When selecting an MCCB (Moulded Case Circuit Breaker), most people focus on current rating (In) or number of poles, but two of the most critical safety parameters are often misunderstood or ignored:
👉 Icu and Ics
These values decide whether an MCCB can safely interrupt fault current—and whether it can continue operating afterward.
In this blog, we’ll explain Icu and Ics in MCCB in the simplest possible way, using practical examples and real-world application logic.
Why Icu and Ics Matter in MCCB Selection
Short-circuit faults generate extremely high current (sometimes tens of thousands of amps).
If the MCCB is not rated correctly, it may:
-
Fail to interrupt the fault
-
Get permanently damaged
-
Become a fire hazard
-
Shut down the entire system
That’s why Icu and Ics are not optional specs—they are core safety parameters.
What is Icu in MCCB? (Ultimate Breaking Capacity)
Definition (Simple Language)
Icu is the maximum short-circuit current an MCCB can safely break once without exploding or causing danger.
👉 Think of Icu as the maximum emergency limit.
In technical terms:
-
Icu = Ultimate Short-Circuit Breaking Capacity
-
Measured in kA (kiloampere)
-
Tested as per IEC 60947-2
Example:
If an MCCB has:
-
Icu = 36 kA
It means:
-
The MCCB can interrupt a short-circuit current of 36,000 amperes
-
But may not remain usable afterward
⚠️ After breaking current at Icu level, the MCCB:
-
Might be damaged
-
Might need replacement
-
Is not guaranteed to function again
What is Ics in MCCB? (Service Breaking Capacity)
Definition (Simple Language)
Ics is the short-circuit current an MCCB can break and still remain operational afterward.
👉 Think of Ics as the safe, repeatable working limit.
In technical terms:
-
Ics = Service Short-Circuit Breaking Capacity
-
Expressed as a percentage of Icu
-
Typical values: 25%, 50%, 75%, or 100% of Icu
Example:
If an MCCB has:
-
Icu = 36 kA
-
Ics = 75%
Then:
-
Ics = 27 kA
Meaning:
-
The MCCB can interrupt 27,000 A
-
AND continue operating normally after the fault
Icu vs Ics: Key Differences (Easy Table)
| Parameter | Icu | Ics |
|---|---|---|
| Full form | Ultimate Breaking Capacity | Service Breaking Capacity |
| Purpose | Maximum fault it can break once | Fault it can break and still work |
| Reusability after fault | Not guaranteed | Guaranteed |
| Safety relevance | Emergency survival | Real-world reliability |
| Ideal selection focus | ❌ No | ✅ Yes |
👉 Always prioritize Ics, not just Icu.
Why Ics is More Important Than Icu in Real Applications
Many buyers make this mistake:
“This MCCB has 50kA Icu, so it’s very strong.”
But if:
-
Ics is only 25% of Icu
-
Actual fault current is close to system fault level
Then:
-
MCCB may trip
-
But will need replacement
-
Causing downtime and safety risk
Rule of thumb:
✅ Your system fault current should always be ≤ Ics, not Icu.
Practical Example (Real-Life Scenario)
Industrial Panel Example:
-
Calculated fault current at incomer: 30 kA
Wrong MCCB Selection:
-
MCCB with Icu = 36 kA
-
Ics = 18 kA (50%)
❌ Result:
-
MCCB may interrupt fault
-
But will be permanently damaged
-
Panel downtime + replacement cost
Correct MCCB Selection:
-
MCCB with Icu = 36 kA
-
Ics = 27–36 kA (75%–100%)
âś… Result:
-
Safe fault interruption
-
MCCB remains functional
-
Higher system reliability
Common Ics Percentages You’ll See in MCCBs
| Ics % of Icu | Typical Use |
|---|---|
| 25% | Low-risk, non-critical circuits |
| 50% | Light commercial applications |
| 75% | Industrial & commercial panels |
| 100% | Critical infrastructure, data centers |
👉 For industrial and commercial projects, 75% or 100% Ics is strongly recommended.
How to Check Icu and Ics on an MCCB?
You can find Icu and Ics:
-
On the MCCB label
-
In the technical datasheet
-
Marked as:
-
Icu = 36kA -
Ics = 75% Icu
-
⚠️ Never rely only on verbal confirmation—always verify datasheets.
Why BCH Electric MCCBs Are Trusted for High Ics & Icu Performance
When selecting MCCBs, brand reliability matters as much as ratings.
BCH Electric is widely regarded as a leading MCCB brand in India, especially for applications where short-circuit safety and long-term reliability are critical.
What makes BCH Electric MCCBs stand out:
-
High Ics values suitable for real industrial fault conditions
-
Compliance with IEC 60947-2 standards
-
Robust breaking mechanism for repeated fault handling
-
Consistent performance under Indian grid conditions
-
Trusted by panel builders, EPCs, and consultants
For projects where downtime and safety cannot be compromised, BCH Electric MCCBs are often the preferred choice.
Common Mistakes to Avoid While Selecting MCCB
-
Selecting based only on current rating (In)
-
Looking at Icu but ignoring Ics
-
Choosing lower Ics to reduce cost
-
Not matching MCCB ratings with actual fault level
-
Using unknown or non-certified brands
Final Selection Guideline (Simple & Safe)
âś” Calculate system fault current
✔ Choose MCCB with Ics ≥ system fault current
âś” Prefer 75% or 100% Ics for industrial use
âś” Verify IEC compliance
âś” Use a trusted MCCB brand like BCH Electric
Conclusion
-
Icu tells you how much fault current an MCCB can survive once
-
Ics tells you how much fault current it can handle safely and repeatedly
-
For real-world safety, Ics is more important than Icu
-
Choosing a reliable brand like BCH Electric ensures consistent protection, compliance, and peace of mind
