inspection and testing Flashcards
before working on any electrical system the circuit must be :
electrically ISOLATED. by using suitable locking off devices.
safe isolate procedure.
- identify the isolation point and ask permission to isolate the supply
- isolate the supply , lock off ( retain key ) & label
- select the appropriate voltage tester & check its condition ( leads to GS38)
- check the voltage tester is functioning by testing on a known live supply or by using a proving unit.
- check the circuit is dead using the voltage tester
( L-N , L-E , N-E) – should all be 0 volts - recheck the voltage tester on an a known supply or by using a proving unit
- commence work
sequence of testing
dead testing first -
- continuity of protective conductors
- continuity of ring final circuit conductors
- insulation resistance test
- polarity ( can be done in step 1 )
followed by live testing -
- Polarity
- Earth fault loop impedance ( ze & zs )
- Prospective fault current
- functional testing ( RCD )
continuity of ring final :
3 steps:
step 1 - test end to end of every conductor . this is to find r1 r2 and rn. (L-L then N-N then CPC-CPC)
step 2 - we cross connect Line and Neutral cables in a connector block and then go to every single point on the circuit and test between Line and Neutral.
step 3 - step 2 repeated but between Line and CPC.
insulation resistance test :
this proves to us that the insulation around conductors is in good condition and there is gonna be no issues in terms of short circuit or earth faults.
so to prove no copper conductors are touching each other we send an extorniate amount of test voltage into the installation.
we send a high voltage (500v) DC down our line conductor and neutral OR our line & cpc OR neutral and cpc. to put the conductors under pressure.
minimum insulation resistance is 1 meg Ω
unplug any connected appliances . remove lamps if its a lighting circuit and make sure switches for lights are on the ON position and be aware of any permanently connected equipment e.g washing machines , cookers etc.
if its SELV or PELV Then you test at 250v and minimum insulation resistance is 0.5 Ω
high results better , in new circuits
Polarity : all conductors must be connected to the correct terminals. any other arrangement can be extremely dangerous.
e.g to confirm switches are in the line conductor only and the cables go to where they should do.
same as test method 1 of continuity of protective conductors.
what is the purpose of Initial verification. EVERYTHING IS CHECKED
inspection for a initial verication is visual and we need to unscrew and check everything thats been installed. everything needs to be inspected and list Is on pg 230-231 section 642
when we have installed a new circuit or changing a consumer unit we need to prove that it is safe to put into service.
defects must be repaired before installation is put into service and re inspected and re tested.
Testing follows the inspection and theres a sequence e.g
and electrical installation certificate must be provided to the person ordering the work. if altering an installation ; adding a socket or light, its needed to provide a minor works certificate to the person ordering the work.
- continuity of conductors - continuity of ring final
- insulation resistance
etc
what is the purpose of condition reporting / periodic inspection.
upon completion of periodic inspection an electrical installation condition report is provided.
aswell as schedule of inspection & inspection of results which has a recommended interval until the next inspection.
is to verify that the installation that is already there is safe to REMAIN in service. for an initial verification work has been done and an issue has been issued however when turning up to do a condition report no work has been done.
defects must be stated in the form of
C1- danger present. immediate action required.
C2- potentially dangerous - urgent action needed.
C3 - improvement recommended
Fi - Further investigation required without delay.
Polarity - live test
we need to make sure that our voltage coming in as we expect it. we know between L-N there should be 230 so we test it to prove. same as L-E which should be 230 and N-E there should be 0volts so we test and prove. we use a AVI to do this.
Earth fault loop impedance
Ze + (r1 + r2) = Zs.
we are proving the impedance of the earth fault loop path which is external to the property
Propspective fault current
seeing if the circuit breaker can handle the current ?
Functional testing including rcd
we turn things on and off to see if its working how we expect it to. RCD test aswell by connecting line neutral and earth to rcd and clicking the press button.
what test certificates do we have to fill out
- electrical installation certificate that needs to hav4 a schedule of inspections and schedule of tests.
- minor electrical works certificate
- electrical installation condition report w schedule of inspections & tests.
continuity of protective conductors:
measure resistance of line and line.
then install a link between line and cpc and temporarily connecting whilst the power is off ( to avoid short circuit ) and test is done at end of circuit. one probe to cpc one probe to line conductor. switches should have been turned back on and will give us the resistance of both wires. R1 + R2. testing at every point and value at the end should be the highest value.
