How to Read the Nameplate of a MCCB
The nameplate of an MCCB (Molded Case Circuit Breaker) provides
crucial technical specifications needed for selecting, installing, and
operating the breaker safely in an electrical system. Let's break down each
parameter in detail.
1. Rated Insulation Voltage (Ui)
- Value: 750V
- Definition: This is the
maximum voltage level that the insulation of the breaker can withstand
without breaking down.
- Importance:
- Ensures the
breaker’s insulation can handle high operating voltages.
- Prevents
insulation failure due to overvoltage conditions.
2. Rated Impulse Withstand Voltage
(Uimp)
- Value: 8kV
- Definition: This indicates
the breaker’s ability to withstand high transient overvoltages, such as
those caused by lightning strikes or switching surges.
- Importance:
- Ensures the
MCCB can handle sudden voltage spikes without damage.
- Important for
surge protection and system reliability.
3. Rated Voltage (Ue)
- Values:
- 220/240V
- 380/415V
- 440V
- 500V
- 525V
- 660/690V
- Definition: The nominal
system voltage at which the MCCB is designed to operate.
- Importance:
- Ensures the
MCCB is suitable for the electrical system voltage.
- Using an MCCB
with an incorrect Ue may lead to improper operation or failure.
4. Ultimate Breaking Capacity (Icu)
- Values (based
on Ue):
- 220/240V → 85kA
- 380/415V → 36kA
- 440V → 35kA
- 500V → 25kA
- 525V → 25kA
- 660/690V → 25kA
- Definition: This is the
maximum fault current the MCCB can interrupt safely without being damaged.
- Importance:
- Helps in
selecting a breaker that can handle potential fault currents in the
system.
- Protects
electrical equipment from catastrophic failures due to short circuits.
5. Service Breaking Capacity (Ics)
- Values (based
on Ue):
- 220/240V → 85kA
- 380/415V → 36kA
- 440V → 35kA
- 500V → 25kA
- 525V → 25kA
- 660/690V → 25kA
- Definition: The maximum
fault current the MCCB can interrupt multiple times and still
remain operational.
- Importance:
- Indicates the
reliability and durability of the breaker under fault conditions.
- Higher Ics
means the MCCB can be reset and used again after a fault, rather than
requiring replacement.
6. Frequency
- Value: 50/60 Hz
- Definition: The MCCB is
designed to operate at either 50 Hz or 60 Hz electrical systems.
- Importance:
- Ensures
compatibility with the power system frequency (e.g., 50Hz in Europe and
60Hz in North America).
- Improper
frequency matching can lead to incorrect operation.
7. Category (Cat A)
- Definition: MCCBs are
categorized as Category A or Category B based on their performance.
- Cat A (No
Discrimination):
- Does not
require coordination (discrimination) with another breaker upstream.
- Used in
standalone applications where selectivity is not required.
- Cat B (With
Discrimination):
- Used in
applications where selective tripping is needed (e.g., coordinated
protection with upstream circuit breakers).
8. Standards Compliance
- Standard: IEC / EN
60947-2
- Definition: This
international standard specifies the performance, testing, and safety
requirements for circuit breakers.
- Importance:
- Ensures the
MCCB meets global electrical safety and performance regulations.
- Helps in
selecting an MCCB that complies with industry standards.
9. NEMA AB1 Ratings (HIC - High
Interrupting Capacity)
- Values:
- 240V → 85kA
- 480V → 35kA
- 600V → 8kA
- Definition: The NEMA
(National Electrical Manufacturers Association) rating is an
alternative standard used in North America.
- Importance:
- Helps in
selecting MCCBs based on NEMA standards, which are widely used in
industrial applications in the U.S. and Canada.
- The High
Interrupting Capacity (HIC) rating indicates the breaker’s ability to
handle high fault currents.
Final Interpretation
✔ Handles transient overvoltages up to 8kV