Breaker Load Calculator for Sub Panel
'/%3E%3Ccircle cx='48' cy='39' r='19' fill='%23f2c9a5'/%3E%3Cpath d='M27 35c3-16 39-17 42 2-8-8-27-9-42-2z' fill='%23374151'/%3E%3Cpath d='M21 86c5-24 49-28 56 0z' fill='%232563eb'/%3E%3Ccircle cx='41' cy='41' r='2' fill='%23111827'/%3E%3Ccircle cx='55' cy='41' r='2' fill='%23111827'/%3E%3Cpath d='M42 52c4 3 9 3 13 0' stroke='%2392400e' stroke-width='3' fill='none' stroke-linecap='round'/%3E%3C/svg%3E)
Reviewed by Calculator Editorial Team
Determine the correct breaker size for your sub panel with our breaker load calculator. This tool helps electricians and DIYers ensure proper electrical safety by calculating the appropriate circuit breaker size based on the total load of connected devices.
How to Use This Calculator
Using our breaker load calculator is simple. Follow these steps to get an accurate result:
- Enter the total load in amperes (A) for your sub panel
- Select the type of circuit (AC or DC)
- Choose the voltage level (120V, 240V, etc.)
- Click "Calculate" to get the recommended breaker size
- Review the result and any additional recommendations
The calculator will provide the appropriate breaker size based on standard electrical codes and safety margins.
Formula Explained
The breaker size is determined using the following formula:
Breaker Size (A) = Total Load (A) × Safety Factor
Where the safety factor is typically 1.25 for residential circuits and 1.4 for commercial circuits.
This formula accounts for the maximum current that can safely flow through the circuit while considering potential overloads and voltage drops.
For more precise calculations, additional factors such as wire gauge, conductor material, and ambient temperature may need to be considered.
Worked Example
Let's calculate the breaker size for a sub panel with a total load of 120A in a residential setting.
- Total Load = 120A
- Safety Factor = 1.25
- Breaker Size = 120 × 1.25 = 150A
Therefore, a 150A breaker would be appropriate for this sub panel.
Note: Always consult local electrical codes and a licensed electrician for final installation decisions.
Frequently Asked Questions
What is the difference between a main breaker and a sub panel breaker?
The main breaker protects the entire electrical system, while sub panel breakers protect specific circuits within the panel. Sub panel breakers are typically smaller and handle lower current loads.
Can I use a larger breaker than recommended?
No, using a larger breaker than recommended can create a fire hazard by allowing excessive current to flow. Always use the calculated breaker size or smaller.
What happens if I use the wrong breaker size?
Using a breaker that's too small can cause overheating and potential fire risk, while using one that's too large can lead to electrical shock hazards. Always use the proper breaker size for your load.