Choosing the wrong cable size is one of the most common — and most dangerous — mistakes on an electrical project. This guide covers the core factors that determine correct cable sizing for a UAE installation.
Why Cable Sizing Matters
An undersized cable overheats under load, creating a genuine fire risk and premature insulation failure. An oversized cable is safe but wastes money unnecessarily. Correct sizing balances safety, compliance, and cost.
The Core Factors in Cable Sizing
- Current rating (ampacity): the cable must safely carry the maximum expected load current.
- Voltage drop: longer cable runs need a larger cross-section to keep voltage drop within acceptable limits.
- Installation method: cables in conduit, buried, or in free air are each rated differently for the same size.
- Ambient temperature: UAE's high ambient temperatures reduce a cable's safe current-carrying capacity compared to cooler climates — an important local consideration.
- Grouping: multiple cables bundled together derate each other's safe current capacity.
A Simplified Sizing Process
- Calculate the actual load current the cable will carry.
- Determine the cable run length for voltage-drop calculation.
- Identify the installation method and any grouping with other cables.
- Factor in UAE ambient temperature derating.
- Select a cable size that satisfies both current-carrying capacity and voltage-drop limits.
Common Cable Sizing Mistakes
The most frequent error is sizing purely on load current while ignoring voltage drop on longer runs — a cable can be technically rated for the current but still cause unacceptable voltage drop over distance, leading to poor equipment performance at the far end of the circuit.
Why UAE's Climate Matters
High ambient temperatures common across UAE installations reduce a cable's safe current rating compared to temperate-climate tables — always apply the correct temperature derating factor rather than relying on standard ratings alone.
Frequently Asked Questions
Can I use the same cable size regardless of run length?
No — voltage drop increases with length, so longer runs often need a larger cable size even for the same load current.
Does cable size affect circuit breaker selection?
Yes — the breaker must protect the cable's rated capacity, so the two are always sized together.
Should I always size cables generously to be safe?
Within reason — moderate oversizing is safe but unnecessarily costly; correct calculation is the better approach.
Shop Genuine Cable and Circuit Protection
Electrical Market stocks genuine cable, MCBs, MCCBs, and isolators from Schneider, ABB, Legrand, and Hager with fast UAE delivery. Call +971 56 619 6379 or WhatsApp us for technical guidance on your project.