“Every installation shall, during erection and on completion before being put into service, be inspected and tested to verify, so far as reasonably practicable, that the requirements of the Regulations have been met.” 610.1
“On completion of the verification, according to Regulations 610.1 to 610.5, a certificate shall be prepared.” 610.6
In plain language, every installation whether an addition, alteration or new shall be inspected and tested to ensure that it is safe and fit for purpose and a certificate, either an Electrical Installation Certificate along with a schedule of items inspected and a schedule of tests performed and results shall be issued as evidence of this.
Inspection
This is only using your senses and not taking any measurements or readings. What you are checking for is that the correct materials are used (BS numbers), and that everything been installed correctly and that it is not damaged. The majority of this inspection process can be completed with very little extra effort during the installation process.
You should check, connections of conductors and equipment. Colours of conductors, routing and sizing of cables, presence of fire barriers. All of the methods of protection, devices for isolation, presence of warning notices and many more – see 611.3
Testing
Let’s whip out the test equipment I have my own trusty old Megger MFT1552. Now, what you are doing is ensuing that you methods of protection (normally Automatic Disconnection of Supply) are going to be effective in protecting the user and the installation.
Make sure that all protective conductors are continuous (main earth, main bonding, supplementary bonding and circuit protective conductors)
Check that any ring socket circuits are a ring and that there are no breaks, crosses or too many unfused spurs etc.
Whilst you are doing this you will also be confirming polarity (single pole switches, fuses etc are on the line conductor, sockets connected correctly L, N, E)
Insulation resistance test is checking to ensure that there are no short circuits and earth faults within an installation. We do this by using 500v DC and the easiest way to picture this is as a pressure tests, we are checking for leaks using electricity at a higher pressure than normal.
Happy with this and all of you test results are satisfactory then it’s time to switch on. First though…
Check the incoming supply is safe
Polarity, Ze and PFC and switch on!
Measure individual circuit Zs values and compare these to 80% of the values in BS7671 Tables 41.2, 41.3, 41.4 as appropriate. This is to ensure that you will meet your maximum disconnection times for fault protection see Table 41.1 or regulations 411.3.2.3, 411.3.2.4 (remember if its a TT supply then the maximum Zs values in T41.5 apply ie 30mA RCD and 1667 ohms apply)
RCDs (used usually as additional protection) will meet their maximum disconnection times of 300mS at 1 x their rating or 40mS at 5 x their rating)
Next have a functional check, do things switch on/off are the two way switches working etc.
And if you are happy with all of your results then complete the paperwork ‘Certificate’
Done, easy!
For this example I’ve chosen a very simple single phase domestic installation with a TN-C-S supply as such there are additional tests that have not been mentioned that you may find in say a 3 phase industrial installation. For more help and advice have a look at BS7671:2008+A3:2015, Guidance Note 3, On-Site Guide or email me.
All of the regulation numbers and Tables are from BS7671:2008+A3:2015 Part 4 and Part 6
Paul Moseley (Tutor/Electrician)
www.the-regs.co.uk