EPC 16 - Earthing System & Fault Loop Impedance

Question 1

Is it necessary to earth metallic boxes which form part of a wiring system if they are isolated from all other conductive material (other than metal which is earthed), and in no part accessible to personal contact? (Give the Wiring Rules Clause Number).

Answer 1

No.

AS/NZS 3000 Clause 5.4.1.1 and 1.4.62.

Question 2

Is it permissible to install an all insulated luminaire (such as an insulated batten holder) indoors without providing an earthing conductor at the lighting point? (Give the Wiring Rules Clause Number).

Answer 2

No.

AS/NZS 3000 Clause 5.4.3.

Question 3

Is it necessary to earth accessible metal parts of low voltage equipment if the accessible metal is separated from live parts by double insulation? (Give the Wiring Rules Clause Number).

Answer 3

No.

AS/NZS 3000 Clause 5.4.1.1 Exception.

Question 4

What is the internationally recognised symbol which means ‘Double insulated - Do not earth’?

Answer 4

One square inside another.

Question 5

What precaution must be taken to prevent an internal conductor from coming into contact with accessible metal if it becomes detached from its terminal in a double insulated appliance?
(Give the Wiring Rules Clause Number).

Answer 5

Clause AS/NZS 3000 5.4.1.1 Exception (c).
It must be protected, secured or insulated so that it (or its single insulation) cannot come in contact with accessible metal.

Question 6

Is it necessary to earth exposed metal in a 32V portable hand-lamp?
(Give the Wiring Rules Clause Number).

Answer 6

No.

AS/NZS 3000 Clause 5.4.1.1.

Question 7

Is it permissible to loop a MAIN earthing conductor into a luminaire to avoid having to run another earthing conductor to the luminaire?
(Give the Wiring Rules Clause Number).

Answer 7

No.

AS/NZS 3000 Clause 5.5.1.1.

Question 8

Is it permissible to connect a subsidiary earthing conductor to a main earthing conductor using a soldered tee joint?
(Give the Wiring Rules Clause Number).

Answer 8

Yes.

AS/NZS 3000 Clause 5.5.2.1(b) and 3.7.2.11

Question 9

Is it permissible to earth equipment by connecting exposed metal to an earthing conductor which is being used to earth equipment supplied from another distribution board? (Give the
Wiring Rules Clause Number).

Answer 9

No.

AS/NZS 3000 clause 5.5.2.1(c) and 5.5.2.2.3.

Question 10

What is the minimum permissible size of a single insulated TPI copper main earthing conductor?
(Give the Wiring Rules Clause Number).

Answer 10

The minimum permissible size of main earthing conductor is 4mm?.
AS/NZS 3000 Clause 5.3.3.2.

Question 11

A steel wire armoured (SWA) cable is installed in such a way that the armouring is required to be earthed. At which point in the installation must the armouring be earthed? (Give the Wiring
Rules Clause Number).

Answer 11

It must be earthed at the end adjacent to the switchboard or at which the cable originates.
AS/NZS 3000 Clause 5.5.3.2(b).

Question 12

What limitation is placed on the use of metal conduit as the protective earthing conductor for cables which are contained in the conduit?
(Give the Wiring Rules Clause Number).

Answer 12

The metallic enclosure and associated fittings must be electrically and mechanically continuous.
AS/NZS 3000 Clause 5.5.4.2.

Question 13

A particular electric motor is to be fixed in position using four bolts with nuts. Is it permissible
to use one of the fixing bolts as the earthing terminal?

Answer 13

No.

AS/NZS 3000 Clause 5.5.6.2(d).

Question 14

In general, where must a driven earth electrode be located? (Give the Wiring Rules Clause
Number).

Answer 14

Exposed to the weather; outside the building; separated from metallic enclosures of other buried surfaces.
AS/NZS 3000 Clause 5.3.6.4(a) (b).

Question 15

What is the general meaning of the term ‘equipotential bonding’? (Give the Wiring Rules
Clause Number).

Answer 15

The electrical connection of non-electrical metallic piping to the main earth in an installation.
AS/NZS 3000 Clause 1.4.60 and 5.6.

Question 16

What is the minimum permissible size of copper equipotential bonding conductor? State the AS/NZS 3000 clause number.

Answer 16

4mm

AS/NZS 3000 Clause 5.6.3.2.

Question 17

FILL IN THE BLANK

Any situation which is external to a building and within ________ Of exposed earthed metal is deemed to be an earthed situation.
(Give the Wiring Rules Clause Number).

Answer 17

2.5m AS/NZS 3000 Clause 1.4.48.

Question 18

What are two requirements for an effective earth joint? (Give the Wiring Rules Clause Number).

Answer 18

Joints must be mechanically and electrically sound. AS/NZS 3000 Clause 3.7.1.

Question 19

Is it necessary to earth the metal frame of a domestic installation? (Give the Wiring Rules Clause Number).

Answer 19

Yes. AS/NZS 3000 Clause 5.4.6.1.

Question 20

What is the main reason why single insulated 230V equipment must be earthed?

Answer 20

To provide a mechanism for automatically disconnecting the supply in the case of a short circuit
to earth.

Question 21

An EARTHED SITUATION is where there is a reasonable chance of a person touching __________ and at the same time coming in contact with an earth. (Give the Wiring Rules Clause Number).

Answer 21

Exposed metal AS/NZS 3000 Clause 1.4.48.

Question 22

List the internal and external parts of an MEN system which comprise the ‘fault-loop’ according to AS/NZS 3000.
(Give the Wiring Rules Clause Number).

Answer 22

Protective earth.
Earth bar
MEN link 
Neutral Bar  
Protective Earth Neutral. 
Transformer winding 
Consumer Mains 
Associated FSC active to fault. 
AS/NZS3000 Clause B4.4.