Part P BS 7671 IET Wiring Regulations 3 — Questions and Answers
Question 1: What does 'IP rating' mean for electrical equipment?
- Ingress Protection — the degree of protection against solid objects and water, coded by two digits (e.g., IP44) (Correct answer)
- Installation Pressure rating
- Internal Protection rating
- Inspection and Preventative maintenance rating
Correct answer: Ingress Protection — the degree of protection against solid objects and water, coded by two digits (e.g., IP44)
IP (Ingress Protection) ratings classify the degree to which electrical equipment is protected against solid particles and liquids; the two digits indicate protection levels against solids and water respectively.
Question 2: What minimum IP rating is required for electrical accessories in a bathroom Zone 1 (above the bath rim)?
- IPX4 (splash-proof) (Correct answer)
- IPX0 (no protection)
- IPX7 (temporary immersion)
- IPX2 (dripping water)
Correct answer: IPX4 (splash-proof)
BS 7671 requires a minimum of IPX4 (protection against water splashing from any direction) for electrical equipment installed in bathroom Zone 1, between the rim of the bath and 2.25 m above floor level.
Question 3: Which document supplements BS 7671 with guidance on regulations and is commonly used alongside it?
- The IET Guidance Notes (GN1–GN8) and the On-Site Guide (Correct answer)
- The Building Regulations Approved Documents
- The Electrician's Guide to the Building Regulations
- HSE Guidance HSG85
Correct answer: The IET Guidance Notes (GN1–GN8) and the On-Site Guide
The IET Guidance Notes (GN1 to GN8) and the IET On-Site Guide provide practical guidance on complying with BS 7671 and are widely used by installers alongside the main regulations.
Question 4: What is the purpose of Appendix 3 of BS 7671?
- To provide time/current characteristics of overcurrent protective devices for use in calculations (Correct answer)
- To list cable types
- To specify earthing system requirements
- To provide certification forms
Correct answer: To provide time/current characteristics of overcurrent protective devices for use in calculations
Appendix 3 of BS 7671 provides time/current characteristics graphs for fuses and circuit breakers, which are used to verify that protective devices will disconnect within the required time under fault conditions.
Question 5: What is meant by 'diversity' in electrical installation design?
- The allowance that not all loads will be in use simultaneously, allowing the main supply cable to be sized below the sum of all connected loads (Correct answer)
- Using different cable types in the same installation
- Installing multiple consumer units
- Connecting loads to different phases
Correct answer: The allowance that not all loads will be in use simultaneously, allowing the main supply cable to be sized below the sum of all connected loads
Diversity accounts for the fact that not all connected loads operate simultaneously at full load; it allows supply cables and switchgear to be sized realistically rather than for the full theoretical maximum demand.
Question 6: What is a 'circuit protective conductor' (CPC)?
- The earth (green/yellow) conductor that connects exposed conductive parts of equipment to the main earthing terminal for fault protection (Correct answer)
- The neutral conductor
- The phase conductor
- The bonding conductor connecting metalwork
Correct answer: The earth (green/yellow) conductor that connects exposed conductive parts of equipment to the main earthing terminal for fault protection
The CPC (earth conductor, identified by green/yellow insulation) connects the exposed metalwork of electrical equipment back to the main earthing terminal, providing a low-impedance path for fault current to operate the protective device.
Part P BS 7671 IET Wiring Regulations 3
What does 'IP rating' mean for electrical equipment?