Key takeaways
- Start from a load list with diversity to find maximum demand before sizing anything.
- LT panels should be specified for current rating, fault level, form of separation and selectivity.
- Cables are sized for current with derating, voltage drop and short-circuit withstand.
- Earthing, power factor correction, DG integration and testing are part of the design, not add-ons.
A factory’s electrical system has to run motors, heaters, compressors, lighting and controls reliably for decades, often while the plant grows around it. Many of the problems plants live with, such as nuisance tripping, overheating cables, low power factor penalties and unsafe earthing, trace back to decisions made before installation began. This guide walks through the planning of an industrial electrical installation.
1. Start with a load list and maximum demand
Every design begins with a list of connected loads: each machine, motor, heater, HVAC unit, compressor and lighting circuit, with its rating. Not all loads run at full output at the same time, so diversity and utilisation factors are applied to estimate the maximum demand.
Maximum demand drives the sanctioned load or contract demand you apply for, the transformer size for HT consumers, and the rating of the main incomer. It is also worth allowing sensibly for planned expansion, because replacing a main panel later is far more disruptive than sizing it correctly now.
2. Plan the distribution architecture
A typical industrial distribution system runs:
- Utility supply, and for HT consumers, the HT switchgear and transformer
- The main LT panel, often called the power control centre (PCC)
- Motor control centres (MCCs) for groups of motors
- Sub-distribution boards for production areas, utilities, lighting and offices
- Final circuits to equipment
For high currents over longer distances, busducts are often neater and more flexible than parallel cable runs. Locate panels close to their loads where possible, to keep cable lengths and voltage drop down.
3. Specify LT panels properly
An LT panel specification should cover more than a list of breakers:
- Rated current of busbars and incomers, allowing for ambient temperature inside the enclosure
- Short-circuit rating in kA, matched to the fault level available at that point in the system
- Form of separation, from Form 1 to Form 4, which determines how far compartments are segregated and whether one feeder can be worked on while others stay live
- Protective devices: air circuit breakers for large incomers and moulded case circuit breakers for feeders, with suitable releases
- Selectivity, so a fault on one feeder trips only its own breaker instead of the upstream incomer
- Standards: low-voltage switchgear assemblies should be designed and verified to IS/IEC 61439
- Metering, indication, cable entry and space for future feeders
4. Size cables for more than current
Cables are selected on three checks, and the largest size required by any of them governs:
- Current-carrying capacity, after derating for grouping on trays, ambient temperature and installation method
- Voltage drop over the run, which matters most for long feeders and motor starting
- Short-circuit withstand, so the cable survives a fault until the protective device clears it
XLPE-insulated armoured cables are common for industrial power distribution. Route power and control cables on separate trays or with adequate separation, and support and label them properly so they can be traced later.
5. Correct power factor
Induction motors, welding machines and transformers draw reactive power, lowering power factor. Many Indian distribution companies bill on apparent energy (kVAh) or penalise low power factor, so poor power factor translates directly into cost.
Automatic power factor correction (APFC) panels switch capacitor banks in and out to keep power factor close to unity as the load changes. Where variable frequency drives and other non-linear loads create harmonics, detuned reactors are used with the capacitors to prevent resonance and capacitor failure.
6. Design earthing and lightning protection
Earthing protects people from electric shock and allows protective devices to operate when a fault occurs. A good design covers system earthing, equipment earthing of every metallic enclosure and structure, earth pits sized for the expected fault current, and bonding of pipework and structural steel. The Indian code of practice for earthing is IS 3043.
Earth resistance should be measured at installation and periodically after, since pit condition changes with soil moisture. Lightning protection for buildings is designed to IS/IEC 62305 based on a risk assessment.
7. Integrate DG sets and solar
- AMF panels start the generator and transfer the load automatically on mains failure.
- Synchronising panels allow multiple generators to share load.
- Interlocks must prevent the generator and grid supply from being connected in parallel unless designed to do so.
- Rooftop solar needs controls to prevent reverse power flow into DG sets, as explained in our guide to on-grid solar for factories.
8. Choose motor starting methods
Direct-on-line starting is simple but draws a high inrush current. Star-delta starters, soft starters and variable frequency drives reduce starting current. VFDs also save substantial energy on pumps and fans that do not need to run at full speed, which often pays for the drive.
9. Test before energising
- Insulation resistance testing of cables and equipment
- Continuity of protective conductors
- Earth resistance measurement
- Verification of breaker and relay settings and operation
- Phase sequence and polarity checks
- Thermographic inspection of panels once they are under load
10. Safety regulations and approvals
Electrical installations in India are governed by the Central Electricity Authority’s safety regulations, currently the CEA (Measures relating to Safety and Electric Supply) Regulations, 2023, together with state rules. Installations above specified voltage or capacity thresholds require inspection or approval before energisation. Your electrical contractor should identify which approvals apply and prepare the documentation.
Planning checklist
- Complete load list with ratings, operating hours and future expansion
- Maximum demand calculation and supply capacity
- Single line diagram approved before panel manufacture
- Fault level study and protective device coordination
- Cable schedule with sizing calculations
- Power factor correction and harmonic assessment
- Earthing and lightning protection design
- DG and solar integration scheme
- Testing plan and approvals list
1 Worldcrafts provides industrial and commercial electrical contracting, from LT panels and cabling to earthing, testing and commissioning, alongside HVAC and fire fighting systems. Talk to our engineers about your plant.
Frequently asked questions
A power control centre (PCC) is the main LT distribution panel that receives the incoming supply and distributes power to downstream panels. A motor control centre (MCC) groups the starters, protection and controls for a set of motors, such as those in a production line or utility plant room.
If your plant has significant motor or inductive loads and your distribution company bills on kVAh or penalises low power factor, an APFC panel usually pays for itself quickly. Where VFDs or other non-linear loads are present, a detuned APFC panel should be used.
Earth resistance should be measured at installation and then periodically, commonly at least once a year, with dry-season readings giving the most conservative values. Any modification to the installation is also a good reason to re-test.
Form of separation describes how the inside of a switchgear assembly is divided. Form 4 provides the highest segregation, separating busbars, functional units and their terminals, so an individual feeder can be isolated and worked on with less risk while the rest of the panel remains in service.
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