Incorrect Cable Sizing Increases Energy Costs

What is Cable Sizing and Why It Matters?

Cable sizing is the process of selecting the correct conductor size for a given electrical load, installation method, and cable run distance. Every cable has a rated current carrying capacity. When that limit is exceeded, the cable heats up. When it heats up repeatedly and excessively, the insulation begins to fail.

A proper cable sizing calculation considers several critical factors. These include the load demand measured in amperes, the total length of the cable run, the installation conditions such as conduit, cable tray, or direct burial, the ambient temperature of the installation environment, and the permitted voltage drop across the circuit.

When these factors are ignored, the system may appear to function at first. However, it will operate inefficiently from the outset and deteriorate progressively over time.

How Incorrect Cable Sizing Increases Energy Costs?

When a cable is undersized, its electrical resistance is higher than it should be for the load it carries. Higher resistance means more energy is lost as heat during operation rather than being delivered to the connected equipment.

This is governed by a fundamental electrical principle known as Joule heating. The power lost in a conductor increases with both the current flowing through it and the resistance of the conductor itself. When resistance rises due to under-sizing, energy loss increases rapidly.

A Practical example

Consider a single-phase load of 5 kW supplied at 230 V, with a cable run of 30 metres one way, giving a total loop length of 60 metres. Two cable sizes are compared: a 1.5 mm² copper cable and a 2.5 mm² copper cable.

Step 1: Calculate the Load Current

Using the basic power relation, the load current is calculated as follows.

Current equals power divided by voltage. At 5,000 watts and 230 volts, the current is approximately 21.7 amperes.

Step 2: Cable Resistance Values

Typical resistance values for copper cable are 12.1 ohms per kilometre for 1.5 mm² and 7.41 ohms per kilometre for 2.5 mm². Over 60 metres, the resistance values are as follows.

• 1.5 mm² cable: 12.1 × 0.06 = 0.726 ohms
• 2.5 mm² cable: 7.41 × 0.06 = 0.445 ohms

Step 3: Calculate Power Loss

Applying the Joule heating formula, where power loss equals current squared multiplied by resistance, the losses are as follows.

• 1.5 mm² cable: (21.7)² × 0.726 = approximately 342 watts lost
• 2.5 mm² cable: (21.7)² × 0.445 = approximately 209 watts lost

Step 4: The Real Cost of That Difference

The smaller cable wastes an additional 133 watts continuously compared to the correctly sized cable. Assuming the load operates for 10 hours per day, the extra energy wasted amounts to 1.33 kilowatt-hours per day and approximately 39.9 kilowatt-hours per month.

At an electricity cost of $1.50 per kilowatt-hour, this represents a monthly waste of approximately $60 on a single circuit alone.

In a commercial or industrial building with multiple circuits, the cumulative financial loss becomes substantial. A single design error, repeated across an entire installation, can cost thousands of dollars in wasted energy every year.

The Science Behind Overheating

When electrical current flows through a conductor, heat is produced. In a correctly sized cable, that heat remains within safe operating limits and dissipates safely into the surrounding environment. In an undersized cable, heat builds up faster than it can dissipate.

This creates a dangerous self-reinforcing cycle. The cable heats up, which causes its resistance to increase further, which generates more heat, which raises resistance again. Each stage of this cycle accelerates the next. Eventually, the insulation surrounding the conductors begins to break down. Once insulation fails, the risk of fire increases dramatically.

How Overheating Leads to Fire

Heat alone does not cause immediate failure. The danger develops gradually through a series of identifiable stages, each more serious than the last.

Insulation Degradation

Sustained high temperatures weaken cable insulation. It becomes brittle, loses its elasticity, and begins to crack. Once cracked, it no longer provides reliable protection against electrical contact between conductors or between conductors and surrounding materials.

Loose Connections

Repeated cycles of thermal expansion and contraction loosen terminal connections over time. Loose connections create localised hotspots where resistance is concentrated and heat is most intense.

Arcing

Damaged insulation and loose terminal joints create conditions for electrical arcing. Arcing produces intense, localised heat and generates sparks capable of igniting surrounding materials.

Fire Ignition

Wood, dust, insulation foam, and plastics commonly found inside walls and ceilings will ignite when exposed to arcing or sustained extreme heat. Because these fires start inside concealed spaces, they are frequently well established before they are detected.

Common Cable Sizing Mistakes

In many projects, cable sizing errors happen due to avoidable reasons.

1. Cost cutting
   Some installers use smaller cables to reduce material cost. This creates long term losses and safety risks.
2. Lack of load calculation
   Without proper load estimation, cable selection becomes guesswork.
3. Ignoring voltage drop
   Long cable runs require larger sizes. Ignoring this leads to poor performance.
4. Poor workmanship
   Untrained technicians may not follow standards
5. Non-compliance with regulations
   Guidelines from Energy Commission Ghana are often ignored.

These mistakes are common in both residential and commercial buildings.

Warning Signs You Should Not Ignore

You can detect cable sizing problems early if you know what to look for.

• Frequent tripping of circuit breakers
• Warm or hot cables and sockets
• Burning smell from outlets
• Flickering or dim lights
• Reduced performance of equipment

If you notice any of these signs, you should act immediately. Delays increase the risk of damage or fire.

Real-World Scenario

A small commercial shop in Accra installed air conditioners and refrigeration units. The original wiring used 1.5 mm² cables designed only for lighting loads.

After upgrading equipment:

• The cables began to overheat
• Voltage dropped significantly
• Breakers tripped frequently

Within months, insulation near a junction box melted. This nearly caused a fire.

After replacing the cables with correctly sized conductors:

• Power stabilised
• Energy loss reduced
• Equipment performed efficiently

This shows how a simple design error can create serious problems.

How to Prevent Cable Sizing Problems

Preventing incorrect cable sizing requires professional planning and qualified execution at every stage of an electrical project.

1. Perform Accurate Load Calculations

Every connected load must be assessed, including allowance for future expansion. Accurate load data is the foundation of every correct cable sizing decision.

2. Follow Recognised Standards

Cable selection must comply with recognised electrical installation standards and the regulations of the Energy Commission of Ghana or electrical installation standards and the regulations 

3. Account for Installation Conditions

Heat dissipation varies significantly depending on how a cable is installed. Cables in conduit, cables bundled together, and cables installed in high ambient temperatures all require derating to account for reduced heat dissipation.

4. Factor in Voltage Drop

Long cable runs require larger conductors than the load calculation alone would suggest. Voltage drop calculations must be performed for every circuit of significant length.

5. Hire Qualified and Certified Electricians

Only licensed and certified electrical engineers with experience in system design should be entrusted with cable sizing decisions. The cost of professional expertise is a fraction of the cost of getting it wrong.

6. Carry Out Regular Inspections

Periodic inspection of electrical installations detects developing problems before they become dangerous. Regular testing of insulation resistance, connection integrity, and circuit performance provides early warning of deterioration.

Why This Matters for Building Owners and Businesses

Incorrect cable sizing affects far more than electrical safety. It directly and measurably impacts the finances and operational continuity of every business and property it affects.

The consequences include increased electricity bills that persist for as long as the undersized cables remain in place, frequent and premature equipment failure caused by voltage irregularities, unplanned operational downtime, and high maintenance costs that compound over time. In industrial settings, even a modest inefficiency translates directly into reduced productivity and increased operating costs.

Correct cable sizing is a one-time investment. The return on that investment is measured in years of reliable, efficient, and safe electrical operation.

Mega Solution Electrical Engineering: Expert Cable Sizing and Electrical Design

At Mega Solution Electrical Engineering, our licensed and certified electrical engineers conduct detailed load assessments, apply recognised cable sizing standards, and verify every installation through testing and commissioning before handover. We work across residential, commercial, and industrial projects throughout Ghana, and we approach every contract with the same commitment to safety, efficiency, and technical precision.

If you suspect cable sizing issues in your installation, or if you are planning a new electrical project and want it done correctly from the outset, contact Mega Solution Electrical Engineering today for a professional assessment and quotation.

Final Thoughts

• Cable sizing is not a minor detail. It is a critical part of electrical design. When done incorrectly, it leads to energy waste and serious fire risks.
• If you want a reliable system, you must prioritise correct sizing, proper installation, and compliance with standards.
• If you suspect issues in your installation or want a professional assessment, contact us for a quote.