23

Loadlimiter M

CB

s - Technical Information

22

Load

limit

er M

CB

s -

Tech

nica

l In

form

atio

n

LOADLIMITER MCBs

Where high prospective fault levels exist at the MCB distributionpoint then discrimination at short-circuit levels should beconsidered. This will require comparison of the device l2tcharacteristics for the prospective fault level concerned.Discrimination will be obtained at all fault levels for which theMCB total operating l2t is lower than the pre-arcing l2t of the devicenearer the supply.The information for typical cartridge fuses can be extracted fromcurves and is presented in tabular form below.

MAXIMUM BACK UP FUSE RATING FOR PROTECTIONRated

‘B’ Type ‘C’ Type ‘D’ TypeCurrent

In Fuse Link Rating (A)

6 63A 40A 40A10 80A 63A 63A16 80A 80A 80A20 80A 80A 80A25 100A 100A 100A32 100A 100A 100A40 125A 125A 125A50 160A 160A 160A63 160A 160A 160A

The fuse values given in this table cover worse case conditions.

MINIMUM FUSE RATING FOR DISCRIMINATIONRated

‘B’ Type ‘C’ Type ‘D’ TypeCurrent

In Fuse Link Rating (A)

6 20A 32A 25A10 20A 32A 40A16 32A 50A 63A20 40A 63A 63A25 50A 80A 80A32 63A 100A 100A40 80A 100A 125A50 100A 125A 125A63 125A 125A 125A

0,8

0,9

1,0

1,1

1,2

1,3

1,4

1,5

Ambient temperature °C

-25 -10 0 10 20 30 40 55

1340

32A63A8A

10A

Cor

rect

ion

fact

or K

υ

4x102

Prospective short circuit current ip/A

Let

- th

roug

h i2

t (A

mp2 s

ec)

103

6 8 103 2 3 4 6 104

HW

= 0

,01

sec.

8

In =

2

3

4

6

8104

2

3

4

6

8105

40 A50, 63 A

32 A25 A20 A16 A10 A

6 A

50 A

40 A

35 A

32 A

63 A80 A100 A

125 A

BS88 FUSE 160 A

2

1

Proo

f fac

tor

(K)

= I s

urge

/ Iho

ld

Pulse duration

90100

807060

50

40

30

20

109876

5

4

3

2

1

0.01 ms 0.1 ms 1 ms 10 ms

exampleAS16B

k = 4.2600 µs

‘B’, ‘C’ and ‘D’ Characteristic MCBs

Let

- th

roug

h i2

t (A

mp2 s

ec)

4x102

Prospective short circuit current ip/A

103

6 8 103 2 3 4 6

50 A

40 A

35 A

32 A

63 A80 A100 A

125 A

BS88 FUSE 160 A

In =

2

3

4

6

8104

2

3

4

6

8105

1

2

1 /2 C

YCLE

= 0

,01

sec.

6 A

10 A, 13 A16, 20 A

25 A, 32 A40, 50 A63 A

min melting I2t (pre-arching), e.g. In = 125A BS 88

max let-through I2t of MCB, e.g. 6A

1

2

PULSE TRIPPING OF LOADLIMITER MCBs

LOADLIMITER MCBs I2t LET THROUGH

The pulse tripping curve is used to calculate whether a circuit breakerwill remain ‘ON’ during a high surge current of short duration.

Example: for AS16B - 16A ‘B’ characteristic.

What size of current surge will the MCB withstand without tripping ifthe pulse length is 600µs.

I surge = K x I hold

I hold = 3 x In for ‘B’ characteristic5 x In for ‘C’ characteristic

10 x In for ‘D’ characteristic

I surge = 4.2 x 3 x 16 = 172.8 Amps

AS16B MCB will withstand a current surge of 172.8A for 600µswithout tripping.

Effect of ambient temperature on the current carrying capacity ofMCB’s.

Example: for 10A MCB at 40°C.

1. For continuous loads ≤ 1 hour

I = In x Ku = 10 x 1.05 = 10.5 Amps

Note: MCB’s are calibrated at 30°C to carry1.13 x In for 1 hour without tripping.

2. For continuous loads > 1 hour

I = 0.9 x In x Ku = 0.9 x 10 x 1.05 = 9.45 Amps

Note: For continuous loads greater than 1 hour the MCB must bederated by 0.9 to cater for thermal influence over a long period.

‘D’ Characteristic

AMBIENT TEMPERATURE CORRECTION

‘B’ & ‘C’ Characteristic

‘B’ CharacteristicMCBs FUSE SIZES

InA 20 25 35 50 63 80 100 125 160

6 0.5 0.8 1.7 3.1 7 10 10 10 10

10 0.4 0.7 1.4 2.3 3.4 4.8 7.5 10 10

13 0.7 1.4 2.3 3.4 4.8 7.5 10 10

16 1.3 2.0 2.9 4.2 6 9.5 10

20 1.9 2.7 3.8 5.6 8.5 10

25 1.8 2.6 3.6 5.4 8 10

32 2.4 3.2 4.2 6.8 10

40 3.2 4.2 6.8 9.5

50/63 no selectivity 3.8 5.7 8.5

‘C’ CharacteristicMCBs Fuse sizes

InA 20 25 35 50 63 80 100 125 160

6 0.5 0.8 1.7 3.1 7 10 10 10 10

10 1.4 2.3 3.4 4.8 7.5 10 10

13 2.3 3.4 4.8 7.5 10 10

16 2.0 2.9 4.2 6 9.5 10

20 2.7 3.8 5.6 8.5 10

25 3.6 5.4 8 10

32 4.2 6.8 10

40 4.2 6.8 9.5

50/63 no selectivity 5.7 8.5

‘D’ CharacteristicMCBs Fuse sizes

InA 20 25 35 50 63 80 100 125 160

6 0.7 1.7 3 5.9 6 6 6 6

10 1.3 2.2 3.6 6 6 6 6

13 1.7 2.5 4 6 6 6

16 1.6 2.2 3.1 4.6 6 6

20 2.2 3.1 4.6 6 6

25 3.1 4.6 8 6

32 2.6 3.5 6 6

40 3.5 6 6

40/50 5.5 6

63 no selectivity

MAXIMUM EARTH FAULT LOOP IMPEDANCESZs (Ohms) for µo=230V~➀

Rating B Characteristic C Characteristic D Characteristic(A) to<0.4s to<5s to<0.4s to<5s to<0.4s to<5s

6 7.6 7.6 3.8 5.9 2.7 3.6

8 2.8 5.7 2 2.7

10 4.6 4.6 2.3 3.5 1.6 2.9

16 2.9 2.9 1.4 2.2 1 1.8

20 2.3 2.3 1.1 1.7 0.8 1.4

25 1.8 1.8 0.9 1.4 0.6 1.1

32 1.4 1.4 0.7 1.1 0.5 0.9

40 1.1 1.1 0.6 0.9 0.4 07

50 0.9 0.9 0.5 0.7 0.3 0.6

63 0.7 0.7 0.4 0.6 0.25 0.46

➀ µo = rated voltage to earthed conductors for µ0=240v~ Zs•1.04 applies.

DISCRIMINATION

The Wiring Regulations require (533-6) that ‘the characteristics andsettings of devices for overcurrent protection shall be such that properdiscrimination in their operation is assured’. At overload levels acomparison of the devices’ time/current characteristics will showwhether discimination is acheived. For example, the relationshipbetween MCBs as final circuit devices, and cartridge fuses may besummarised.

SHORT CIRCUIT DISCRIMINATION LEVELS

PROSPECTIVE FAULT CURRENT

Given proper design of an installation the 10kA rating ofLoadlimiter MCBs means that they will deal with prospective faultcurrents up to 10,000 amps without the need for additional backup protection. In addition, faults rarely occur at the board itself and are mostlikely at points remote from the board where prospective current

is reduced considerably by the fault loop impedance. In a typical breaking operation when the prospective fault current is10,000 amps, the combination of forced contact separation and rapidarc extinction produces a limiting effect on the fault current so that itnever reaches the prospective peak value.

23

Loadlimiter M

CB

s - Technical Information

22

Load

limit

er M

CB

s -

Tech

nica

l In

form

atio

n

LOADLIMITER MCBs

Where high prospective fault levels exist at the MCB distributionpoint then discrimination at short-circuit levels should beconsidered. This will require comparison of the device l2tcharacteristics for the prospective fault level concerned.Discrimination will be obtained at all fault levels for which theMCB total operating l2t is lower than the pre-arcing l2t of the devicenearer the supply.The information for typical cartridge fuses can be extracted fromcurves and is presented in tabular form below.

MAXIMUM BACK UP FUSE RATING FOR PROTECTIONRated

‘B’ Type ‘C’ Type ‘D’ TypeCurrent

In Fuse Link Rating (A)

6 63A 40A 40A10 80A 63A 63A16 80A 80A 80A20 80A 80A 80A25 100A 100A 100A32 100A 100A 100A40 125A 125A 125A50 160A 160A 160A63 160A 160A 160A

The fuse values given in this table cover worse case conditions.

MINIMUM FUSE RATING FOR DISCRIMINATIONRated

‘B’ Type ‘C’ Type ‘D’ TypeCurrent

In Fuse Link Rating (A)

6 20A 32A 25A10 20A 32A 40A16 32A 50A 63A20 40A 63A 63A25 50A 80A 80A32 63A 100A 100A40 80A 100A 125A50 100A 125A 125A63 125A 125A 125A

0,8

0,9

1,0

1,1

1,2

1,3

1,4

1,5

Ambient temperature °C

-25 -10 0 10 20 30 40 55

1340

32A63A8A

10A

Cor

rect

ion

fact

or K

υ

4x102

Prospective short circuit current ip/A

Let

- th

roug

h i2

t (A

mp2 s

ec)

103

6 8 103 2 3 4 6 104

HW

= 0

,01

sec.

8

In =

2

3

4

6

8104

2

3

4

6

8105

40 A50, 63 A

32 A25 A20 A16 A10 A

6 A

50 A

40 A

35 A

32 A

63 A80 A100 A

125 A

BS88 FUSE 160 A

2

1

Proo

f fac

tor

(K)

= I s

urge

/ Iho

ld

Pulse duration

90100

807060

50

40

30

20

109876

5

4

3

2

1

0.01 ms 0.1 ms 1 ms 10 ms

exampleAS16B

k = 4.2600 µs

‘B’, ‘C’ and ‘D’ Characteristic MCBs

Let

- th

roug

h i2

t (A

mp2 s

ec)

4x102

Prospective short circuit current ip/A

103

6 8 103 2 3 4 6

50 A

40 A

35 A

32 A

63 A80 A100 A

125 A

BS88 FUSE 160 A

In =

2

3

4

6

8104

2

3

4

6

8105

1

2

1 /2 C

YCLE

= 0

,01

sec.

6 A

10 A, 13 A16, 20 A

25 A, 32 A40, 50 A63 A

min melting I2t (pre-arching), e.g. In = 125A BS 88

max let-through I2t of MCB, e.g. 6A

1

2

PULSE TRIPPING OF LOADLIMITER MCBs

LOADLIMITER MCBs I2t LET THROUGH

The pulse tripping curve is used to calculate whether a circuit breakerwill remain ‘ON’ during a high surge current of short duration.

Example: for AS16B - 16A ‘B’ characteristic.

What size of current surge will the MCB withstand without tripping ifthe pulse length is 600µs.

I surge = K x I hold

I hold = 3 x In for ‘B’ characteristic5 x In for ‘C’ characteristic

10 x In for ‘D’ characteristic

I surge = 4.2 x 3 x 16 = 172.8 Amps

AS16B MCB will withstand a current surge of 172.8A for 600µswithout tripping.

Effect of ambient temperature on the current carrying capacity ofMCB’s.

Example: for 10A MCB at 40°C.

1. For continuous loads ≤ 1 hour

I = In x Ku = 10 x 1.05 = 10.5 Amps

Note: MCB’s are calibrated at 30°C to carry1.13 x In for 1 hour without tripping.

2. For continuous loads > 1 hour

I = 0.9 x In x Ku = 0.9 x 10 x 1.05 = 9.45 Amps

Note: For continuous loads greater than 1 hour the MCB must bederated by 0.9 to cater for thermal influence over a long period.

‘D’ Characteristic

AMBIENT TEMPERATURE CORRECTION

‘B’ & ‘C’ Characteristic

‘B’ CharacteristicMCBs FUSE SIZES

InA 20 25 35 50 63 80 100 125 160

6 0.5 0.8 1.7 3.1 7 10 10 10 10

10 0.4 0.7 1.4 2.3 3.4 4.8 7.5 10 10

13 0.7 1.4 2.3 3.4 4.8 7.5 10 10

16 1.3 2.0 2.9 4.2 6 9.5 10

20 1.9 2.7 3.8 5.6 8.5 10

25 1.8 2.6 3.6 5.4 8 10

32 2.4 3.2 4.2 6.8 10

40 3.2 4.2 6.8 9.5

50/63 no selectivity 3.8 5.7 8.5

‘C’ CharacteristicMCBs Fuse sizes

InA 20 25 35 50 63 80 100 125 160

6 0.5 0.8 1.7 3.1 7 10 10 10 10

10 1.4 2.3 3.4 4.8 7.5 10 10

13 2.3 3.4 4.8 7.5 10 10

16 2.0 2.9 4.2 6 9.5 10

20 2.7 3.8 5.6 8.5 10

25 3.6 5.4 8 10

32 4.2 6.8 10

40 4.2 6.8 9.5

50/63 no selectivity 5.7 8.5

‘D’ CharacteristicMCBs Fuse sizes

InA 20 25 35 50 63 80 100 125 160

6 0.7 1.7 3 5.9 6 6 6 6

10 1.3 2.2 3.6 6 6 6 6

13 1.7 2.5 4 6 6 6

16 1.6 2.2 3.1 4.6 6 6

20 2.2 3.1 4.6 6 6

25 3.1 4.6 8 6

32 2.6 3.5 6 6

40 3.5 6 6

40/50 5.5 6

63 no selectivity

MAXIMUM EARTH FAULT LOOP IMPEDANCESZs (Ohms) for µo=230V~➀

Rating B Characteristic C Characteristic D Characteristic(A) to<0.4s to<5s to<0.4s to<5s to<0.4s to<5s

6 7.6 7.6 3.8 5.9 2.7 3.6

8 2.8 5.7 2 2.7

10 4.6 4.6 2.3 3.5 1.6 2.9

16 2.9 2.9 1.4 2.2 1 1.8

20 2.3 2.3 1.1 1.7 0.8 1.4

25 1.8 1.8 0.9 1.4 0.6 1.1

32 1.4 1.4 0.7 1.1 0.5 0.9

40 1.1 1.1 0.6 0.9 0.4 07

50 0.9 0.9 0.5 0.7 0.3 0.6

63 0.7 0.7 0.4 0.6 0.25 0.46

➀ µo = rated voltage to earthed conductors for µ0=240v~ Zs•1.04 applies.

DISCRIMINATION

The Wiring Regulations require (533-6) that ‘the characteristics andsettings of devices for overcurrent protection shall be such that properdiscrimination in their operation is assured’. At overload levels acomparison of the devices’ time/current characteristics will showwhether discimination is acheived. For example, the relationshipbetween MCBs as final circuit devices, and cartridge fuses may besummarised.

SHORT CIRCUIT DISCRIMINATION LEVELS

PROSPECTIVE FAULT CURRENT

Given proper design of an installation the 10kA rating ofLoadlimiter MCBs means that they will deal with prospective faultcurrents up to 10,000 amps without the need for additional backup protection. In addition, faults rarely occur at the board itself and are mostlikely at points remote from the board where prospective current

is reduced considerably by the fault loop impedance. In a typical breaking operation when the prospective fault current is10,000 amps, the combination of forced contact separation and rapidarc extinction produces a limiting effect on the fault current so that itnever reaches the prospective peak value.

24

Load

limit

er M

CB

s -

Cha

ract

eris

tic

Cur

ves

25

Loadlimiter R

CB

O/R

CC

B - Technical Inform

ation

1 1.5 2 3 4 5

3 5

6 8 10 15 20 300.01

0.02

0.04

0.06

0.1

0.2

0.4

0.6

1

2

46

10

20

401

2

4

6

10

20

40

60

120

Tri

ppin

g tim

e

Min

utes

Seco

nds

1.13 1.45

a.c.

d.c.

7

Multiple of rated current

1 1.5 2 3 4 5

5

6 8 10 15 20 300.01

0.02

0.04

0.06

0.1

0.2

0.4

0.6

1

2

46

10

20

401

2

4

6

10

20

40

60

120

Tri

ppin

g tim

e

Min

utes

Seco

nds

1.13 1.45

a.c.

d.c.

10 14

Multiple of rated current

1 1.5 2 3 4 5 6 8 10 15 20 300.01

0.02

0.04

0.06

0.1

0.2

0.4

0.6

1

2

46

10

20

401

2

4

6

10

20

40

60

120

Tri

ppin

g tim

e

Min

utes

Seco

nds

1.13 1.45

10

Multiple of rated current14

ac

dc

21

‘C’ Characteristic

‘D’ Characteristic

‘B’ Characteristic

LOADLIMITER MCB TRIPPING CHARACTERISTICS

70 6443.5

354590

70

3564

6

43.5

35 4590

69.5

45

43.5

3590

30.568

97

3517.5

6000

4000

2000

1000

600400

200

100

6040

20

10

64

2

1

0.60.4

0.2

0.1

0.060.04

0.02

0.01

0.005

1 1.5 2 3 4 5 6 7 8 10 15 20

6000

0.5 1 2 3 5 10

3600

2000

1000

600400

200

100

6040

20

10

64

2

1

0.60.4

0.2

0.1

0.060.04

0.02

0.010.0060.005

LOADLIMITER RCCB TECHNICAL SPECIFICATIONS

LOADLIMITER RCBO TECHNICAL SPECIFICATIONS

RCBO Residual Current (RCCB)

RCBO Overcurrent (MCB) Type ‘C’Conforms to BS EN 61009

Voltage - 127V – 240V ac 50/60Hz

Primary current - 6A-40A

Residual sensitivity - 10mA, 30mA

Short circuit capacity - 10mA-6kA- 30mA-10kA

Terminal capacity (all ratings) - 10mm2 (top terminals)- 25mm2 (bottom terminals)

Conforms to BS EN 61008

Voltage - 240/415V ac 50/60Hz

Primary current - 40A, 63A, 100A

Residual sensitivity - 30mA, 100mA, 300mA

Terminal capacity - 40A-63A: 25mm2

- 100A: 35mm2

TECHNICAL SPECIFICATIONS

Conforms to BS EN 60898

Voltage - 230/400V ac60V dc per pole (max. 110V)

Reference calibration temp. - +30°C

Maximum operating temp. - +55°C

Current Range - B: 6A-63A (10 ratings)- C: 0.5A-63A (16 ratings)- D: 0.5A-63A (17 ratings)

Rated breaking capacity - B: 10kA- C: 10kA- D: 6kA

Terminal capacity - 0.5-40A: 25mm2

- 50 & 63A: 35mm2

Max. tightening torque - 2Nm (main terminals)- 0.5Nm (auxiliary terminals)