What is it?

Electrical installation design is the planning and design stage that has to be carried out before any electrical work can be done. It involves the selection of cables, circuit breakers, fuses and other accessories such as switches, sockets etc. Essentially, it is the first stage of electrical work. As an analogy, conducting electrical design is similar to purchasing a map and marking out locations for a road trip- without it you don’t know how to get to your destination! Extending the analogy, with electrical installations, the ‘destination’ is a safe and usable electrical installation. 

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Why should you do it?

To put it simply- for your own safety! To protect yourself and the users and occupiers of any home, office or factory. With the use of electricity in our daily lives being widespread, and of paramount importance to a 21st century economy, it must be recognised that the use of electricity is not without its risks. 

 

The two major risks of electricity are electrocution (death by electric shock) and fires. To ensure users of an electrical installation are safeguarded from these risks, electrical installation design has to be carried out in accordance with a standard for electrical installations. In India, this is the National Electrical Code of India (SP 30), which has been adopted from the international standard IEC 60364, which is also adopted by most countries across the world.

 

Conducting electrical installation design, and by extension complying with SP 30 ensures that “persons, livestock and property” are protected against the “dangers and damage which may arise in the reasonable use of electrical installations”. To put it simply, ensuring compliance with SP 30 protects people and property from electrical shock, and fire (among other hazards such as power surges) in homes, offices and factories.

 

In India, you are also legally required to carry out electrical installation design. The Central Electricity Authority (Measures Relating to Safety and Electric Supply) Regulations 2023 requires electrical installations to comply with the National Electrical Code of India (SP 30), which requires electrical installations to be designed before they are constructed (erected). 

 

Legality aside, a design specification ensures safety and peace of mind for you as a user of an electrical installation!

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When should you do it?

Whenever electrical work is carried out, there are three distinct stages to it:

 

1. Design: Planning and specifying the components, layout, and configuration of an electrical installation.

2. Erection: Physical construction of the designed system. This is what most people think of when they think of electrical work.

3. Verification: Inspecting and testing the electrical installation to ensure erection is carried out as intended by the design.

 

As observed, design is the first stage! This means whenever any electrical work needs to be carried out, the first thing that must be done is electrical installation design. Without design, a safe electric installation is very difficult to erect. Notably, no project is too small for electrical design to be carried out- whether it is a one-bedroom apartment, or a massive datacentre, electrical installation design in each of these premises is a must.

 

Often, electrical work is carried out as part of a larger project, such as building a house, or renovating an apartment. In such cases, electrical installation design needs to be carried out once architectural plans have been finalised and before any construction/renovation work starts.

 

What do you get from it (deliverables)?

After the completion of electrical installation design, the end result is a set of documents called a ‘design specification’. It consists of all the necessary information for a licensed electrical contractor (LEC) to construct (erect) a safe electrical installation. A design specification includes:

 

1. 2D CAD Plan: shows wiring routes on floorplan (top view).

2. Circuits Schedule: shows for every circuit, the estimated load current (including the effects of power factor, diversity and triplen harmonics), specified circuit protective devices (Including nominal current, type of device, and settings) and specified conductor (including type and length).

3. Calculations Overview: shows for every circuit, calculations for- current carrying capacity, breaking capacity, L-N fault thermal withstand, L-PE fault thermal withstand and earth fault loop impedance.

4. Voltage Drop Analysis: shows for every circuit, the voltage drop for the estimated load current on the specified conductor including the effect of power factor, resistive voltage drop and reactive voltage drop. Also shows the split between voltage drop on the supply and individual circuit.

5. Analytical Calculations Report: shows for every circuit, circuit design data (including conductor type, installation method, cpc details, protective device details), circuit calculations (including current carrying capacity at continuous service and for disconnection under single fault conditions).

6. Earth Fault Loop Impedance Report: shows for every circuit, the earth fault loop impedance value at the circuit extremity (including maximum allowable R1+R2 values).

7. Circuit schematic: shows the distribution structure of the electrical installation from incomer to distribution boards to final circuits.

8. Cable schedule: shows for every circuit, the cable type and cross-sectional area specified, along with length, reference methods, incomer and load details.

9. Protective devices schedule: shows for every circuit, the specified protective device, and settings.

10. Accessories Report: a list of required accessories with part numbers for the erection of the electrical installation. Includes lugs, terminal blocks, cleats, glands, etc. 

11. Switch and Socket Wiring Diagram: drawings showing the required connections for socket-outlets and lighting switching arrangements. 

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