Kaduna, conduits protect cables from corrosive chemicals or mechanical damage from machinery.
Integration: Discuss with students how different conduit materials are chosen based on environmental factors. For example, why RMC might be preferred in a bustling factory near an industrial area over PVC, or why PVC is suitable for most residential applications due to its rust resistance in humid conditions. This emphasizes the critical role of material selection in ensuring the long-term reliability and low maintenance of electrical systems, saving costs and preventing operational downtime.