Periodic Inspection and Testing
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Periodic inspection and testing at regular intervals is a requirement of BS7671. Inspection consists of a visual inspection of the installation to ensure that the installation complies with the current building regulations and is up to the standard required by BS 7671. Inspection also identifies any damage or deterioration that may have occurred though use or overloading.
Electricial testing involves the use of test meters to determine the continuity and insulation of conductors, polarity and to ensure that disconnection times are met. The person conducting the assessment will then issue a certificate, a legal document that states whether the installation is satisfactory or if work is required to bring it up to the current standard.
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Initial verification |
Exposing the fuse carriers |
Country and Town Maintenance, CTM, electricians are qualified to undertake these electrical safety checks. This step-by-step guide will give you an insight into what is involved in a periodic inspection and test. The guide is divided into four main parts. These are inspection, the faults picked up during the inspection, testing and report writing.
Electrical Inspection: Initial verification
All electrical installations deteriorate with time and need regular electrical safety checks. The initial verification part of the periodic inspection and test enables the electrician to get a feel for the location, the type of use or misuse of the installation, the maintenance it has received and the conditions to which it is subjected. In broad terms areas of compliance and no-compliance with current regulations are noted.
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Checking the size of the suppliers fuse for earthing arrangements |
Inspecting the earthing arrangements |
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10mm Main bond to water |
Checking the conductors under the fuse carriers |
Electrical Inspection: Checking accessories
Visually checking the wiring behind and inside accessories can show signs of wear or overloading. It would also show poor workmanship and departures from the regulations if these exist. The work carried out for a periodic report does not require the electrician to open all accessories but a sample of each kind from each circuit. This is because the process of dismantling and reassembly may cause damage to cables. However if problems exist in the sample then further investigation in all accessories may be required.
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Investigating behind accessories |
Checking the condition of conductors behind accessory |
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Checking supplementary bonding |
Noting the quality of the installation |
Electrical Faults
During a periodic inspection it is common to discover faults with the installation; just a few photos are shown here. If you would like to see more examples, visit the fault section of the gallery.
When faults are uncovered they are noted on the periodic report and given a classification of 1 – 4;
• Code 1 Requires urgent attention e.g. danger exists
• Code 2 Requires improvement e.g. potential danger
• Code 3 Requires further investigation
e.g. item is outside intended purpose or limitation but the inspector was unable to come to a conclusion
• Code 4 Does not comply with BS7671
e.g. outside of the most up to date regulations but users are not at danger as a result.
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Line conductor incorrectly marked as CPC |
Live conductor taped to heating flow pipe |
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Exposed conductive parts |
Fitting not suitable for zone |
Electrical Testing: Dead tests
Once the electrical inspection part of the periodic has been completed the inspector will move on to the electrical testing. The inspector will probably spend 70% of his time on inspection and 30% on testing. The electrical tests must be completed in a strict order and dead tests must be completed satisfactorily before the live test commence.
The dead tests are:
• Continuity of protective conductors including main and supplementary bonding
• Continuity of ring final circuit conductors
• Insulation resistance
• Protection by separation of circuits
• Polarity
• Earth electrode resistance
The photos show images of r1 and R1+ R2 tests. Using a low resistance ohmmeter the resistance of the conductors is established and checked against limiting values for cable, circuit type and protective device. R1 is the name given to the ‘line’ conductor this is the live brown conductor. R2 is the CPC or earth. Rn not shown here is the blue neutral conductor. r1, r2 and rn are the same conductors as above but form part of a final ring circuit.
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First stage of final ring test taking |
Last stage of final ring test taking R1 + R2 readings |
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Preparing to take a R1 + R2 reading |
Taking an R1 + R2 reading notice earth bar connection |
Electrical Testing: Live tests
The live electrical tests follow on from the dead test. With suitable results the periodic inspector knows that it is safe for him to continue working on a live installation.
Live tests are classified as follows:
• Protection by automatic disconnection of supply
• Earth fault loop impedance
• Operation of residual current devices
• Prospective fault current
• Functional testing
• Voltage drop
Here the photos show Ze and Zs tests being made. A Ze test checks the loop impedance outside of the property. A Zs test checks the total loop impedance from the end point on the circuit along the protective conductor or earth out to the suppliers means of earthing or through the earth electrode, through the earthed neutral point of the transformer, the transformer winding and back along the line conductor, through the consumer unit and back to the accessory.
The R1 and R2 tests are importance as Zs = Ze + (R1 + R2) with Ze, the external loop impedance, being kept at a prescribed limit by the electrical distributor. In general terms the lower the Zs in ohms the better, as according to Ohm’s law V=IR which could be rewritten as I=V/R where V = voltage in volts (V), I = current in amps (A) and R = resistance in ohms (Ω), the lower the resistance the greater the fault current. Larger fault currents operate protective devices quicker thereby removing fault currents before they present a danger to users.
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Conducting a Ze test |
Checking loop impedance on final ring Zs |
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Taking a Zs reading using an adaptor |
Taking a Zs reading using an adaptor |
Report writing
The reporting part of the periodic inspection and test will be completed off site. The inspector will transfer all the information gathered on to a printed report in a format acceptable to the Secretary of State. This is usually four pages but can be longer in larger properties where additional pages are added to include large numbers of circuits or observations. This will then be handed to the person ordering the work.
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Recording observations and test results |
Report a four page document to be completed at the office |
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