Week 12 Flashcards
(20 cards)
The testing of an installation implies
The use of instruments to obtain readings
Why is visual tests important
And when it just be done
What is the aim of visual inspection
To identify cracked socket outlets, chipped or loose switch plate, or a missing conduit-box lid or saddle
The installation must be visually inspected before testing begins
The aim is to confirm that all equipment and accessories are undamaged and comply with IEC standards
Visual inspection checklist (12)
- Electrical intake equipment
- Parallel or switched alternative sources of supply
- Automatic disconnection of the supply
- Other methods of protection
- Basic protection
- Fault protection
- Additional protection like RCD and bonding
8.specific inspection examples as appropriate to the installation: - Distribution equipment
- Circuits
- Isolation and switching
- Current using equipments (permanently connected)
Why tests must be carried out in the sequence given in EC
For reasons of safety and accuracy
Testing before the supply connected
- Test for continuity of protective conductors including bounding
- Test for continuity of all ring final circuit conductors
- Test of insulation resistance
- Test for polarity using the continuity method
- Test the earth electrode resistance
With the supply connected (4)
- Re-check polarity using voltemeter or test lamp
- Test of earth loop impedance
- Check phase sequence
- Functional test, additional protection testing
To measure accurately the resistance of the conductors, what must be done?
Use an instrument capable of producing an open circuit voltage of between 4 and 24 V AC or DC, and delivering a short Circuit current not less than 200mA
Continuity testing and insulation resistance resting are combined in one instrument.
For insulation resistance tester
The test instrument must be capable of detecting insulation leakage between live conductors and earth
The test instrument must be capable of producing a test voltage of 250,500 or 100V and delivering output current of 1mA
Earth fault loop impedance tester
The test instrument must be capable of delivering fault currents as as high 25A up to 40 mS using supply voltage, during the testthe instrument does ohms law calculation and displays the test result as a resistance reading
RCD tester
To ensure RCD will operate very quickly under fault conditions and within the time limits
The instrument must simulate a fault and measure the time taken for the RCD to operate
The instrument gives a reading measured in milliseconds to in-service accuracy of 10%
The object of continuity of protective conductors including main and supplementary equipotential bonding tests
To ensure that the circuit protective conductor CPC is correctly connected
Electrically sound
Has a total resistance which is low enough to permit the over current protective device to operate within the disconnection time should an earth fault occur
For testing continuity protective conductors, which conductors should be tested
Every protective conductor must be separately tested from the consumers main protective earthing terminal, including the main protective bonding and supplementary protective bonding conductors
Testing for continuity of ring final circuit conductors
Objects
How
The object is to ensure all ring circuit cables are confines around the ring, there is no break and no interconnection, and all connections are electrically and mechanically sound, also verify polarity of each socket outlet.
The test is made with the supply disconnected using an ohmmeter.
Disconnect and separate the conductorS of both legs of the ring at the main fuse
First step of testing continuity of ring final circuit conductors
Measure the resistance of the line conductors (L1&L2), neutral conductors( N1&N2), and protective conductors(E1&E2) at the main positions
End to end live and neutral conductors should be- approximately the same if the ring is continuous I
If 2.511.5 mm cable is used, PE will be 1.67 times these reading
Second step of test of continuity of sing final circuit conductors
Live and neutral conductors should be temporarily joined together.
Ohmmeter reading is taken between the live and neutral at every socket out Len on the ring circuit,the readings should be the same to indicate there is no breaks or multiple loops in the ring.
Each reading approximately = 1/2 the live and neutral reading in step 1
Third step of testing continuity of ring final circuit conductors
CDC wired as a ring, temporarily join the live and CPC to gather, and un ohmmeter reading should be taken between live and earth in every socket outlet on the ring
The readings should be the same to indicate. That there is no breaks or multiple loops in the ring
The blue should be R1+R2 for the circuit
Step 3 R1 +R2 = step 1 (r1+r2)/4
Testing insulation resistance
Objectives
Where should be made?
Instrument
To verify the quality of the insulation is satisfactory and has not deteriorated or short circuited
The test should be made at the costumers unit with the main switched off,all fuses in place, all switches closed
There are two tests to be carried using insulation resistance tester, it must have a test voltage of 500 dc for 230 and 400v installations
Procedures for insulation resistance test for:
Line and neutral conductors to earth:
1. Remove all lamps
2. Close all switches and circuit breakers
3. Disconnect appliances
4. Test separately between the line conductors and earth, and between neutral conductors and earth for every distribution circuit at costumers unit and record results in table
Between line conductors:
1. Remove all lamps
2. Close all switches and circuit breakers
3. Disconnect appliances
4. Test between line and neutral conductors of every distribution circuit at the casters unit and record the results
Polarity test
Objectives and procedure
To verify all fuses, circuit breakers and switches are connected in the line or live conductors only, all socket outlets correctly wired
The test is done with the supply disconnected using ohmmeter or continent y tester
1. Switch off the supply at the main switch
2. Remove all lamps and appliances
3. Fix a temporary link between the line and earth connections on the consumer side of the main switch
4. Test between common and earth at each switch
5, test between center pin of any Edison screw lamp holders and earth
6. Test between live pin (at right) and earth at each socket outlet..
Functional testing
To ensure that the accessories and equipment do what they are supposed to do within the installation, it’s a hands-on test
Examples:
* do switch toggles operate as they are supposed to operate?
* do the electrical isolators switch on and off as they are suppose to do? Is the device fixed and secured?
* does the test button on any installed RCD effectively operate the device?
