Sq mm Wire Current Capacity Chart

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Check the current capacity of 1.5, 2.5, 4, 6 and 10 sq mm copper or aluminium wire with installation, ambient-temperature and cable-grouping corrections.

Inputs

Cable

Wire cross-section

Conductor material

Installation method

Derating conditions

Ambient temperature

Loaded circuits grouped together

How to use this calculator: Sq mm Wire Current Capacity Chart

Check the current capacity of 1.5, 2.5, 4, 6 and 10 sq mm copper or aluminium wire with installation, ambient-temperature and cable-grouping corrections. The example below is calculated by this page's real engine from the displayed inputs.

1Use the cross-section marked on the cable—such as 1.5, 2.5 or 4 mm². Do not estimate it from the outside diameter because insulation thickness varies.
2Aluminium has higher resistance and normally needs a larger cross-section than copper for the same current and voltage drop.
3Cable in a thermally insulated wall loses heat less effectively than cable in ordinary conduit or clipped directly to a surface, so its permitted current is lower.
4Select the expected ambient temperature and number of loaded circuits that share the conduit, trunking or cable group. Both conditions can substantially reduce ampacity.
5Choose protection so the design load is not above the breaker and the breaker is not above the corrected cable rating. Then use the wire-size calculator for route-length voltage drop.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

Input	Example value	Why it matters
Wire cross-section	2.5 mm²	Select the option that matches the real installation or scenario.
Conductor material	Copper	Select the option that matches the real installation or scenario.
Installation method	In conduit / trunking on or in a wall	Select the option that matches the real installation or scenario.
Ambient temperature	30 °C	Select the option that matches the real installation or scenario.
Loaded circuits grouped together	1 circuit	Select the option that matches the real installation or scenario.

Formula inputs & variables for Sq mm Wire Current Capacity Chart

These are the named quantities used by this calculator. When the source formula does not define a mathematical symbol, OneCalcApp keeps the real input label instead of inventing one.

Variable / input	Unit	Meaning in this calculation
Wire cross-section	—	Select the option that matches the real installation or scenario.
Conductor material	—	Select the option that matches the real installation or scenario.
Installation method	—	Select the option that matches the real installation or scenario.
Ambient temperature	—	Select the option that matches the real installation or scenario.
Loaded circuits grouped together	—	Select the option that matches the real installation or scenario.

Formula, derivation and worked example

Wire size alone does not determine current capacity. The same 2.5 mm² cable can carry a different current when it is surrounded by thermal insulation, enclosed in conduit, clipped in free air, installed in a hot roof space or grouped with other loaded cables. This page starts with an indicative 70 °C PVC cable value and applies the visible correction factors, so the answer is more useful than a single unsupported amps-per-square-millimetre rule.

Corrected capacity Iᶻ = tabulated capacity × material factor × ambient factor × grouping factor

Protective-device check: design load Iᵦ ≤ breaker Iₙ ≤ corrected cable capacity Iᶻ

Substitution steps

1. Reference ampacity
2.5 mm² copper · conduit / trunking
= 23 A
2. Material correction
23 × 1
= 23 A
3. Ambient and grouping
23 × 1 × 1
= 23 A

Computed example results

Corrected current capacity: 23 A; 2.5 mm² copper · conduit / trunking
Base table value: 23 A; copper, 30 °C, before correction
Material factor: 1; Copper
Ambient factor: 1; 30 °C
Grouping factor: 1; 1 circuit group
Largest standard MCB not above capacity: 20 A; preliminary thermal coordination only

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Common mistakes when using Sq mm Wire Current Capacity Chart

Do not copy values into Sq mm Wire Current Capacity Chart without checking that each field represents the quantity described by its label and hint.
Do not leave Wire cross-section on the default choice unless that choice matches the real scenario; the selected option can change the calculation path or factor.
Do not replace the displayed Corrected capacity Iᶻ = tabulated capacity × material factor × ambient factor × grouping factor relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
Do not treat Corrected current capacity = 23 A from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

Next logical calculator

Continue with Wire Size Calculator (AWG & mm²)

Useful next check because both tools use Conductor material, while Wire Size Calculator (AWG & mm²) answers a different part of the same workflow.

Open Wire Size Calculator (AWG & mm²)

Standards, source trail and limitations

References show the method used. Check the current local edition, amendments and project specification before a regulated decision.

PVC vs XLPE insulation and how standards differ

Ampacity depends on how hot the insulation may run. Ordinary 70 °C PVC (IS 694 / IS 1554) cable is the basis of the chart above. XLPE-insulated cable (IS 7098 / IEC 60502) is rated for 90 °C conductor temperature, so the same cross-section carries roughly 15–25% more current when the terminals, accessories and enclosure are also rated for 90 °C — which they often are not in domestic wiring.

The reference standard matters too. IS 732 and IEC 60364-5-52 tables are given per installation method (A1, B1, C, E/F) with 30 °C ambient and 70 °C or 90 °C insulation, while NEC Table 310.16 uses AWG conductors, 30 °C ambient and 60/75/90 °C columns with a separate terminal-temperature limit. A 2.5 mm² PVC value of about 23 A in conduit is therefore not directly comparable to the 12 AWG 75 °C figure of 25 A used in the US.

Why sq mm wire amp ratings vary

A conductor produces I²R heat. Larger copper area reduces resistance, while open air removes heat better than an insulated wall or a crowded conduit. Ambient heat and nearby loaded cables reduce the temperature margin available to the insulation.

Published ampacity charts are therefore tied to a cable type, insulation temperature, number of loaded conductors, ambient temperature and reference installation method. Compare figures only when those assumptions match.

Choosing between 1.5, 2.5 and 4 mm² wire

For normal Indian building wiring, 1.5 mm² copper is commonly used for lighting, 2.5 mm² for socket circuits and 4 mm² for heavier dedicated loads. These are conventions, not automatic approvals: the load, MCB, route length, installation method and voltage drop must agree.

High ambient temperature, several circuits in one conduit, thermal insulation or a long route can push the correct choice one or more standard sizes higher.

MCB coordination and voltage drop

The normal coordination rule is Iᵦ ≤ Iₙ ≤ Iᶻ: design current must not exceed the protective-device rating, and the protective-device rating must not exceed the cable's corrected current capacity. Fault-loop impedance and disconnection time must also be verified.

Ampacity only prevents overheating. A cable can pass the thermal check and still deliver poor voltage at the appliance, especially on long single-phase routes. Always perform the voltage-drop check separately.

Formula

Corrected capacity Iᶻ = tabulated capacity × material factor × ambient factor × grouping factor
Protective-device check: design load Iᵦ ≤ breaker Iₙ ≤ corrected cable capacity Iᶻ

Copper wire current capacity chart — 70 °C PVC, 30 °C ambient

Indicative amperes for two loaded conductors before ambient and grouping correction. Installation details, cable construction, terminals and the applicable manufacturer / IS 732 or IEC 60364 table control the final design.

Size	Insulated wall	Conduit / trunking	Clipped direct	Typical use
1 mm²	10.5 A	13.5 A	15 A	Controls and light-duty wiring
1.5 mm²	13 A	17 A	19.5 A	Lighting circuits
2.5 mm²	17.5 A	23 A	27 A	Socket and small power circuits
4 mm²	23 A	31 A	36 A	Geyser, kitchen and small AC circuits
6 mm²	30 A	40 A	46 A	Larger AC, cooker and sub-main circuits
10 mm²	40 A	54 A	63 A	Sub-mains and distribution feeders
16 mm²	54 A	72 A	85 A	Main feeders
25 mm²	70 A	94 A	112 A	High-current feeders
35 mm²	86 A	115 A	138 A	Industrial feeders

1.5 sq mm wire current capacity

About 17 A for copper in ordinary conduit at 30 °C, before grouping correction. It is commonly protected by a 10 A or 16 A MCB only after the installation method, terminal rating, load and voltage drop have been checked.

2.5 sq mm wire current capacity

About 23 A for copper in ordinary conduit at 30 °C, but approximately 17.5 A inside a thermally insulated wall and 27 A when clipped direct. This is why a universal ‘2.5 mm² = 25 A’ answer can be unsafe.

4 sq mm wire current capacity

About 31 A for copper in ordinary conduit at 30 °C, before heat and grouping correction. A long AC, geyser or kitchen circuit may still need a larger cable because of voltage drop or starting current.

6 and 10 sq mm wire current capacity

About 40 A for 6 mm² and 54 A for 10 mm² copper in ordinary conduit at 30 °C, before heat and grouping correction. These sizes are typical for cooker points, large AC circuits and sub-mains, where voltage drop over a long feeder often decides the size rather than ampacity.

Current capacity is not breaker size

Ampacity is the cable's thermal limit under stated conditions. The MCB must also suit the design load, cable rating, fault protection, appliance instructions and local wiring rules.

Wire Size Calculator

Choose a conductor from current, route length and allowable voltage drop.

Wire Gauge Chart

Convert AWG to mm² and compare diameter, resistance and typical ampacity.

Assumptions

Base figures represent indicative 70 °C PVC insulated copper cable with two loaded conductors at 30 °C ambient.
Aluminium capacity is estimated at 78% of the same-size copper value; use the actual manufacturer table for final design.
Correction factors are applied independently and multiplied together.

Warnings

Do not select a cable or MCB from cross-section alone; verify the cable datasheet and the installation table applicable to the project.
Motor, compressor and transformer circuits require starting-current, protection and short-circuit checks in addition to steady current.
Electrical installation and modification should be carried out and verified by a qualified person.

Standards & references

IS 732:2019
IEC 60364-5-52
IEC 60228

Frequently asked questions

How many amps can 2.5 sq mm copper wire carry?

An indicative value is about 23 A in ordinary conduit at 30 °C. It can be around 17.5 A in a thermally insulated wall or 27 A clipped direct, before ambient and grouping corrections.

How many amps can 1.5 sq mm copper wire carry?

About 17 A in ordinary conduit at 30 °C is a useful reference value. Heat, grouping, thermal insulation, terminal ratings and the cable manufacturer's table can reduce it.

How many amps can 4 sq mm copper wire carry?

About 31 A in ordinary conduit at 30 °C, approximately 23 A in a thermally insulated wall and 36 A clipped direct, before correction factors.

Can I use 2.5 sq mm wire with a 25 A MCB?

Not automatically. A 25 A MCB is above the indicative 23 A conduit rating and can be unsuitable after heat or grouping derating. Verify the exact cable table and keep Iᵦ ≤ Iₙ ≤ Iᶻ.

Is aluminium wire rated the same as copper?

No. Aluminium has higher resistance and lower current capacity for the same cross-section, so it normally requires a larger size and aluminium-rated terminals.

What inputs does the Sq mm Wire Current Capacity Chart use?

It uses Wire cross-section, Conductor material, Installation method, Ambient temperature, and Loaded circuits grouped together. Follow the unit printed for each field and choose any selectable option to match the real scenario.

What does the Sq mm Wire Current Capacity Chart calculate?

It calculates Corrected current capacity, Base table value, Material factor, Ambient factor, Grouping factor, and Largest standard MCB not above capacity. With the displayed default inputs, Corrected current capacity is 23 A.

Which formula does the Sq mm Wire Current Capacity Chart use?

The primary relationship is Corrected capacity Iᶻ = tabulated capacity × material factor × ambient factor × grouping factor. The page also shows substituted values and calculation steps so the result can be checked independently.

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