303 #5 – Overcurrent Protection

What is overcurrent?

• Current that flows through a lighting circuit

• Current that is less than the rated value

• Current exceeding the rated capacity of conductors or devices

• A low current in a ring circuit

Which of the following is a type of overcurrent?

• Low voltage

• Open circuit

• Short circuit

• Reverse polarity

What does an MCB protect against?

• High voltage

• Smoke

• Overload and short circuit

• Earth faults only

Which device provides time-delayed protection to allow discrimination?

• RCD

• Type D MCB

• Fuse wire

• SPD

What is meant by ‘discrimination’ in electrical design?

• Favouring certain circuits

• Avoiding electrical fires

• Ensuring only the faulty part of a system is disconnected

• Using only fuses

Which device typically operates fastest under fault conditions?

• Type B MCB

• Type C MCB

• Type D MCB

• BS88 fuse

Which document contains time/current curves for device selection?

• Manufacturer's data sheets

• OSG Appendix 1

• GN1

• NICEIC logbook

Which of the following is most important in achieving proper discrimination?

• Cable insulation

• Load schedule

• Selective tripping characteristics

• Conduit type

What chapter of BS7671 deals with protection against overcurrent?

• Chapter 41

• Chapter 52

• Chapter 43

• Chapter 54

If a protective device downstream trips before the upstream one during a fault, this is:

• A short circuit

• Correct discrimination

• Reverse flow

• A fault in the neutral