The fundamental principles stated in BS 7671 for protection against overvoltage are given in Chapter
1. 13
2. 40
3. 47
4. 51
BS 7671 does NOT apply to
1. agricultural installations
2. caravan site installations
3. quarry site installations
4. horticultural installations.
An a.c. voltage of 120 V between conductors is classified as
1. ELV
2. LV
3. SELV
4. RLVS
Protection against direct contact can be achieved by
1. limiting the current which can pass through the body
2. ensuring all extraneous parts are at equal potential
3. automatic disconnection of the supply during earth fault conditions
4. separation of the supply and load by means of isolating transformer.
An example of an extraneous conductive part is
1. an electrical conduit
2. a metallic cable trunking
3. a metal clad fuse board
4. a metal sink.
In a supply classified as TN-C-S the
1. consumer provides their own earth electrode
2. supplier uses a combined protective and neutral conductor
3. consumer must use the main gas or water services as an earth
4. earth fault loop impedance is below 0.5 Ω.
An external influence categorised as AG1 applies to a
1. quarry
2. factory
3. house
4. workshop.
Type D circuit breakers to BS EN 60898 should be installed to protect circuits subjected to
1. transient overvoltages
2. a power factor of less than 0.85
3. fluctuating protective conductor currents
4. heavy starting currents.
An assessment MUST be made of the harmful effects upon other electrical services when installing
1. fluctuating loads such as welding transformers
2. automatic fire alarm circuits
3. emergency lighting circuits
4. SELV supplies.
For final radial circuits using 16 A socket outlets to BS EN 60309-2, the rating of the overcurrent protective device must NOT exceed
1. 16A
2. 20 A
3. 30 A
4. 32 A.
A final circuit is the wiring between the
1. supply company's fuse and the energy meter
2. main switch and distribution board
3. distribution board and current using equipment
4. supply company's fuse and remotest outlet point.
A 30 A ring final circuit installed in p.v.c. conduit is shown in Fig. 1. The number of single core cables to be run in the section marked A B is
1. 3
2. 4
3. 5
4. 6
Prior to the construction of a new electrical installation, the information to be given to the Local Electricity Supplier in order to establish the type and rating of supply is the
1. nature of current and frequency
2. nominal voltage
3. maximum demand
4. external impedance (Ze).
Which one of the following is NOT a characteristic of the supply?
1. Nominal voltage.
2. Frequency.
3. Earth loop impedance Ze
4. Emergency switching
An electric fire having an element exposed to touch would increase the risk of an electric shock by
1. prospective contact
2. earthing contact
3. indirect contact
4. direct contact.
By which one of the following methods can protection against direct and indirect contact be achieved?
1. SELV.
2. Insulation of live parts.
3. FELV.
4. Protection by non-conducting location
An extra-low voltage system which is electrically separated from earth and is supplied by a recognised safety source, is defined as
1. FELV
2. SELV
3. non-conducting
4. earth free.
BS 1363 socket outlets intended to supply equipment outdoors must be protected by an RCD having an I∆n NOT exceeding
1. 10 mA
2. 20 mA
3. 30 mA
4. 40 mA.
In order to comply with BS 7671, the maximum earth loop impedance for a 30 A BS 3036 fuse protecting an item of stationary equipment is
1. 2.40 Ω
2. 2.76 Ω
3. 2.93 Ω
4. 3.04 Ω
Where a 230 V installation forms part of a TN system, the maximum disconnection time is
1. 0.1 s
2. 0.2s
3. 0.4 s
4. 0.8 s.
One item of electrical equipment likely to need additional protection against thermal effects is a
1. fluorescent luminaire
2. tungsten filament lamp luminaire
3. single pole dimmer switch
4. consumer unit housing rewirable fuses.
Co-ordination between fuse ratings in an electrical system is termed
1. discrimination
2. isolation
3. diversity
4. overload.
If the mechanical load being driven by an a.c. motor became seized, the electrical protection for the circuit should operate. This condition is termed as
1. overload
2. short circuit
3. indirect contact
4. direct contact
The nominal rating of an overcurrent protective device should be
1. not less than the design current
2. greater than the current carrying capacity of the conductors
3. 1.45 times the load current
4. equal to the prospective short-circuit current.
When a stop button used for emergency switching is released
1. the circuit will be re-energised
2. the circuit will not be re-energised
3. the overload protection will operate
4. a warning light will indicate a fault on the circuit.
Where protection against undervoltage is required and the reclosure of a protective device is likely to cause danger, the reclosure shall
1. be performed by a skilled person
2. not be delayed
3. be automatic
4. not be automatic
The temperature limit for a non-metallic part of electrical equipment that is within arm's reach but need not be touched during normal operation is
1. 65°C
2. 70°C
3. 80°C
4. 90°C.
For overhead wiring between buildings in positions accessible to vehicles, the minimum height of span above ground is
1. 3m
2. 3.5 m
3. 5.2 m
4. 5.8 m.
The minimum permitted cross-sectional area of a supplementary bonding conductor connecting two extraneous-conducting parts and having mechanical protection is
1. 1.5 mm²
2. 2.5 mm²
3. 4.0 mm²
4. 6.0 mm².
Fig. 2 illustrates an installation in the premises of a small business. The minimum assumed current demand for this installation is
1. 49 A
2. 50 A
3. 51 A
4. 57.5 A.
Where the main earth terminal is separate from main switchgear, a permanent label shall be fixed in a visible position with the wording
1. Danger Electrical Connection - Do Not Remove
2. Safety Electrical Connection - Do Not Remove
3. Danger Earth Connection - Do Not Remove
4. Safety Earth Connection - Do Not Remove.
Where a person other than a skilled or instructed person is likely to replace a fuse link, it is a requirement that this cannot be replaced by a fuse link having
1. a lower nominal current but the correct fusing factor
2. the intended nominal current but a lower fusing factor
3. a higher nominal current but the correct fusing factor
4. the intended nominal current but a higher fusing factor.
The purpose of an equipotential bonding conductor is to
1. ensure that leakage current is minimised
2. ensure that the maximum fault current will flow to earth
3. reduce the possibility of shock risk within the premises
4. reduce the possibility of electrolytic corrosion.
Which one of the following is NOT recognised by BS 7671 as suitable for acting as an earth electrode?
1. Non-corrosive metallic coverings of cables.
2. Earth plates.
3. Underground structural metalwork embedded in foundations.
4. Gas and water supply pipes
Where practicable, the main equipotential bonding to the gas services in a building should be made within
1. 3 m of the meter on the supply side
2. 3 m of the meter on the consumer's side
3. 600 mm of the meter on the supply side
4. 600 mm of the meter on the consumer's side.
Where a residual current device is used in an installation, the product of its rated residual operating current and the earth fault loop impedance should NOT be greater than
1. 2V
2. 10V
3. 40 V
4. 50 V.
A 13 A socket-outlet, connected directly to a TN-C-S system, supplies portable equipment for use outdoors. Supplementary protection to reduce direct contact risk should be provided by means of a
1. general purpose fuse
2. miniature circuit breaker
3. residual current device
4. class II equipment enclosure.
The purpose of the integral test button of a residual current device is to check the
1. continuity of the earthing conductor
2. earth fault loop impedance
3. earth electrode resistance
4. mechanical parts of the device
A device for protection against fault current shall be placed at the point where
1. current-using apparatus or appliances are normally connected
2. a reduction occurs in the current carrying capacity of conductors
3. a conductor connects a transformer with its control panel
4. the supplier installs a metering device.
Control equipment incorporating overcurrent protection must be installed with every electric motor having a rating exceeding
1. 0.37 kW
2. 0.5 kW
3. 1.0 kW
4. 2.0 kW.
The circuit of a safety service shall be
1. coloured red
2. independent of any other circuit
3. housed in compartmentalised trunking
4. un-protected.
Where an installation and generator are not permanently fixed, protection against indirect contact must be provided by the use of a residual current device. The rated residual current (IAN) of such a device must not exceed
1. 10 mA
2. 30 mA
3. 100 mA
4. 500 mA.
In Zone 2 of a bathroom, wiring systems embedded in the walls at a depth not exceeding 50 mm shall be limited to those which supply fixed equipment in Zones
1. 1 and 3
2. 0,1and 2
3. 0,2and 3
4. 1,2 and 3.
If a socket outlet has to be installed in Zone B of a small swimming pool, it must conform to
1. BS EN 60898
2. BS 1363
3. BS 6991
4. BS EN 60309-2.
Other than within site offices, toilets etc., every plug and socket outlet for use on a construction site shall comply with
1. BS EN 60309-2
2. BS EN 60947-2
3. BS EN 60947-3
4. BS EN 60269-1.
In agricultural and horticultural installations, electrical equipment installed for normal use shall have a minimum degree of protection to
1. IP22
2. IP33
3. IP44.
4. IP55.
In a touring caravan, a notice indicating the nominal voltage, frequency and rated current of the caravan installation must be fixed
1. inside the fuse box
2. on or near the inlet recess
3. on or near the front window
4. on the towbar.
To reduce the risk of shock from the metalwork of Class I street located equipment, protection should be by
1. non-conducting location
2. EEBAD
3. earth-free equipotential bonding
4. electrical separation.
The minimum cross-sectional area of the protective conductor used within a final circuit, having high protective conductor currents in excess of 10 mA when supplying more than one item of electrical equipment, may be 4 mm2, provided that a
1. additional protection from the use of a residual current device is present
2. the protective conductor has additional mechanical protection
3. individual items of equipment are supplied through an isolating transformer
4. the protective conductor is in the form of a complete ring.
When carrying out a detailed inspection, which one of the following must be verified?
1. The presence of fire barriers and protection against thermal effects.
2. The prospective short circuit current at the origin.
3. The maximum permissible voltage drop.
4. The actual voltage drop.
A legible diagram, chart or table relating to an installation must be provided to indicate
1. the location of all fixed equipment for testing purposes
2. any circuit of equipment vulnerable to a typical test
3. the location of all portable equipment for testing purposes
4. that the original installation design has not changed.
The MINIMUM size of trunking required to enclose ten 6 mm² and twenty 10 mm² single-core thermoplastic (p.v.c.) cables is
1. 50 x 38 mm
2. 100 x 25 mm
3. 100 x 50 mm
4. 100 x 100 mm.
Which one of the following items must be included in a test sequence?
1. Identification of conductors.
2. Protection against indirect contact.
3. Adequacy of access to switchgear.
4. Operation of an r.c.d.
An insulation resistance test set used to carry out an insulation test on a 400 V circuit MUST be capable, when loaded with 1 mA, of supplying a test voltage of
1. 400 V
2. 500 V
3. 1000 V
4. 3750 V.
It should be verified that any addition to an existing installation has
1. a supply separate from that of the existing installation
2. a similar wiring system to that used in the existing installation
3. been treated as being entirely separate from the existing installation
4. not impaired the safety of the existing installation.
The results of Periodic Inspection and Testing should be recorded on a Periodic Report Form and signed by
1. the person ordering the inspection
2. a design engineer
3. a site engineer
4. a competent inspector.
The frequency of Periodic Inspection and Testing of an installation should be determined by
1. an agent or representative of the original installer
2. the type, use and operation of the installation
3. the owner of the building in which the installation is situated
4. the local Electricity Supply Company.
A 30 A semi-enclosed fuse to BS 3036 has a fault current of 300 A. The disconnection time will be
1. 0.02 s
2. 0.2 s
3. 2.0 s
4. 200 s.
The external influence having a classification of AD7 indicates
1. humidity
2. immersion in water
3. dust in the atmosphere
4. high levels of vibration.
A trunking is required to carry the cables of six three-phase circuits. Which one of the following is the grouping factor to be used when determining the size of the conductors?
1. 0.39.
2. 0.45.
3. 0.57.
4. 0.69.

City & Guilds 2381 - Sample Paper 3