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An online calculator tool known as the cable size calculator is mainly intended for use by electrical engineers, electricians and electrical contractors. 

Its primary purpose is to enable these professionals to identify and properly estimate the necessary cable sizes for three-phase motor installations in a short amount of time. 

The calculator supports both the Direct on Line (DOL) and Star Delta starter configurations for the electric motors ranging from 0.37 kW to 143 kW.

Purpose

• Simplify the cable selection for motor installations.

• Ensure the safety compliance with electrical standards.

• Reduce the design time with an instant calculations.

• Support the dual starter types (DOL and Star Delta).

• Provide aluminum and copper options for the cable sizes.

Features

1). Motor Selection

With 24 standard motor ratings ranging from 0.37 kW to 143 kW.

Specifications expressed in kW/HP.

Auto-filled specifications for the electrical setup.

A pick from a dropdown menu for easy access.

2). Automatic Calculations

Line Current 

Full load current at supply.

Phase Current

Phase-wise current distribution.

Fuse Ratings

Calculated at 1.5 x multiplier.

Cable Sizes

Both aluminum and copper options.

3). Dual Starter Support

DOL (Direct On Line)

At starting, the current is at its maximum.

Direct connection to the supply system.

Maximum Fuse Current: 125 Amps.

Range of Overload: 50-90 Amperes

Star Delta

Reduced starting current which is equal to one-third (1/√3 ) of the line current.

During the starting step, motor is protected.

Fuse maximum: 100 A.

38–63 Amperes is the overload range.

Technical Specifications

Electrical Standards

Voltage: 415V, 3-Phase.

Frequency: 50 Hz

Fuse Multiplier: 1.5x full load current.

Safety Factor: Built-in overcurrent protection.

Supported Cable Sizes – Aluminum

S.No	Cable Size (mm²)
1	2.5
2	4
3	6
4	10
5	16
6	25
7	35
8	50
9	70
10	95
11	120
12	150

Supported Cable Sizes – Copper

S.No	Cable Size (mm²)
1	1.5
2	2.5
3	4
4	6
5	10
6	16
7	25
8	35
9	50
10	70
11	95
12	120

Motor Database

The calculator includes 24 standard motor ratings:

S.No	kW	HP	Line Current (A)	Phase Current (A)
1	0.37	0.5	1.10	0.63
2	0.55	0.75	1.60	0.92
3	0.75	1	2.20	1.27
4	1.1	1.5	3.10	1.79
5	1.5	2	4.20	2.42
6	2.2	3	6.30	3.64
7	3.7	5	10.5	6.06
8	5.5	7.5	15.6	9.01
9	7.5	10	21.2	12.24
10	9.3	12.5	26.3	15.18
11	11	15	31.1	17.95
12	15	20	42.5	24.54
13	18.5	25	52.3	30.18
14	22	30	62.3	35.96
15	26	35	73.6	42.49
16	30	40	85.0	49.06
17	37	50	104.9	60.56
18	45	60	127.6	73.68
19	55	75	156.0	90.07
20	75	100	212.8	122.87
21	90	125	255.2	147.25
22	110	150	311.8	180.05
23	132	180	374.3	216.13
24	143	192	405.8	234.25

Calculation Procedure

Step-1: Select Motor

• Click the Motor Output (kW/HP) dropdown.

• Choose your motor rating from the list.

• Fields auto generate:

> Motor Power Output (kW)

> Full Load Current (Line) – A

> Full Load Current (Phase) – A

Step-2: Review Parameters

• Verify motor specifications that are correct.

• All fields are read only for accuracy.

• Parameters are come from the motor database.

Step-3: Calculate Cable Sizes

• Click the Calculate Cable Sizes – button.

• Page automatically scrolls to results section

• Results display for both DOL and Star Delta starters.

Step-4: Interpret Results

DOL Starter Results

Starter Current: Full line current (FLC) value

Backup Fuse: Calculated the fuse rating (1.5x multiplier)

Supply Cable (Al): Aluminum cable size in mm²

Supply Cable (Cu): Copper cable size in mm²

Overload Range: 50-90 A (typical)

Max Fuse: 125 A (DOL limit)

Star Delta Results

Motor Current: Reduced current (Line Current / √3)

Backup Fuse: Lower fuse rating due to the reduced current.

Supply Cable (Al): Same as DOL (same current)

Supply Cable (Cu): Same as DOL

Motor Cable (Al): Reduced size for the lower current.

Motor Cable (Cu): Reduced size for the lower current.

Overload Range: 38-63 A (typical).

Max Fuse: 100 A (Star Delta limit).

Step-5: Select Cable Type

Aluminum: Lighter, cheaper and standard for the long runs

Copper: In the short runs, it is more conductive and standard but it is also more expensive.

Cable Sizing Reference

Cable sizes are selected based on the full load current with a 1.5 x safety factor for fuse protection:

Formula

Fuse Rating = Full Load Current x 1.5 (rounded to nearest 10A)

Current to Cable Size Mapping

Aluminum Cables

S.No	Current (A)	Recommended Cable Size (mm²)
1	≤ 20	2.5
2	≤ 25	4
3	≤ 35	6
4	≤ 50	10
5	≤ 70	16
6	≤ 100	25
7	≤ 135	35
8	≤ 180	50
9	≤ 240	70
10	≤ 310	95
11	≤ 385	120
12	≤ 450	150

Copper Cables

S.No	Current (A)	Recommended Cable Size (mm²)
1	≤ 20	1.5
2	≤ 25	2.5
3	≤ 35	4
4	≤ 50	6
5	≤ 70	10
6	≤ 100	16
7	≤ 135	25
8	≤ 180	35
9	≤ 240	50
10	≤ 310	70
11	≤ 385	95
12	≤ 450	120

FAQ

1). What is the difference between Line current and Phase current?

Line current flows in the primary supply cable (3 conductors in 3-phase system). 

Phase current is the electric current in each of the individual phase. 

In a balanced 3-phase system they are related by: 

Line Current = Phase Current x √3 ≈ 1.732 x Phase Current.

2). Why are Star Delta cables smaller?

Star Delta reduces the starting current to approximately 1/3 of the DOL value. 

Since cables carry this reduced current smaller cable sizes are sufficient on the motor side. 

The supply side cables remain the same size as DOL to manage the full-time operating current.

3). What does Backup Fuse mean?

The backup fuse is used to protects the primary supply cable from overload and short circuits. 

It is sized at 1.5x the full load current rounding up to the nearest standard fuse size (10A increments).

Important Notes

• Ensure compliance with IS 1554, IEC 60245 (or) equivalent.

• Use armored cables in corrosive/mechanical hazard areas.

• Ensure proper earthing and grounding.

• Utilize surge protection devices for sensitive equipment.

• Consult your local electrical inspector.

• Reference IEC 60364 / IS 1554 standards.

• Contact motor manufacturer for specifications.

• Engage a qualified electrical engineer.