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2391-301 Written Exam Paper February 2012
Section B – Questions 21-26 refer to the following scenario. Answer
all questions. All questions carry equal marks. Show
all calculations.
The 400/240V three-phase, four-wire electrical installation within a three year old small industrial unit, forms part of a TN-S system and is to be inspected and tested during normal working hours.
The unit has a new tenant who requires an additional lighting circuit in the office area. The details of the protective devices utilised within the metal-clad TP&N distribution board are shown on Figure 1, attached.
The containment system within the workshop is surface mounted steel conduit and trunking. The office containment system is surface mounted PVC conduit and trunking.
All wiring is thermoplastic insulated single-core cables with copper conductors. The new lighting circuit is to be wired using the same installation method as the existing office.
The outside lighting circuits are controlled by a photo electric cell mounted on the roof of the installation.
21 State
a) the types of inspection and test that are required on completion of all of the works.
b) the documents that must be completed following this inspection and test.
c)
two statutory documents that are relevant to the inspection and testing process
d) the title given in law to the inspector whilst carrying out the inspection
e) the legal status of the inspector
f)
three items of information that must be available to the inspector which may be obtained from the DNO
22 a) identify
two specific items on a new containment system which are to be inspected, using the sense of touch, before the cables are installed, stating what is being checked for in
each case
b) identify
three items on the existing containment system which are to be inspected using the sense of sight stating what is being checked for in
each case
23 The existing ring final circuit in the workshop area is to be inspected. All socket outlets are connected correctly to the circuit. Step 1 of the test process produced the following results: Line loop 0.68Ohms, neutral loop 0.70Ohms and cpc loop 1.15Ohms.
a) state one possible reason why the cpc value is higher than the live conductors
b) calculate the expected measured values for steps 2 & 3 of the test
c) state all items that would be recorded following the successful completion of the test
d) under what circumstances would the ring final circuit continuity test
not be required during the inspection and test
e) for polarity to be confirmed, what action is required if the tests have taken place at the terminals of the socket outlet and not from the socket fronts?
24 An insulation resistance test is to be carried out on the outside security lights. Describe the procedure for this test.
25 Figure 1, attached, shows the results from a previous inspection and test. State, using the information in Figure 1 attached
a)
seven items which may require special consideration excluding equipment vulnerable to testing
b) the reasons why the items given in a) above are of concern
d) whether the equipment vulnerable to testing information is correct
26 Describe, with the aid of a fully labelled diagram, the earth fault loop impedance part for the new lighting circuit
