MCB selection guide

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MCBs

MCB is a generic term for modular circuit -breakers designed to EN 60898-1. For use in domestic and similar installations under the control of "Ordinary Persons".*

BS7671 maximum Zs values for 0.4s (Table 41.3) and time/current characteristics (Apx 3) relate to circuit-breakers to EN 60898-1.

Standard characteristics for ratings < 63A

Instantaneous Tripping Range EN 60898-1

Characteristic

Range

B

>3 In < 5 In

C

>5 In < 10 In

D

>10 In < 20 In


Sustained overcurrent condition EIV60898-1:

In

State

Time

Result

1.13

Cold

t < 1 h

No Trip

1.45

Hot

t < 1 h

Trip


Note: Associated devices and cables must be rated to carry the total sustained overcurrent. Refer to IET Guidance Note 6 - see below.

*Circuit-breakers designed to EN60947-2 are for use in installations under the control of skilled persons. For selection refer to Regulation 411.4.202.

IET wiring regulations

IET Wiring Regulations (BS7671) specify where and when overcurrent protection must be provided – see Chapter 43:

IET Guidance Note 6 provides additional guidance and advice on the requirements for overcurrent protection.

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MCB Power Dissipation

Panel design verification to EN61439-1

  • 10.10.2 Verification of temperature rise

Prototype design calcualtions before testing and actual assembly.

  • 10.10.4 Verification by assessment

Calculation based on a reference design.

MCB Temperature

MCB Temperature EN60898-1 specifies the reference temperature for MCBs at 30 C.

This is the ambient temperature immediately surrounding the MCB.

Increase or decrease in temperature results in a change to the tripping characteristics.