What cable size do I need? A wiring guide for Ugandan buildings
How to select the correct cable cross-section for mains wiring, sockets, lighting and motor circuits — using Uganda's ambient temperatures and standard conduit practice.
Why cable sizing matters
Under-sized cables overheat, damaging insulation and creating fire risk. Over-sized cables waste money and make terminations difficult. Correct sizing depends on: the current the cable must carry, how the cable is installed, the ambient temperature, and the length of the run.
Standard cable types in Uganda
PVC/PVC flat twin and earth: The most common domestic cable, available in 1.5 mm², 2.5 mm², 4 mm², 6 mm². Used for fixed wiring in conduit or surface trunking.
PVC/SWA/PVC armoured cable: Steel wire armoured — used for underground runs, outdoor exposed wiring, generator feeds. The armour provides physical protection and can serve as earth continuity.
Flexible cord (PVC stranded): Used for appliance leads and extension reels — NOT for fixed wiring.
Aluminium conductor cable: Used by Umeme for service connections. Do not use aluminium inside buildings for branch circuits — terminations corrode rapidly in Uganda's humidity.
Current-carrying capacity (simplified for Uganda)
Uganda's ambient temperature ranges from 22–32°C in most areas. Using IEC 60364 reference method B (in conduit on a wall) and a 30°C ambient correction:
| Cable size | In conduit (A) | Clipped direct (A) | Max circuit length for 3% voltage drop at 16 A |
|---|---|---|---|
| 1.5 mm² | 13 A | 16 A | 17 m |
| 2.5 mm² | 18 A | 25 A | 28 m |
| 4 mm² | 24 A | 34 A | 46 m |
| 6 mm² | 31 A | 43 A | 68 m |
| 10 mm² | 42 A | 60 A | 115 m |
| 16 mm² | 56 A | 80 A | 183 m |
Standard circuit cable sizes
Lighting circuits (protected by 6 A MCB): 1.5 mm² — adequate for up to 13 A load
13 A socket ring main (protected by 32 A MCB in a ring): 2.5 mm² — the ring halves the current each leg carries
Radial socket circuit (20 A MCB): 2.5 mm² up to 20 m, 4 mm² for longer runs
1 HP air conditioner (20 A dedicated circuit): 2.5 mm² up to 25 m from DB
2 HP air conditioner (25 A circuit): 4 mm²
Electric shower (30 A): 6 mm²
Cooker/oven circuit (32–40 A): 6 mm² up to 15 m, 10 mm² for longer runs
Generator feed (63 A from transfer switch to DB): 16 mm² for runs up to 30 m
Voltage drop consideration
For long runs (common in large compounds and commercial buildings), voltage drop becomes the governing factor rather than current capacity. The maximum permissible voltage drop under Uganda wiring regulations (based on BS 7671) is:
- 3% for lighting (7.2 V on 240 V)
- 5% for power circuits (12 V on 240 V)
For a 25 m run at 16 A on 2.5 mm² copper, voltage drop = (25 × 16 × 2) ÷ (56 × 2.5) = 5.7 V = 2.4% — acceptable.
For a 50 m run at the same load, drop doubles to 4.8% — at the limit for power. Upsize to 4 mm² to bring it back to 3%.
Common mistakes to avoid in Uganda
Using sub-standard cable: Many rolls sold in Owino and Kiseka markets are under-gauge (marked 2.5 mm² but measuring 1.8 mm²). Buy cable with a BS or KEBS stamp from a verified supplier and verify cross-section with a micrometer.
Single-core cable in conduit for three-phase: Use three separate single-cores or a proper three-core cable — never two-core plus an added earth buried inside a wall.
Ignoring grouping derating: When 4+ cables run together in the same conduit, the current capacity of each cable must be derated. A bundle of 6 circuits in one conduit may need 50% of the tabulated rating.
No earth continuity: Many older Kampala buildings have no earth wire installed. This is hazardous — any fault makes the entire metalwork live. Always run earth with phase and neutral.