Day 16 Night – ECET 2026 EEE: Estimation → Industrial Wiring

A lite explanation of why this topic is important for ECET

Industrial wiring is a practical backbone of electrical engineering. Whether it’s a factory, workshop, or plant, safe and efficient wiring ensures smooth operation of motors, machines, and heavy loads. For ECET 2026 aspirants, questions on estimation and wiring test basic design skills, safety awareness, and numerical ability. Mastering this topic helps you not only in exams but also in future as an electrical engineer.

📘 Concept Notes

1. What is Industrial Wiring?

Industrial wiring refers to the system of distributing electrical energy in workshops, factories, and large buildings where the load is mostly 3-phase and heavy-duty. It includes:

Motor control circuits
Lighting loads
Power sockets
Protection devices

2. Types of Wiring Systems Used in Industry

Conduit wiring (surface or concealed): Strong, safe, suitable for heavy loads.
Busbar trunking system: For large current distribution.
Cable tray system: For organizing multiple power/control cables.

3. Factors Considered in Estimation

Load calculation: Total connected load of motors, lights, sockets.
Diversity factor (DF): Not all loads work at the same time.

$P_{max} = \frac{P_{total}}{DF}$

Current calculation:

$I = \frac{P}{\sqrt{3} \cdot V \cdot \cos\phi}$

Size of conductor: Selected based on current carrying capacity & voltage drop.

Protective devices: MCBs, fuses, ELCB, MCCB.

4. Estimation Procedure

Prepare single-line diagram of the system.
List out all loads (motors, lighting, etc.).
Calculate total connected load and maximum demand.
Determine conductor sizes and protective devices.
Estimate cost of materials + labor.

5. Examples

Example 1:
A 10 HP motor is to be installed in a factory. Find full load current if supply is 415 V, 3-phase, $\cos\phi = 0.8$ , efficiency = 90%.

$P = 10 \times 746 = 7460 \ W$
$P_{in} = \frac{7460}{0.9} = 8289 \ W$

$I = \frac{P_{in}}{\sqrt{3} \times V \times \cos\phi} = \frac{8289}{\sqrt{3}\times 415 \times 0.8} \approx 14.4 \ A$

So, conductor size must be chosen for 14.4 A.

⚙️ Formulas

Power (3-phase): $P = \sqrt{3} \cdot V \cdot I \cdot \cos\phi$
Current: $I = \frac{P}{\sqrt{3} \cdot V \cdot \cos\phi}$
Maximum Demand: $P_{max} = \frac{P_{total}}{DF}$
Motor Output Power: $P_{out} = HP \times 746$
Input Power: $P_{in} = \frac{P_{out}}{\eta}$
Conductor selection: Based on $I \geq I_{calculated}$ and voltage drop limits.

🔟 10 MCQs

Q1. In industrial wiring, the most preferred method for heavy load distribution is:
a) Wooden casing capping
b) Conduit system
c) Cleat wiring
d) Batten wiring

Q2. A 5 HP motor (415V, 3-phase, $\cos\phi = 0.85$ , efficiency 90%) draws how much current?
a) 5.6 A
b) 7.9 A
c) 8.9 A
d) 10.2 A

Q3. Diversity factor is always:
a) < 1
b) > 1
c) Equal to 1
d) Zero

Q4. Maximum demand of a system is calculated as:
a) $P_{max} = P_{total} \times DF$
b) $P_{max} = \frac{P_{total}}{DF}$
c) $P_{max} = P_{total}$
d) None

Q5. For industrial wiring, busbar trunking is used for:
a) Controlling lights
b) Small residential circuits
c) Distributing large currents safely
d) Reducing conductor size

Q6. The input power of a 7.5 HP motor (efficiency = 0.9) is:
a) 5600 W
b) 7460 W
c) 6220 W
d) 6210 W

Q7. Protective device used for earth leakage in industry is:
a) MCB
b) MCCB
c) ELCB
d) Fuse

Q8. A 20 kW, 3-phase load at 0.8 PF is supplied by 415 V. Find the line current.
a) 27.8 A
b) 34.7 A
c) 40.2 A
d) 45.6 A

Q9. Conductor size for industrial wiring is selected based on:
a) Current carrying capacity
b) Voltage drop limit
c) Both (a) and (b)
d) Only cost factor

Q10. In estimation, the first step is:
a) Costing
b) Drawing single line diagram
c) Load calculation
d) Cable tray selection

✅ Answer Key

Q.No	Answer
1	b
2	c
3	b
4	b
5	c
6	d
7	c
8	b
9	c
10	b

🧠 Explanations

Q1: Conduit system is safest and suitable for heavy industrial loads → (b).
Q2: $P_{out} = 5 \times 746 = 3730 W$ , $P_{in} = 3730/0.9 = 4144 W$ , $I = \frac{4144}{\sqrt{3} \times 415 \times 0.85} \approx 8.9 A$ → (c).
Q3: Diversity factor is always >1 → (b).
Q4: Formula → $P_{max} = \frac{P_{total}}{DF}$ → (b).
Q5: Busbar trunking is for safe large current distribution → (c).
Q6: $P_{out} = 7.5 \times 746 = 5595 W$ , $P_{in} = 5595/0.9 \approx 6217 W$ → (d).
Q7: ELCB is used for earth leakage protection → (c).
Q8: $I = \frac{20000}{\sqrt{3} \times 415 \times 0.8} = 34.7 A$ → (b).
Q9: Both current capacity & voltage drop matter → (c).
Q10: First step is preparing SLD (Single Line Diagram) → (b).

🎯 Motivation / Why Practice Matters

Industrial wiring problems test your speed of calculation and accuracy in estimation. In ECET 2026, expect direct numericals on load current, power, and diversity factor. Practicing these regularly gives you an edge over others, as many students ignore estimation topics but they carry sure-shot scoring marks.

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Day 16 Night – ECET 2026 EEE: Estimation → Industrial Wiring

A lite explanation of why this topic is important for ECET