MCCB vs MCB: Which Does Your Panel Board Need?

Use an MCB (miniature circuit breaker) for final circuits up to 125 A where the prospective fault current at the board is within its breaking capacity, typically 6 kA or 10 kA. Use an MCCB (moulded case circuit breaker) for feeders and sub-mains, wherever the fault level is higher, and wherever you need adjustable or time-delayed protection to keep upstream breakers selective. In practice the choice comes down to three numbers at each board: the design current, the prospective fault current, and the selectivity you need with the device upstream.

Below: what each standard tests, how to estimate fault level from the transformer, selectivity between an MCCB and the MCBs below it, derating in Singapore switch rooms, and a board-by-board selection matrix, using Himel and Schneider Electric technical data.

In this article

• What is the difference between an MCCB and an MCB?
• IEC 60898-1 vs IEC 60947-2: why the standard matters
• Breaking capacity: start from the fault level at the board
• Selectivity: will the right breaker trip?
• When should I use an MCCB instead of an MCB?
• MCCB vs MCB selection matrix
• Temperature, derating and the Singapore switch room
• Common mistakes and what we check on site
• Breakers we supply and how to get a schedule checked
• Frequently asked questions about MCCB vs MCB
• Sources

What is the difference between an MCCB and an MCB?

Both open automatically on overload and short circuit. They differ in the standard they are tested to and in the size and adjustability of the trip unit. IEC 60898-1 covers AC circuit-breakers for household and similar installations with a rated voltage up to 440 V between phases, a rated current up to 125 A and a rated short-circuit capacity up to 25,000 A. IEC 60947-2:2024 covers circuit-breakers with main contacts rated up to 1,000 V AC or 1,500 V DC, intended to be installed and operated by instructed or skilled persons.

For product detail, see how to choose the right Himel HDB9H MCB and the Himel HDM3 MCCB explained.

IEC 60898-1 vs IEC 60947-2: why the standard matters

The standards describe short-circuit ratings differently, so two datasheets are not always directly comparable.

• Icn (IEC 60898-1) is the MCB’s rated short-circuit capacity, a single value such as the 10 kA on the Himel HDB9H63A2B20 datasheet (energy limitation class 3, B-curve trip at 3–5 × In).
• Icu (IEC 60947-2) is the rated ultimate short-circuit breaking capacity. Ics is the rated service short-circuit breaking capacity, expressed as a percentage of Icu. Schneider Electric’s FAQ on Icu and Ics notes that for MCBs Ics is usually 50–100% of Icu.
• Utilisation category exists only under IEC 60947-2. Category B breakers have a short-time withstand rating (Icw), so they can be delayed to let a downstream breaker clear the fault. In the Himel HDM3/3L/3E catalogue, the HDM3E electronic MCCBs from the 400 A frame upwards are listed as category B, with an Icw rating for each frame.

Some DIN-rail breakers sit in between. The Himel HDB3w-125 100 A datasheet lists IEC 60947-2 as its standard, a 10 kA breaking capacity and a magnetic tripping limit of 8.5 × In. Check the standard on the datasheet, not the shape of the device.

Schneider Electric’s guide to B, C and D curves gives about 3–5 × In for B, 5–10 × In for C and 10–14 × In for its D curve. That instantaneous threshold matters again for selectivity.

Breaking capacity: start from the fault level at the board

BS 7671, on which Singapore’s SS 638 is based, requires each protective device’s breaking capacity to be at least the maximum prospective fault current where it is installed. The exception is tested back-up protection from an upstream device (cascading).

Schneider Electric’s Cahier Technique 158 on short-circuit calculation gives a first estimate: neglecting upstream impedance, the fault current at the transformer’s LV terminals is about its rated current divided by its short-circuit voltage (usc), which it lists as 4% for 630 kVA up to 7% for 2,000 kVA. At 400 V:

So breakers at the main switchboard of a building on a 1,000 kVA transformer need roughly 30 kA or more: MCCB or air circuit-breaker territory. Cable impedance lowers the fault level further out, so a board at the end of a long sub-main may be within a 10 kA MCB’s rating. Only a calculation for that board tells you.

Icu is not the whole story

Icu says the MCCB can interrupt the fault; Ics says whether it is still fit for service afterwards. The Himel HDM3S adjustable thermal-magnetic range is published with Ics = 100% of Icu: 35/35 kA for the 160 A frame and 50/50 kA for the 250, 400 and 630 A frames. Where continuity matters, compare Ics with the fault level too.

Selectivity: will the right breaker trip?

Selectivity (discrimination) means only the breaker nearest the fault opens. Schneider Electric’s Cahier Technique 167 defines discrimination as total if only the most downstream breaker trips for all fault current values, and partial if that holds only up to a certain fault level. It sets out practical rules:

• Overload zone: selectivity is generally achieved if the ratio of the upstream to the downstream long-time (thermal) thresholds is greater than 1.6.
• Current discrimination: the upstream instantaneous threshold should be at least 1.5 times the downstream one; this generally gives only partial discrimination.
• Time discrimination gives total selectivity by delaying the upstream breaker, which needs an intentional time delay and short-time withstand (category B).

Worked example: 63 A MCBs under a 250 A MCCB

A board is fed by a Himel HDM3-250 thermal-magnetic MCCB, whose fixed magnetic trip is 10 × In = 2,500 A (HDM3 catalogue). Its outgoing 63 A C-curve MCBs trip instantaneously between 315 A and 630 A.

• Overload: 250 ÷ 63 ≈ 4, above 1.6.
• Short circuit: 2,500 ÷ 630 ≈ 4, above 1.5. The catalogue’s magnetic test requires no trip at 80% of Ii, so the MCCB should hold for faults up to about 2,000 A.
• Above about 2,000 A, both may trip; only the manufacturer’s coordination tables can confirm which clears first.

So the pair is selective for faults out on the final circuits and only partially selective close to the board. For total selectivity, use an upstream breaker with a short-time delay, such as the HDM3E with adjustable Isd and tsd. The catalogue notes that “short time delay protection is used to ensure the selectivity coordination with the downstream circuit breakers”.

When should I use an MCCB instead of an MCB?

Step up from an MCB to an MCCB when any one of these applies:

1. The design current exceeds the MCB range (125 A under IEC 60898-1; 63 A for the HDB9).
2. The calculated fault level exceeds the MCB’s Icn, and no tested cascading combination with the upstream device covers the difference.
3. You need time-delayed or adjustable protection for selectivity, typically on a sub-main board incomer.
4. The circuit feeds a motor. The HDM3 magnetic-only version trips at 12 × In and leaves overload protection to a separate relay; see our guides to the Himel HDR3S thermal overload relay and contactor selection. For small motors, a Himel HDP6 motor circuit breaker combines isolation, adjustable overload and short-circuit protection in one device.
5. The circuit serves a fire pump or essential services. SCDF’s Fire Code 2023, clause 5.2.3 calls for HRC fuses or MCCBs with magnetic release and does not permit thermal overload trips.
6. You need remote tripping or signalling, such as a shunt trip from the fire alarm panel, an undervoltage release, auxiliary contacts or a motor operator.

MCCB vs MCB selection matrix

For a typical commercial building (bands are examples; your design calculation decides):

Temperature, derating and the Singapore switch room

Thermal trip units are calibrated at a reference temperature. Singapore’s daytime maximum is typically 31–33 °C, according to the Meteorological Service Singapore, and an enclosed panel adds its own heat, so derating matters. The HDM3 catalogue gives these factors for 40 °C-calibrated products at 50 °C ambient: 0.89 for the HDM3-100, 0.85 for the HDM3-160/250, 0.87 for the HDM3-400/630 and 0.88 for the HDM3-800.

A 250 A HDM3-250 calibrated at 40 °C therefore carries about 250 × 0.85 ≈ 212 A in a 50 °C panel. Select the next rating or a 50 °C-calibrated reference (a “T” suffix in the HDM3S selection code). Most HDM3E frames need no derating up to 50 °C.

Common mistakes and what we check on site

• Comparing an MCB’s Icn with an MCCB’s Ics or Icu as if they were the same test. Compare like with like, at the same voltage.
• Using 6 kA MCBs in a board close to the transformer without a calculated fault level or a tested cascading combination.
• Assuming an MCB under an MCCB is always selective. It usually holds only up to the MCCB’s instantaneous threshold.
• Ignoring derating in hot switch rooms and enclosed panels.
• Leaving a thermal trip on a fire pump circuit, contrary to Fire Code clause 5.2.3.
• Approving a datasheet for one reference and ordering another, for example a 40 °C product when the schedule assumed 50 °C.

Our published case studies are drive and soft starter projects, so there is no breaker case study to cite here; these checks come from the data and standards above.

Breakers we supply and how to get a schedule checked

Trans-Digi Global is an authorised Himel distributor in Singapore. We stock the Himel HDB9 and HDB3w MCB ranges, the Himel HDM2 and HDM3 MCCB ranges, the HDP6 motor circuit breaker and the HDB3VR RCCB. Browse all moulded case circuit breakers and miniature circuit breakers.

Send your board schedule, the calculated fault level at each board and the upstream device through our contact page. We will confirm references and datasheets for your submission.

Frequently asked questions about MCCB vs MCB

What is the difference between an MCCB and an MCB?

An MCB is a DIN-rail breaker for final circuits, tested to IEC 60898-1 up to 125 A and 25 kA. An MCCB is tested to IEC 60947-2, covers ratings up to 1,600 A in the Himel HDM range, has higher breaking capacities and can have adjustable or time-delayed trip units.

When should I use a moulded case circuit breaker instead of an MCB?

Use an MCCB when the current is above the MCB range, when the fault level at the board is above the MCB’s breaking capacity, when you need adjustable or time-delayed protection for selectivity, or for motor and fire pump circuits.

Is a moulded case circuit breaker better than a miniature circuit breaker?

Neither is better in general. Each suits a different job. An MCB is the compact, economical choice for final circuits within its limits. An MCCB is needed where current, fault level or selectivity go beyond them.

Can an MCB be used above 63 A?

Yes, up to 125 A. IEC 60898-1 covers MCBs up to 125 A, and the Himel HDB3w-125 provides ratings up to 125 A in a 27 mm-per-pole DIN-rail format, certified to IEC 60947-2.

What breaking capacity does my breaker need?

At least the maximum prospective fault current where it is installed, unless a tested upstream device provides back-up protection. Near a 1,000 kVA transformer, a first estimate is about 29 kA. At remote boards it can be much lower, so calculate it board by board.

Will an MCB trip before the MCCB upstream of it?

For most faults on the final circuit, yes, if the MCCB’s instantaneous threshold is at least 1.5 times the MCB’s. For high faults close to the board, selectivity may be only partial. Check the manufacturer’s coordination tables, or use an upstream MCCB with a short-time delay.

Which standard governs breaker selection in Singapore?

Electrical installations are designed to SS 638, the Code of Practice for Electrical Installations, by a licensed electrical worker. The breakers themselves are tested to IEC 60898-1 (MCBs) or IEC 60947-2 (MCCBs).

Sources

• IEC, IEC 60898-1:2015 Circuit-breakers for overcurrent protection for household and similar installations, Part 1.
• IEC, IEC 60947-2:2024 Low-voltage switchgear and controlgear, Part 2: Circuit-breakers.
• Enterprise Singapore, SS 638:2018+C1:2020+A1:2022 Code of practice for electrical installations.
• Energy Market Authority, Circular RD/E01/2019: SS 638 Code of Practice for Electrical Installations.
• Schneider Electric, FAQ: utilisation category and Ics/Icu percentage.
• Schneider Electric, FAQ: what do B, C and D curves mean?.
• Schneider Electric, Cahier Technique 158: Calculation of short-circuit currents.
• Schneider Electric, Cahier Technique 167: Energy-based discrimination for low-voltage protective devices.
• Himel, HDM3/3L/3E Series MCCB catalogue (technical parameters, trip characteristics, temperature derating, HDM3S and HDM3E data).
• Himel, Panel Builder brochure (MCB and MCCB ranges).
• Himel, HDB9H63A2B20 product data sheet and HDB3W125H3C100 product data sheet.
• Singapore Civil Defence Force, Fire Code 2023, clause 5.2.
• Meteorological Service Singapore, Climate of Singapore.