Circuit breakers are made in a series of standard rated currents, so a design never uses the exact design current: it takes the next standard rating that still protects the cable. This page lists the preferred MCB ratings of IEC 60898-1 with the instantaneous trip bands of the B, C and D curves, and the MCCB ratings commonly offered by manufacturers.
For each MCB rating the table also gives the conventional tripping current I2 = 1.45 × In, which IEC 60364-4-43 compares with 1.45 × Iz of the cable.
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MCB ratings and trip bands (IEC 60898-1)
Instantaneous (magnetic) trip band in amperes: the breaker trips without intentional delay somewhere inside the band, and is guaranteed to trip at its upper end.
Rated current In (A)
I2 = 1.45 In (A)
Type B: 3–5 × In (A)
Type C: 5–10 × In (A)
Type D: 10–20 × In (A)
6 A
8.7
18 – 30
30 – 60
60 – 120
8 A
11.6
24 – 40
40 – 80
80 – 160
10 A
14.5
30 – 50
50 – 100
100 – 200
13 A
18.85
39 – 65
65 – 130
130 – 260
16 A
23.2
48 – 80
80 – 160
160 – 320
20 A
29
60 – 100
100 – 200
200 – 400
25 A
36.25
75 – 125
125 – 250
250 – 500
32 A
46.4
96 – 160
160 – 320
320 – 640
40 A
58
120 – 200
200 – 400
400 – 800
50 A
72.5
150 – 250
250 – 500
500 – 1,000
63 A
91.35
189 – 315
315 – 630
630 – 1,260
80 A
116
240 – 400
400 – 800
800 – 1,600
100 A
145
300 – 500
500 – 1,000
1,000 – 2,000
125 A
181.3
375 – 625
625 – 1,250
1,250 – 2,500
Common MCCB rated currents
IEC 60947-2 does not fix a list of MCCB ratings. These values are widely offered across manufacturers' frame sizes, often with adjustable thermal and magnetic settings; check the range of the actual product.
16 A
20 A
25 A
32 A
40 A
50 A
63 A
80 A
100 A
125 A
160 A
200 A
250 A
320 A
400 A
500 A
630 A
800 A
1000 A
1250 A
1600 A
How the values are calculated
Ib ≤ In ≤ Iz
I2 ≤ 1.45 × Iz (MCB to IEC 60898-1: I2 = 1.45 × In)
Type B: 3 × In < Im ≤ 5 × In
Type C: 5 × In < Im ≤ 10 × In
Type D: 10 × In < Im ≤ 20 × In
Worked example
A circuit with design current Ib = 28 A on a cable rated Iz = 36 A. The smallest standard MCB not below 28 A is 32 A, and 28 ≤ 32 ≤ 36 holds.
I2 = 1.45 × 32 = 46.4 A
1.45 × Iz = 1.45 × 36 = 52.2 A
46.4 A ≤ 52.2 A ✓
Type C band: 160 – 320 A
With a type C device, the earth-fault or short-circuit current at the far end of the circuit must reach at least 320 A (the top of the band) for the breaker to be sure of tripping instantaneously.
Notes and limits
The MCB list is the series of preferred values in IEC 60898-1 up to 125 A; manufacturers also make some intermediate and smaller ratings.
Type B suits resistive loads and long circuits, type C general and motor circuits, type D high-inrush loads such as transformers; a D curve on a long cable may not reach its instantaneous band.
The rated current says nothing about breaking capacity. Icn (IEC 60898-1) or Icu and Ics (IEC 60947-2) must be at least the prospective short-circuit current where the device is installed.