Practise for the 18th Edition 2382-26 exam.

Try 8 practice questions for the 18th Edition

Real questions from electriQual on equipment classes and earth fault loop paths, including PNB, an earthing arrangement that appears in BS 7671 for the first time with Amendment 4. Pick your answer, then open it to check.

1. from "Class I equipment"

   An appliance has a metal case connected to earth through a CPC. Which class is it?

   1. AClass I
   2. BClass 0
   3. CClass II
   4. DClass III
   Show the answer

   A. Class I

   In Class I equipment, the metal parts you can touch are connected to a means of earthing through the CPC.

2. from "Class II equipment"

   A drill has two layers of insulation and no earth wire. Which class is it?

   1. AClass I
   2. BClass 0
   3. CClass II
   4. DClass III
   Show the answer

   C. Class II

   Class II equipment is protected by double insulation, and it has no CPC.

3. from "Class III equipment"

   A piece of equipment is powered from a SELV supply. Which class is it?

   1. AClass I
   2. BClass III
   3. CClass II
   4. DClass 0
   Show the answer

   B. Class III

   Class III equipment protects you from shock by running at extra-low voltage. SELV, PELV and FELV are examples.

4. from "The earth fault loop path"

   Which part of the loop is different between earthing systems?

   1. AThe way out to the fault
   2. BThe fault itself
   3. CThe line conductor resistance
   4. DThe way back to the source
   Show the answer

   D. The way back to the source

   The only bit that changes between systems is the way back. The way out is the same every time.

5. from "The loop in a TN-S system"

   In TN-S, what does fault current travel back along?

   1. AThe combined neutral and earth conductor
   2. BThe general mass of earth
   3. CA separate metal earth conductor from the supplier
   4. DThe customer's earth electrode
   Show the answer

   C. A separate metal earth conductor from the supplier

   In TN-S the supplier gives you a separate metal earth conductor that runs all the way back to the source.

6. from "The loop in TN-C-S (PME)"

   What does the PEN conductor do?

   1. AIt acts as both the neutral and the earth in the supply
   2. BIt carries fault current only
   3. CIt is your earthing conductor
   4. DIt bonds the extraneous parts together
   Show the answer

   A. It acts as both the neutral and the earth in the supply

   In TN-C-S the supplier combines neutral and earth into one conductor, called the PEN.

7. from "The loop in TN-C-S (PNB)"

   How is PNB different from PME?

   1. AThe neutral is never earthed
   2. BIt is a TT system
   3. CThe customer fits their own electrode
   4. DThe neutral is earthed at one point instead of several
   Show the answer

   D. The neutral is earthed at one point instead of several

   In PNB the neutral is earthed at one single point, instead of at lots of points along the network.

8. from "The loop in a TT system"

   Why does a TT electrode resistance change over time?

   1. AThe load on the installation
   2. BSoil conditions and weather
   3. CThe main switch rating
   4. DThe length of the tails
   Show the answer

   B. Soil conditions and weather

   Soil and weather change the electrode resistance.