# Electrical Cable Sizing

**URL:** <https://forumautomation.com/t/electrical-cable-sizing/14434>\
**Category:** Electrical\
**Tags:** cable-selction\
**Created:** [September 21, 2026, 9:38am UTC](https://forumautomation.com/t/electrical-cable-sizing/14434 "2026-09-21T09:38:15Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Rabert](https://forumautomation.com/user_avatar/forumautomation.com/rabert/32/6784_2.png) [@Rabert](https://forumautomation.com/u/Rabert)\
**Post date:** [September 21, 2026, 9:38am UTC](https://forumautomation.com/t/electrical-cable-sizing/14434/1 "2026-09-21T09:38:16Z")

</div>

## Electrical Cable Sizing

Selecting the correct electrical cable size ensures safe operation, minimizes voltage drop, prevents overheating, and provides adequate short-circuit protection for the entire installation.

 ![2](https://cdn.forumautomation.com/original/2X/f/f05ba6065b76527fea4fca94013fe488a21e7326.jpeg)

### Where:

- P = Power (Watts)

- V = Voltage (Volts)

- I = Current (Amps)

- PF = Power Factor

- η = Efficiency

### Step 1: Calculate Load Current

For a 3-phase circuit:

![image](https://cdn.forumautomation.com/original/2X/f/fa0bbf327d982669231b578d39c8f12ced34f64d.png)

For a single-phase circuit:

![image](https://cdn.forumautomation.com/original/2X/5/513f92cd9c228cf01a0e282d81c7ed6ef11aed29.png)

### Step 2: Select the Cable Size

Choose a cable with an ampacity greater than the calculated load current after applying all installation correction factors.

Consider:

- Ambient temperature

- Installation method (tray, conduit, buried, etc.)

- Number of grouped cables

- Cable insulation type

- Voltage drop

- Short-circuit withstand capacity

### Step 3: Perform a Voltage Drop Check

For a 3-phase circuit:

![image](https://cdn.forumautomation.com/original/2X/7/7120d69ba86ca0ac28c9b061547aa59b243e0be2.png)

Where:

- L = Cable length

- R = Resistance

- X = Reactance

- ϕ\phiϕ = Power factor angle

The final cable selection must satisfy both the required ampacity and the permissible voltage drop under the actual installation conditions.

## Calculator

### [LT & HT Cable Sizing Calculator](https://forumelectrical.com/lt-ht-cable-sizing-calculator/)