General & Planning · CEC Section 14 (Interrupting Capacity)

Fault Current Calculator

Estimate available short-circuit fault current (AIC) at your main panel to verify breaker interrupting ratings (typically 10,000 AIR / 10kAIC).

1. Utility & Service Inputs

Utility Transformer Rating (kVA)

Transformer Impedance (%Z)

Service Conductor Length (ft from transformer)

Service Wire Size (Aluminum or Copper)

2. Fault Capacity Results

CEC Rule 14-012

ESTIMATED SHORT CIRCUIT CURRENT

4,850 Amps

REQUIRED BREAKER INTERRUPTING RATING

10 kAIC (Standard)

Standard 10kA Breakers OK: Fault current is safely below standard 10,000 Amp (10kAIC) residential breaker limits.

Why Interrupting Rating Matters

If a dead short circuit occurs, the current spikes instantly to thousands of amperes until the main breaker trips.
Breakers must be rated to clear this fault current without exploding or welding their contacts closed (10,000 AIR / 10kAIC is standard for homes).
Shorter service drops closer to utility transformers yield higher potential fault currents.

Breaker interrupting ratings (AIC)

A breaker must safely interrupt the maximum fault current available at its location.

AIC rating	Where it applies
10 kA	Standard residential breakers — adequate for most homes
22 kA	Required where available fault current exceeds 10 kA (large services, close to utility transformer)
25 kA+	Commercial / multi-unit service equipment

If your panel is very close to a pad-mount transformer, ask your utility for the available fault current before replacing breakers.

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