303 #8 – Design Current & Devices

What does Ib stand for in design calculations?

• Installation backup

• Insulation barrier

• Design current

• Current at the board

What is In in a protective device context?

• Current rating of the protective device

• Instantaneous tripping current

• Insulation neutral

• Internal resistance

What is the minimum requirement for Iz in relation to Ib and In?

• Iz must be less than Ib

• Iz must be equal to Ze

• Iz must be greater than or equal to In

• Iz must be half of Ib

Why is diversity applied to electrical designs?

• To increase volt drop

• To reduce the design current

• To raise insulation levels

• To size smaller protective devices

Which table in the On-Site Guide is used for diversity factors?

• Table A2

• Table 1.2

• Table 1A

• Table B3

If a cooker has a rated current of 32A, what current might you apply after diversity?

• 50A

• 32A

• Around 10A

• 2A

What does the formula Ib ≤ In ≤ Iz ensure?

• The protective device is oversized

• The cable will never overheat

• The Ze value is correct

• The insulation is non-flammable

A 6mm² T&E cable is being considered for a 32A circuit. What must you confirm?

• That it looks neat

• That Iz is at least 32A

• That the trunking is steel

• That the RCD is type A

If a lighting circuit has 10 luminaires at 100W each, what is Ib?

• 0.5A

• 10A

• 1A

• 100A

Which regulation in BS7671 governs protective device coordination with current-carrying capacity?

• Reg 411.3.1.2

• Reg 433.1.1

• Reg 132.2

• Reg 514.8.2