MOCK EXAM from past papers - No. 2

16) If Ze is measured at 0.68Ω and R1+R2 is measured at 0.82Ω, the value of Zs would be
a) 2.88Ω
b) 0.18Ω
c) 1.5Ω
d) 0.5Ω

17) The maximum Zs for a 16A Type B circuit breaker protecting a fixed appliance is
a) 1.87Ω
b) 0.87Ω
c) 2.4Ω
d) 2.73Ω

18) In a TT installation, distribution circuits must satisfy a disconnection time of
a) 4s
b) 1s
c) 0.5s
d) 0.2s

19) In domestic installations where circuits are protected by RCD's, the product of the earth fault loop impedance and the rated residual operating current of the device must not exceed
a) 20v
b) 50v
c) 110v
d) 120v

20) A residual current device works by a) a magnetic device operating in the event of a fault between live and earth
b) a magnetic device operating in the event of a fault between neutral and earth
c) a thin element operating in the event of a fault between neutral and earth
d) a thin element operating in the event of a fault between live and earth

21) An electrical installation certificate should be signed by
a) the customer
b) the local authority
c) the REC
d) a competent person

22) Taking into account the presence of water, electrical installations installed outside in caravan park shall have minimum IP rating of
a) IP5X
b) IPX4
c) IP3X
d) IPX2

23) A Residual Current Device offers protection against
a) basic contact
b) overload current
c) earth fault current
d) short circuit current

24) In a TN system, the maximum earth fault loop impedance Zs when using a 32A, type B circuit breaker for instantaneous operation would be
a) 1.15 ohms
b) 1.09 ohms
c) 1.37 ohms
d) 0.72 ohms

25) If a fault occurs in the HV system and a magnitude of fault voltage of 430v occurs between exposed conductive parts and earth on the LV installation, what is the maximum tolerable duration of the fault
a) 10ms
b) 100ms
c) 200ms
d) 300ms

26) If a line conductor of an IT system is accidentally, the insulation and components rated for the line to neutral voltage can be temporarily stressed with a higher voltage. What value can this stress voltage reach up to
a) U=√3 UO
b) U=3 UO
c) U=√ UO
d) U=UO

27) Copper cored data communication cables are made up of twisted pairs in order to
a) reduce manufacturing costs
b) speed the manufacturing process
c) reduce interference
d) increase core capacity

28) In a high rise building, lightning conductors must be bonded to the
a) earth electrode
b) structural steelwork
c) main incoming services
d) installation earth

29) Nuisance tripping from a large transformer installation can be prevented by
a) the use of an RCD
b) the use of a C Type MCB
c) the use of a B Type MCB
d) the use of a D Type MCB

30) Where a clamp is used for bonding purposes, a permanent label shall be fixed in a visible position with the wording
a) danger electrical connection-do not remove
b) danger electrical connection-do not remove
c) safety earth connection-do not remove d
d) safety electrical connection-do not remove