Electrical Systems

Electrical Systems

  • 1. Introduction
  • SpecX quick selector
  • 2. Applicable Codes & Standards
  • 3. Classification of Electrical Systems
  • 4. Key System Components
  • 5. Design Parameters
  • 6. QA/QC Checklist (Sample)
  • 7. Typical BOQ Line Items

1. Introduction

  • Electrical systems are responsible for safe and reliable power distribution across residential, commercial, and industrial facilities.
  • The design aims to ensure uninterrupted supply, safety, energy efficiency, and compliance with Indian and international codes (IS, IEC, NBC).
  • Components include power supply and distribution, lighting systems, earthing and lightning protection, cabling and wiring, control panels and automation.

SpecX quick selector

  • LV distribution: 11 kV/415 V transformer (oil/dry) → LT panel → SMDB → DB; PF ≥ 0.95; short‑circuit withstand as per fault study
  • Cables: XLPE armored FRLS for risers; voltage drop < 2.5% lighting, < 5% power; follow IS 1255 laying practices
  • Earthing: Dual earth pits per transformer/panel; main earth ≤ 1 Ω; equipment earth ≤ 2 Ω; GI/Cu as per IS 3043
  • Lighting: LED with occupancy/daylight controls; offices 300–500 lux; emergency lighting on UPS/central battery

2. Applicable Codes & Standards

Standard
Description
IS 732:2019
Code of practice for electrical wiring installations
IS 3043:2018
Earthing and grounding
IS 1646
Fire safety in electrical installations
IS 5578 / IS 11353
Cable marking and identification
IS 1255
Installation and maintenance of power cables
IEC 60364
Electrical installations for buildings
NBC 2016 – Part 8
Building services – Electrical and allied installations

3. Classification of Electrical Systems

Category
Description
Typical Components
Low Voltage (LV)
≤ 1,000 V — lighting, small power, motors
Switchboards, MCCs, wiring, sockets
Medium Voltage (MV)
1 kV–33 kV — industrial and commercial supply
Transformers, RMUs, ring feeders
High Voltage (HV)
> 33 kV — grid and utility level
Substations, transmission lines
ELV (Extra Low Voltage)
Communication and control
CCTV, fire alarm, BMS, networking

4. Key System Components

Component
Description
Transformers
Step‑down from 11 kV to 415 V, oil/dry type, tested as per IS 1180
Switchgear
MCCB, ACB, VCB — protection and isolation
Cables
XLPE/Armoured/FRLS, laid as per IS 1554 / IS 7098
Earthing System
GI/Copper electrode, plate or chemical type earthing
Lighting System
LED luminaires, occupancy sensors, daylight integration
Panels & Distribution Boards
LT Panels, PDBs, SMDBs, DBs as per IS 8623
Bus Ducts
Large current distribution (1000–6000 A)
Fire Detection & ELV
Fire alarm, access control, CCTV, PA system

5. Design Parameters

  • Voltage drop: < 2.5% for lighting, < 5% for power
  • Power factor: ≥ 0.95 lagging
  • Short‑circuit withstand: Rated as per system fault level
  • Lighting levels (lux): Offices 300–500; Industrial 200–750; Residential 100–200
  • Earthing resistance: ≤ 1 Ω (main), ≤ 2 Ω (equipment)

6. QA/QC Checklist (Sample)

Inspection Item
Frequency
Acceptance Criteria
Verify cable size and insulation
Before installation
As per drawings, no damage
Earth pit testing
Commissioning
≤ 1 Ω resistance
Panel phase sequence check
Pre‑energization
Correct phase and labeling
Lighting circuit testing
Final
No short/open circuit
Insulation resistance test
Pre‑commissioning
≥ 1 MΩ (500 V megger)

7. Typical BOQ Line Items

Item No.
Description
Unit
Measurement Rule
1
Supply and laying of 4C × 16 sq.mm XLPE armored cable
Rm
Per running meter
2
Supply and installation of 250 A LT panel
Nos
Per complete set installed
3
Point wiring with 2.5 sq.mm copper FRLS wire with modular switch
Nos
Per point
4
Earthing pit with GI plate, chamber, salt, charcoal complete
Nos
Per pit completed
⚠️

Common failures (quick scan)

  • Nuisance tripping → incorrect breaker curves or selective coordination; review settings and discrimination
  • Hot spots on cables/panels → undersizing or loose terminations; thermography and re‑torque
  • High earth resistance → dry soil/poor bonding; improve moisture/parallel electrodes, verify bonds
  • Excess voltage drop → long runs/undersized cables; re‑route or upsize conductors
  • EMC/ELV noise → poor segregation/screening; separate ELV and power, use shielded cables