Distribution box circuit breaker ratings

A distribution box, also known as a main lug panel (MLP) or a load center, is a type of electrical panel that distributes power from the main electrical service to various circuits in a building. Circuit breakers are an essential component of a distribution box, and they have specific ratings that determine their capacity to handle electrical current.

Here are some common circuit breaker ratings you may find in a distribution box:

  1. Ampere (A) Rating: This is the maximum amount of current a circuit breaker can handle without tripping. Common ampere ratings for residential circuit breakers are:
    • 15 A (for small appliances and lighting)
    • 20 A (for general-purpose circuits)
    • 30 A (for larger appliances and circuits)
    • 40 A (for heavy-duty circuits)
    • 50 A (for high-power circuits)
  2. Voltage (V) Rating: This is the maximum voltage a circuit breaker can handle. Common voltage ratings for residential circuit breakers are:
    • 120/240 V (for single-phase, 120/240-volt systems)
    • 208/240 V (for three-phase, 208/240-volt systems)
  3. Interrupting Rating (A): This is the maximum amount of current a circuit breaker can interrupt (or trip) without causing damage. This rating is usually higher than the ampere rating.
  4. Short-Circuit Current Rating (A): This is the maximum amount of current a circuit breaker can handle in the event of a short circuit. This rating is usually higher than the interrupting rating.
  5. Ground Fault Protection (GFP) Rating: This is the maximum amount of ground fault current a circuit breaker can detect and trip on. Common GFP ratings are:
    • 30 mA (for general-purpose circuits)
    • 60 mA (for heavy-duty circuits)
    • 100 mA (for high-power circuits)

When selecting circuit breakers for a distribution box, it's essential to ensure that they meet the following criteria:

  1. The ampere rating matches the load requirements of the circuit.
  2. The voltage rating matches the voltage of the electrical system.
  3. The interrupting rating is sufficient to handle the maximum short-circuit current.
  4. The short-circuit current rating is sufficient to handle the maximum short-circuit current.
  5. The ground fault protection rating is sufficient to detect and trip on ground faults.

It's always recommended to consult the manufacturer's specifications and local electrical codes to ensure that the circuit breakers you choose meet the necessary ratings and requirements.