PR S 40023

Question 1

What is the purpose of insulation testing

Answer 1

to check for degradation or insulation defects which could potentially result in irregularities due to current leakage cutting out one or more control elements of a circuit.

Question 2

what are methods to detect electrical leakage paths

Answer 2

monitoring of busbars using earth leakage detectors
measuring busbars to earth using test instruments
testing conductor insulation with test instruments
function testing of signalling circuits
visual examination of cables etc.

Question 3

Responsibilities of signalling personnel regarding insulation testing

Answer 3

recording busbar to earth voltage, ELD testing and IR testing, visual inspection an reporting deterioration to the maintenance signal engineer

Question 4

What are the requirements for the insulation test instrument

Answer 4

Type approved/ calibrated and in date/ good working condition. 500VDC 3mA.

Question 5

What is the test earth normally used for insulation testing

Answer 5

the main earth bus in the location or a subsidiary earth bus bonded to the main earth.

Question 6

what must be done to the test earth before using it for testing

Answer 6

a check to prove the test earth is satisfactory by measuring the test earth to an alternative temporary test earth.

Question 7

what can the alternate earth used to check the test earth be

Answer 7

the ELD test earth, galvanised steel troughing, or a temporary electrode

Question 8

can you use the rail as a test earth

Answer 8

no

Question 9

what reading is ideal for a reference earth

Answer 9

less than 10k ohm, or a short circuit.

Question 10

what is to be conducted before insulation testing of cables

Answer 10

a visual inspection for damage or deterioration as far as practical. correlation and ensure test equipment is working properly.

Question 11

what needs to be done to replacement equipment before being installed

Answer 11

inspected to be in good condition and order

Question 12

what are the ideal conditions to insulation resistance test cables and where is it recorded

Answer 12

in wet or damp conditions. on the insulation test record sheets

Question 13

can wires or cable cores be removed from their terminals for testing

Answer 13

only when absolutely necessary, and only one wire should be removed at a time. the reconnection is to be tested.

Question 14

list some equipment to be disconnected before testing begins

Answer 14

transformers, surge arrestors, timers, electronic track circuit equipment, computer based interlocking equipment

Question 15

Should circuits be tested complete or in sections

Answer 15

the preference is divide circuits into internal wiring in locations, cables between locations and tail cables from trackside control equipment to trackside apparatus.

Question 16

what are the methods to inspect ELDs being set off

Answer 16

insulation testing suspect circuits
operate signals/points to reproduce the fault
waiting for a train to reproduce the fault
inspect for water ingress or defect

Question 17

what must be fitted to the fluke meter when testing

Answer 17

a 100k ohm shunt

Question 18

how do you test bus bars with and without ELDs and how often

Answer 18

by busbar voltage to earth or operation of the test switch. performed every maintenance visit

Question 19

what is classified internal wiring

Answer 19

wiring contained in relay rooms, signal boxes, level crossing huts, walk in enclosures, equipment location and cupboards.

Question 20

how often is internal wiring tested with and without ELDs

Answer 20

without ELDs 4 years for PVC and 2 years for anything else.
with ELDs testing is not required.

Question 21

method of insulation resistance testing for internal circuits

Answer 21

circuit to be disconnected at both ends. tested complete with all relays closed. tested to the same earth of racks or cupboards.

Question 22

which cores are the preference to be tested in a multicore cable

Answer 22

the outer layer of cores

Question 23

how often does non vital wiring require inspection and testing

Answer 23

every maintenance visit if connected to a bus bar.
every 2 years if connected into vital signalling ciruits

Question 24

Minimum insulation reading for signal and train working telephone circuits

Answer 24

500k ohm

Question 25

how often should arrestors be tested and with what

Answer 25

every maintenance visit during and immediately after lighting season if in lighting prone areas.
1 year for other locations.
with an arrestor tester

Question 26

when are track circuit cables exempt from insulation testing

Answer 26

where an earth sheath exits, only testing of the sheath is required.
no feed and relay like track circuits are run in same cable route
only a single relay of like track circuits are run in the same cable route
(when cables run in the same route are not of the same frequency of channel for a feed and relay end or relay end combinations.)

Question 27

do you insulation test axle counters

Answer 27

no it is not required

Question 28

Do you insulation test ATP systems

Answer 28

anything from the LEU out is not tested. only a continuity test is permitted

Question 29

what insulation resistance readings should you get for
1) cables free of apparatus
2) terminated cables
3) local tail cables disconnected at location but connected at trackside apparatus

Answer 29

1) greater than 10 mega ohm
2) between 1-10 mega ohm
3) greater than 2 mega ohm

Question 30

What needs to happen if the result is less than 1 Mega ohm for
1) core
2) sheath

Answer 30

1) all cores or wire group must be tested
2) if all conductors are double switched then 20% shall be tested, if not all the cores are to be tested.

Question 31

what are some immediate actions to rectify a core to earth etc.

Answer 31

changing circuits to non-defective cores, temporary rewiring cable, insulation taping of defective sections.

Question 32

what is the process if an insulation test result is less than 200k ohm

Answer 32

it shall be booked out and disconnected.