Cable derating calculator

Ask ten people what this figure “should” be and you'll get ten different guesses. The better moment to look at the numbers is now, while changing your mind is still cheap.

There is no account, no paywall and no catch. The more exact your inputs, the more trustworthy the output.

The logic in everyday words

How this calculation applies in Singapore: For Singapore, use the units printed beside each field and do not assume that a familiar name means the same measurement system.

That means the output can be used directly with an accountant, lender or employer in Singapore without converting anything. Cable derating calculation tool turns cable and wire sizes into the right choice — mm² or AWG, current rating, voltage drop, conduit diameter. Between them sits an exact expression. Undersized wire overheats insulation; oversized wire is wasted money.

The calculation in plain English

Over a 30 m three-phase run the voltage drop is around 1.5% — well inside the 3% standard limit. Example: 32 A load on XLPE cable in conduit at 25°C requires a specific mm² cross-section. Use when designing residential or industrial wiring, powering a motor over a long run (voltage drop), on a solar system (panel–inverter link), for audio or network cable over long distance, or converting between European and US specs. AWG to mm² uses S = 0.012668 × 92^((36-AWG)/19.5) × 1000.

Second: ignoring voltage drop on long runs — a motor at 100 m won't begin on undersized wire. For 32 A that's 6 mm² (4 mm² would be marginal).

Using the calculator

• Units of gauge: Fully metric.
• Currency & format: Singapore dollar (SGD, S$).
• Electrical supply: 230 V / 50 Hz, Type G plug (same as UK).
• VAT / sales tax: Singapore's GST is 9% (as of 1 Jan 2024). Financial services and residential rentals are exempt; exports zero-rated.
• Local notes: Numbers use SGD, metric units and IRAS defaults where applicable.

How it works in practice

Overhead runs: add mechanical protection. Always pick with 20–25% margin over computed current.

Solar systems: UV-resistant cable on the DC side. Classic: sizing by nominal current without derating for temperature and install method (at 40°C and bunched cables ampacity drops 30–40%). Third: confusing AWG with mm² (12 AWG ≠ 12 mm², it's 3.31 mm²). For runs longer than 50 m verify voltage drop (max 3% lighting, 5% motors).

Concrete beats abstract every time — see for yourself.

Good times to run the numbers

Typical visitors are users across Singapore's CBD, Jurong and Tampines comparing offers or checking a bill, so the worked examples below use realistic local values rather than abstract numbers. Stranded is more flexible but slightly costlier. Solid — for permanent installs in walls and conduit. Stranded — for movable connections, machinery, extension cords, automotive.

Frequent missteps

Never save on cable — the cost is tiny compared to the risk. Where income, tax or contributions are involved, the reference framework is IRAS and CPF (Central Provident Fund) — personal income tax 0–24%, GST 9%.

For international work every time quote mm² — less confusion. The right cable is the difference between an install that runs 30 years trouble-free and one that overheats under first serious load.

Small habits, better numbers

Every figure above applies to Singapore specifically and is reviewed when the rules change. Singapore's rules are unusually flat and predictable, and Cable derating calculator reflects that structure directly. The values entered here are Base ampacity at 30 °C, 1 cable (A), Ambient temperature (°C), Number of grouped cables.

Keep the original measurement, invoice, specification or log beside the calculation so that a misplaced decimal point can be found.

The bottom line

You're in a stronger position than you were five minutes ago. Change one parameter at a time and watch how the output moves — that's the fastest route to a feel for the maths.