Sample questions and answers 2391 theory exam.

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An installation has been seriously overloaded and needs investigation. State the
(a) type of inspection and test that would be required.
(b) Documentation that will need to be completed.

(a) Periodic inspection and test
(b) Periodic Inspection Report including an Inspection Schedule and a Test Schedule

State the
(a) statutory document that is relevant to inspection and testing
(b) non-statutory document that is relevant to electrical test equipment
(c) non-statutory document that is relevant to The Requirements for Electrical Installations

(a) Electricity at Work Regulations 1989
(b) HSE GS38
(c) BS7671 2001

State the person who should
(a) decide when the first periodic test on an installation should be carried out
(b) decide when later periodic tests on an installation should be carried out
(c) agree with the inspector the extent and limitations of a periodic inspection and test

(a) Designer
(b) Inspector
(c) Client

State the form of protection that is offered by each of the following
(a) placing out of reach
(b) SELV

(a) protection against direct contact
(b) protection against direct and indirect contact

State the instrument required for each of the following tests
(a) continuity of protective conductors
(b) insulation resistance
(c) live polarity

(a) low resistance ohmmeter
(b) insulation resistance ohmmeter
(c) approved voltage indicator

State 3 circumstances that would result in an increase in conductor resistance

Increase in conductor temperature due to overload
Increase in conductor temperature due to fault current
Increase in conductor temperature due to an increase in ambient temperature
Reduction of csa
Increase in conductor length

The continuity of a lighting circuit protective conductor is to be tested. If the test method uses a temporary link between phase and earth in the distribution board, state
(a) at which points in the circuit the test should be conducted
(b) the conductors between which the tests should be made
(c) the significance of the test reading at the end of the circuit

(a) at each point
(b) phase and cpc
(c) R1+R2 for the circuit

The steel conduit of an installation is used as the cpc. State the three stages of the test that may b needed to check its continuity.

Actually, there are 4 stages;
Thorough inspection along its length
Test with a low resistance ohmmeter
Test with an earth loop impedance tester
May require a further test using a low resistance high current ohmmeter (output 50vac with a test current circa 25 amps)

For a ring final circuit wired in p.v.c. twin with c.p.c. state the
(a) instrument used to conduct a continuity test
(b) reason why phase to c.p.c. readings at each socket increase slightly to the mid point of the ring then decrease again
(c) other test that is automatically conducted

(a) low resistance ohmmeter
(b) difference in c.s.a and therefore resistance
(c) polarity

The insulation of a 600v discharge lighting installation is to be tested. State
(a) test instrument to be used
(b) test voltage to be applied
(c) minimum value of insulation resistance

(a) Insulation resistance ohmmeter
(b) 1000v dc
(c) 1megohm

For an insulation resistance test on a 230v installation. State the
(a) minimum value of resistance acceptable
(b) value below which, further investigation is required
(c) minimum value of each circuit due to (c) above

(a) 0.5 megohm
(b) 2 megohm
(c) 2 megohm

For an installation in a bathroom, state the
(a) type of socket outlet permitted excluding shaver sockets
(b) location of zone 1
(c) maximum rating of an rcd protecting a shower circuit

(a) SELV
(b) Within the bathtub or shower basin
(c) None stated in BS7671 but presumably it will provide supplementary protection against direct contact, thus 30ma is maximum.

State the IP codes which should apply to each of the following
(a) accessible top surfaces of enclosures
(b) an intermediate barrier inside an enclosure

(a) IP4X
(b) IP XXB

State the three main reasons for conducting a polarity test on a new installation prior to it being energised.

To ensure that all single pole devices are connected in the phase conductor only
To ensure that the centre contact of ES lampholders are connected to the phase conductor only
To ensure the correct connection of accessories and socket outlets

The total loop impedance of a circuit may be calculated using the external loop impedance, the length and milliohm resistance of the circuit conductors, and a correction factor of 1.2 for operating temperature. State the formula used

Zs = Ze + (R1 + R2) x 1.2 / 1000

State the
(a) important check to be made regarding equipotential bonding conductors before carrying out a loop impedance test on a circuit
(b) action to be taken regarding the earthing conductor prior to conducting an external loop impedance test
(c) precaution to be taken before conducting the test at (b)

(a) You used to have to disconnect them. NO LONGER REQUIRED
(b) Should be disconnected from MET
(c) Isolate installation

A test is to be conducted on a lightning conductor earth electrode. State the
(a) instrument to be used
(b) names of the other two electrodes to be used in the test

(a) Earth electrode resistance tester
(b) Potential spike. Current spike

State three reasons for the use of a 500ma rcd in an installation

To provide protection against INDIRECT contact
To provide a measure of protection against fire
To help reduce nuisance tripping where protective conductor currents are present

State
(a) why a test on an rcd must not be conducted before a loop impedance test
(b) the maximum test current to be applied to a 10ma rcd used as supplementary protection against direct contact
(c) the maximum test current that needs to be applied to a 100ma rcd

(a) The earth loop must be low enough to ensure that the rise in voltage due to test current injected to test the rcd will not cause dangerous voltages to occur between installation earthed metalwork and earth.
(b) 50ma
(c) 100ma

A single phase TN-C-S installation has a measured value of external loop impedance of 0.015ohms. Show by calculation the expected value of prospective fault current at the origin.

Ipfc = Uo / Ze. Thus a prospective fault current of circa 16Ka can be expected at this point.

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