Earthing Systems

Question 1

What is earthing?

Answer 1

Connecting the power to earth for it do dissipate.

Question 2

Electricity will always find the ________ to earth.

Fill the blank.

Answer 2

“Shortest route”.

Question 3

Who provides earthing?

Answer 3

The distributor (the grid) unless it’s a TT system.

Question 4

Can the distributor refuse to supply an earth? If yes why

Answer 4

Yes , for safety reasons.

Question 5

Do you need to have an earth?

Answer 5

Yes, it is a legal requirement.

Question 6

What can you do if there is no earth provided?

Answer 6

Put an earthing rod in.

Question 7

What can we measure against earth.

Answer 7

Earth is a reference point for us to measure voltage.

Question 8

What are some advantages of earthing?

Answer 8

1. The whole electrical system will be tied to 0 volts
2. By connecting earth to any metal it will be protected against earth faults.

Question 9

What are some disadvantages of earthing?

Answer 9

1. Cost - adding an earth is very expensive.
2. Possible safety hazard. It has been argued that earth just created more places for the current to flow when there is a fault.

Question 10

What are the 5 types of earthing arrangements listed by the regulations?

Answer 10

1. TT - Tera Tera
2. TN-S - Tera Neutral Separated
3. TN-C-S - Tera Neutral Separated combined
4. IT - Isolated Tera
5. TN -C - Tera Neutral Combined

Question 11

What type of earthing is a TT system?

Answer 11

An earth electrode (rod).

Question 12

What type of earthing system do you connect an earth electrode / rod to.

Answer 12

TT systems.

Question 13

When do you use a TT earthing system?

Answer 13

When there is no earthing provided by the distributor.

Question 14

What is the maximum earth loop impedance (Zs) of a TT system?

Answer 14

200Ω.

Question 15

Is a TT system connected via an overhead, underground supply or both?

Answer 15

Overhead only.

Question 16

Where is TT earthing mostly found?

Answer 16

At farms

Question 17

What type of earthing system is TN-S?

Answer 17

When the earth is connected via a separate conductor. Usually via the metal sheath of the supply cable

Question 18

What type of earthing system do you connect the earth to the metal of the incoming cable?

Answer 18

TN-S

Question 19

Is a TN-S system connected via an overhead, underground supply or both?

Answer 19

Both

Question 20

What is the maximum earth loop impedance (Zs) of a TN-S system?

Answer 20

0.80Ω

Question 21

Where should the earthing conductor go to in a TN-S system

Answer 21

Straight to the consumer unit

Question 22

What type of earthing is a TN-C-S system?

Answer 22

When the earthing conductor comes off the fuse

Question 23

What type of earthing system is the earth conductor connected to the fuse?

Answer 23

TN-C-S

Question 24

What is the maximum earth loop impedance (Zs) of a TN-C-S system?

Answer 24

0.35Ω

Question 25

Is a TN-C-S system connected via an overhead, underground supply or both?

Answer 25

Both

Question 26

Where can’t TN-C-S systems be used?

Answer 26

Explosion risk areas like petrol stations.

Question 27

What does PME stand for?

Answer 27

Protective Multiple Earthing.

Question 28

What earthing system uses PME?

Answer 28

TN-C-S

Question 29

What does PNB stand for?

Answer 29

Protective Neutral Bonding.

Question 30

What is PME

Answer 30

Where the combined neutral and earth cable is connected to earth multiple times.

Question 31

How often is PME earthed?

Answer 31

Usually every 30 meters.

Question 32

Where can’t PME be used?

Answer 32

For temporary supply’s and supply’s to caravans and boats.

Question 33

What earthing system is banned and under what act?

Answer 33

TN-C under the electrical safety, quality and continuity regulation 2002 (ESQCR)

Question 34

Explain PNB

Answer 34

The neutral - earth connection is established just once near the installation