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C&G Unit 2392-101/102 > Testing Procedures > Flashcards

Testing Procedures Flashcards

1
Q

Fill in the blanks

When testing, you will need an instrument(s) cable of measuring the following:
1. ____ (compliant with ____38)
2. ____uity
3. ____ resistance
4. ____ - ____ loop ____ [__ __ L]
5. Prospective ____ - ____ current [P____C]
6. Prospective ____ current [P ____ C]
7. ____ function

A
  1. Voltage, GS
  2. Continuity
  3. Insulation
  4. Earth-fault loop impedance, EFL
  5. short-circuit, PSC
  6. fault, PFC
  7. RCD
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2
Q

When testing for CPC Continuity…

In Continuity Test Method 1:
Which conductor is used as the return path for the test current?

A

The line conductor

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3
Q

In Continuity Test Method 1:

There are three steps to measuring the CPC, what are they?

A
  1. Link the earth and line conductor at the CCU (best practice is to remove them from their terminals and connect them together using a connector block)
  2. Measure the accessory at the furthest point of the circuit. Record this reading. This will give you your [R1+R2] value.
  3. Repeat the steps above, but with the Line and Neutral conductors, this will give you your [R1+Rn] value.
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4
Q

What additional piece of kit is needed when using testing method 2 of CPC continuity & main bonding conductors?

A

A ‘wandering lead’

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5
Q

True or false:
Testing method 2 is the recommended method for continuity & bonding testing

A

True.

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6
Q

What must be done to the testing machine before commencing testing?

A

The leads must be nulled, if they cannot be nulled, the resistance of the leads themselves must be taken away from the final results.

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7
Q

Why is ring final circuit testing so crucial?

A

It is crucial because if there is a break in the continuity of the circuit, it inadvertantly creates two radial circuits which have inadequate rating protection. If they are under full load, the protective device will not operate properly, possibly causing a fire.

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8
Q

When using testing a final ring circuit, what must be taken out of the Consumer Unit?

A

Both ends of the loop forming the final ring circuit.

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9
Q

When testing a final ring circuit…

Once the ends of the loop are taken out of the consumer unit, what comes next?

A

Their resistances must be measured and recorded

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10
Q

During the first step of testing a final ring circuit…

  1. Roughly, how close together should the resistances of the line and neutral conductor be in terms of resistance values?
  2. Will the resistance of the CPC be higher or lower?
  3. Why is this?
  4. If any readings are suspect, what should be checked?
A
  1. Roughly, they should be within 0.05Ω of each other.
  2. The CPC will have a higher resistance.
  3. This is because of the lower CSA of the CPC.
  4. The tightness of the connections at all points in the circuit should be checked.
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11
Q

When testing a final ring circuit…

In step 2, which two conductors are connected together in a ‘figure of 8’?

A

The line and neutral conductors, inside a connector block

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12
Q

When testing a final ring circuit…

  1. In step 2, where are the test probes located?
  2. What kind of reading are you expecting?
A
  1. The resistance between line and neutral at each socket
  2. The resistances to be roughly the same at each socket, and these values to be roughly one quarter of the reading obtained from the line and neutral loop.
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13
Q

When testing a final ring circuit…

Which two conductors are connected together at the CCU in step 3?

A

The line and the CPC.

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14
Q

When testing a final ring cirtcuit…

True or false:
The results in step 3 should be similar in nature to those performed in step 2.

A

True.
The testing procedure is the same, the resistance value of the full loop should be approximately 4 times the value of each individual socket reading.

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15
Q

When testing a final ring circuit…

  1. What reading is given to the name of the highest reading in step 3?
  2. What can this be used for?
  3. Where must it be recorded?
A
  1. R1 + R2
  2. R1 + R2 is used when calculating the Earth Fault Loop Impedance of the circuit (Zs).
  3. It must be recorded in the Schedule of Test Results.
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16
Q

Once final ring circuit continuity has been established, what does this also confirm?

A

Correct polarity of the circuit, further testing for this is unnessecary.

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17
Q

When performing continuity tests…

True or false:
Any kind of testing equipment can be used to establish the continuity of a circuit.

Bonus:
What must never be used for a continuity test?

A

False.
You must always use a low-resistance ohmmeter for continuity tests.

You should never use an insulation resistance tester, as this can provide false continuity.

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18
Q

What is the purpose of carrying out an insulation resistance test?

A

An insulation resistance test verifies the basic protection of each of the conductors by verifying the condition of the insulation surrounding each of the conductors in any given circuit.

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19
Q

What voltages (and what type) can be delivered using an insulation resistance tester?

A
  • 250V DC for SELV and PELV circuits
  • 500V DC for circuits rated up to 500V
  • 1000V DC for circuits between 500V & 1000V
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20
Q

When carrying out an insulation resistance test…

What must be done to ensure accurate readings?

11 things which is exhaustive, but important

A

The following must be done to the entire system:
1. Main switch turned off
2. Circuit breakers must be turned off and fuses stored in your pocket
3. All Appliances must be turned off.
4. Outlets supplying sensitive electronic equipment such as doorbells, fire alarms, burglar alarms etc. must be disconnected
5. All lamps must be removed
6. Flourescent luminaires must be disconnected
7. Passive infrared sensors must be removed
8. Neon indicators must be removed or L&N conductors linked together and then to the CPC.
9. Dimmer switches must be disconnected and their conductors linked together in a terminal block
10. One way lighting must be in the on posistion.
11. Two Way Switching & Two Way & intermediate switches must all be operated to ensure that all conductors are tested.

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21
Q

When performing an insulation resistance test…

True or false:
The testing order is:
1. Line - Neutral Terminal
2. Earth Bar - Neutral Terminal & then Live terminal

A

True.
This is the correct order to do things.

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22
Q

When performing an insulation resistance test:

What are the expected test results for the following circuit types:
1. SELV & PELV
2. Up to 500V & FELV circuits
3. 500V+ circuits

What is the more likely reading you will recieve in this instance?

A
  1. 0.5 MΩ
  2. 1.0 MΩ
  3. 1.0 MΩ

100+ MΩ is the more likely reading you will recieve.

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23
Q

When performing an insulation resistance test…

Below what reading should you investigate further?
How would you go about investigating further?

A
  • Below 2 MΩ
  • By testing each circuit individually to determine where the issue is.
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24
Q

Why are insulation resistance tests carried out with such high voltages?

A

This is because if the insulation doesn’t degrade under very high voltages, it should not degrade at a lower voltage.

25
Q

What are the three main goals of a polarity test?
What does a successful polarity test provide?

A
  1. That all single-pole protection devices (fuses, breakers) and switching devices are connected in the line conductor only.
  2. That all sockets are connected with the live connection on the right-hand side. And prevents an appliance’s lead remaining live when turned off.
  3. The line conductor is in the centre pin of any edison screw lamp holders, which prevents the surrounding metalwork from becoming live.

A succcessful polarity test reduces the risk of shock and damage to equipment.

26
Q

What testing device is used to carry out a polarity test?

A

A low-reading ohmmeter.

27
Q

Explain the process of performing a polarity test step by step, leaving out the expected results and what they mean.

A

Step 1: Safe isolation
Step 2: Remove bulb & cover from CCU
Step 3: Connect the line and earth conductors of the lighting circuit in the CCU
Step 4: Using the meter probes, touch the line and earth terminals at each lighting point.
Step 5: Operate the switch/switches controlling the lighting point(s) to confirm polarity.

28
Q

What results can be gained from a polarity test and what do they mean?

A

There are two possible results.

29
Q

Why is continuity testing so vital?
Particularly with CPCs?

A

Conductors must be electrically continuous throughout their length with no breaks (open circuit), high resistance (loose or corroded connection) or excessive resistance (cables too long).

Continuity of CPCs is very important, because this will ensure the appropriate disconnection time for the installation in the event of a fault.

30
Q

If test leads cannot be zero’d, what must be done to ensure accurate readings?

A

The resistance of the leads themselves must be established, and this value subtracted from the resistance measured.

31
Q

Why must the earth path be continuous?

A

If the earth path is not continuous (including bonding of extraneous or exposed metal parts), it could lead to one of these parts becoming live during the event of an earth fault, which could result in a direct contact shock.

32
Q

True or false:
You don’t need to confirm the continuity of the line and neutral conductors when testing a CPC.

A

False.
All parts of the circuit must be electrically continuous, as they ensure the circuit is working properly.

33
Q

When testing a final ring circuit…

True or false:
Your testing device needs to be able to be capable of distinguishing differing values as little as 0.05Ω

A

True.
The reason for this is to allow for any resistance in the test leads.

34
Q

Illustrate the four steps in the first part of performing a final ring circuit continuity test.

A
  1. Securely isolate (all steps) the entire circuit/ installation
  2. Identify and disconnect the line, neutral and cpc of the final ring circuit being tested (two of each).
  3. Measure the resistance of all conductors disconnected, the entire loop.
  4. Record measurements.
35
Q

After performing the initial step of final ring continuity…

What three values will you be given?
What do these values correlate to?

A

End to end Live conductor resistance - R1
End to end Neutral conductor resistance - Rn
End to end CPC resistance - R2

36
Q

After recording the values given in Step one of final ring circuit continuity, which of the three values will be the highest?
Why is this?

A

The R2 value (end to end resistance of the CPC) will be the highest.
This is due to the lower CSA of the CPC*

  • If the installation is made using twin & earth cable, as the CPC will be 1.5mm.
37
Q

What is the mathmatical relationship between the value fo the end-to-end resistances of the final ring circuit conductors and the individual sockets?

What could be the issue if these relationships are not present?

When measuring the line and neutral conductors of the ring.

A
  1. The individual socket readings should be half of the end-to-end readings.
  2. The conductors have been incorrectly identified, or there is a break in continuity in the ring.
38
Q

When performing a final ring circuit continuity test…

Illustrate the three steps that make up step 2 of the process.

A
  1. Connect the outgoing line conductor to the incoming neutral conductor and vice versa, using a crocodile clip from the tester, so that they are cross-connected in a figure of eight arrangement.
  2. Measure the resistance of this figure of eight, and record the result. This should be approximately half of the end-to-end readings for the line or neutral condctors (R1 + Rn) / 4.
  3. Remove the crocodile clips and connect the line and neutral conductors using a connector block to maintain the connection. Go to each individual socket, and test the line and neutral terminals. This result should be the same as the one acquired at the consumer unit.
39
Q

When performing a final ring circuit continuity test…

Illustrate the three steps that make up step 3 of the process.

A
  1. Connect the outgoing line conductor to the incoming circuit protective conductor and vice versa, using a crocodile clip from the tester, so that they are cross-connected in a figure of eight arrangement.
  2. Measure the resistance of this figure of eight, and record the result. This will be higher due to the lower CSA of the CPC. Record the result from each socket.
  3. Use the highest recorded resistance of this test for the R1 + R2 value, which is used to calculate the Zs (loop impedance) of the circuit.
40
Q

True or false:
When testing a final ring circuit’s continuity, any spurs off the main ring will have a lower resistance when performing step 3 (cross connection of CPC and line conductor).

A

False.
Any spurs of the ring circuit will have a higher resistance value. If this is the highest resistance value recorded, it should be used as the R1+R2 value for the circuit.

41
Q

True or false:
If all three steps of testing the continuity of a final ring circuit are performed correctly, it also confirms the correct polarity of the circuit.

A

True.
If the polarity was incorrect (wrong conductors in place) then the readings would be wrong, therefore continuity is confirmed.

42
Q

What is the final step of testing a final ring circuit’s continuity?

A

Reconnecting the previously disconnected conductors.

43
Q

When performing an insulation resistance test…

All equipment ____ to testing must be disconnected or circumvented.

A

vulnerable

44
Q

When performing an insulation resistance test…

What two kinds of electrical items must be disconnected?

A
  • Equipment (dimmer switches, delay timers, RCDs etc.)
  • Loads (lamps, motors, appliances)
45
Q

When performing an insulation resistance test…

True or false:
Equipment which cannot be disconnected (due to impracticality or inaccesibility) may have their line and neutral conductors temporaryily linked together.

A

True.
Where the test voltage would damage equipment, this should be performed. As well as linking together live conductors and earthing arrangements.

46
Q

What is the current that an Insulation Resistance test should be performed at?

A

1mA (1 milliamp)

47
Q

Illustrate the six steps of performing the first part of an insulation resistance test.

A
  1. Securely isolate the installation/ circuit to be tested from the supply, including the neutral.
  2. Disconnect all current using equipment from the circuit, remove all lamps and check that all switches are closed. If there is equipment connected which would be sensitive to the test voltage, it is imperative that local switching is used to protect the equipment.
  3. Check that the instrument and leads are in sound condition.
  4. Check the condition of the testing device’s batteries.
  5. Select the appropriate test voltage and range.
  6. Connect the instrument, and record the Line to Neutral reading.
48
Q

When performing an insulation resistance test…

True or false:
If there is equipment which is not vulnerable to the test voltage, you can test the equipment in any order you wish.

A

False.
You must test the line and neutral seperately to earth:
* Line to earth.
* Neutral to earth.

49
Q

When performing an insulation resistance test…

True or false:
Where there is equipment which is not practical to disconnect, you must connect the line and neutral conductors together and test between them.

A

True.
This ensures that all of the installation is checked.

50
Q

True or false:
A Zₑ test can only be measured at the origin of the installation.

A

True.
This is because you are measuring the external part of the earth fault loop.

51
Q

When ascertaining the Zₑ value of an installation…

True or false:
You do not need to remove the earthing conductor (external) from the main earthing terminal in the CCU.

A

False.
You need to remove this conductor, as the purpose of the test is to determine if the intended path for the earth fault current is suitable.

52
Q

True or false:
Zₑ is required for all circuits that form an installation.

A

False.
This is only required from the main entry point, the live terminal on the main switch. Otherwise it would be difficult to choose one value to use.

53
Q

True or false:
An earth fault loop impedance test (Ze) can be done live.

A

False.
It must be done whilst the installation is de-energized otherwise the disconnection of the main earthing conductor would constitute a serious health risk, as the installation is disconnected from one of its main safety features.

54
Q

True or false:
Zs tests must be done live.

A

True.
These tests can be done live because they do not require earthing to be disconnected.

55
Q

True or false:
You must gain a Zs reading from each circuit of the system.

A

True.
You would test the furthest point of the system from the consumer unit or distribution board. Known as ‘the end of the line’.

56
Q

How do you go about testing for Zs?

4 Steps

A
  • Select the appropriate point on the circuit
  • Use the plug extension
  • Set the tester to Zs mode
  • Record the results
57
Q

What are the two steps required in functional testing?

A
  • Using an RCD testing device
  • Using the ‘Test’ button on the RCD itself
58
Q

True or false:
An RCD test should use both sides of the AC cycle.

A

True.
Tests need to take place at both 0 degrees and 180 degress of the AC cycle.

C&G Unit 2392-101/102 (12 decks)

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