Mr. G Domestic Electrical

Inspection & Testing

The purpose of inspection and testing is to ensure the installation is safe. Initially a walk round and visual inspection is conducted, this can highlight potential issues, such as damaged fittings or accessories and visible wiring.

The consumer unit/fuse box will indicate the age of installation and it may have labels attached that provide more information. You will be asked if you have any paperwork for previous work completed. The visual inspection gives the electrician a first feel for what can be expected during the testing.

To begin testing a circuit, the power to it needs to be switched off and the wiring disconnected from the protective device.

Dead Testing (for each circuit):

Continuity - this is to see that there is a connection from one end of each wire to the other and what the resistance of that wire is. The value is expected to be low, typically under 5 ohms - depending on the cable size and length. Generally this is done on the dead circuit by connecting the live wire to the cpc (circuit protective conductor - the earth wire) with a link, then measuring the resistance from the other end. This gives a resistance value for the live wire and the cpc combined (and also checks Polarity - that the connections are the right way around). This is repeated for the neutral - the results should be the same. Final Ring circuits which are unique to the UK have a special testing procedure, where the 2 circuits are tested first as continuous loops and then connected together as one loop (a figure of 8) to check the continuity. The continuity resistance of the wire is needed to calculate whether the protective device does operate in the current time. The values will be recorded on the test certificate.

Insulation - The copper wires are covered in protective insulation (usually PVC), but this can degrade over time, or be damaged by abrasion, cutting or loose connection. A test meter will try and pass 500 volts (twice the usual voltage) between the conductors and see if it leaks; the leakage is shown as a resistance value in mega Ohms (millions of ohms); the value is expected to be high (the reverse of continuity). In many cases prior to the insulation test, equipment/ lighting is unplugged/disconnected. Neons, USB, LED, electronics (smoke alarms) can be damaged by insulation testing. The insulation resistance of the wire is needed to calculate that the leakage current does not operate a protective device. The values will be recorded on the test certificate.

Live Testing (for each circuit):

Earth Fault Loop Impedance (Loop) - The test equipment measured the previous tests for continuity and insulation using DC voltage. The installation will use AC voltage during operation and there is a difference between the measurements recorded during dead testing. Resistance in AC circuits is called impedance and is measured with the power on using the AC voltage (not the DC of the test equipment). The test equipment will now measure the impedance of the circuit (and the prospective fault current) this is needed to calculate that the protective device does and will operate in the current time. The values will be recorded on the test certificate.

example:

a b32 circuit breaker must operate within 0.4 seconds when 5 times the rated current passes through it (160 A)

Voltage = 230v

Factor for voltage fluctuation 0.95 (voltage = 230 x 0.95) = 218.5

Resistance required to operate = voltage / current = 218.5/160 = 1.36 Ohms

Factor for temperature rise = 0.8

1.36 x 0.8 = 1.1 Ohms (rounded)

The value of the circuit impedance for a b32 circuit breaker must be less than 1.1 Ohms otherwise the circuit breaker will not operate in time. High values of impedance are generally caused by long runs of cable, conductor size and poor connections. Only testing can confirm this value.

RCD testing:

The RCD is tested to confirm that the device operates within the correct time and at the correct value. Typically an RCD must operate within 300ms at a value of 30ma or 40ms at 150ma.

Functional testing:

Checking that everything is connected and working correctly.

In summary the testing is not carried out to see if something works but rather to check that it will stop working (the protective device will operate) in the event of a fault. This is exactly what the DIY installer misses out; they only do the last step; functional test. They will know that it works but cannot confirm what may happen if there is a fault.

Making testing easier. It can save money in time charges if access to accessories and fittings is easier. Furniture moved away from sockets / switches, clear access to the consumer unit. Lamps will be removed, devices can be unplugged (fridge, freezer, washing machine). It is obviously important to make sure this all gets reconnected afterwards.

Third Party Certification (TPC)

Why would you need Third Party Certification?

BS7671 Regulation 134.1.1

Good workmanship by one or more skilled or instructed persons and proper materials shall be used in the erection of the electrical installation. The installation of electrical equipment shall take account of manufacturers' instructions.

BS7671 Regulation 134.2.1

During erection and on completion of an installation or an addition or alteration to an installation, and before it is put into service, appropriate inspection and testing shall be carried out by skilled persons competent to verify that the requirements of this Standard have been met.

Building Regulations Part P

Regulation 3.1

For notifiable electrical work one of the following three procedures must be used to certify that the work complies with the requirements set out in the Building Regulations.

1. Self-certification by a registered competent person
2. Third-party certification by a registered third-party certifier
3. Certification by a building control body

It's important to note that a Third Party Certifier cannot 'sign off' completed work, the rules are very specific:

Prior To The Work

The Third-Party Certifier (TPC) must be informed in advance of any proposed work that they will be employed to certify before it begins. A plan is defined, a schedule for that plan and payment.

Inspection

The work will need to be inspected by the TPC several times – at least on at first and second fix, before undergoing final testing and then certification by the TPC. Certification must be submitted within 21 days of the date of the final inspection via email.

Report

The TPC will need to complete a ‘Third Party Certifier’s Electrical Installation Report’ for review. When approved and within 30 days of the notification being made, a Building Regulations Compliance Certificate will be sent to the customer via post.

Non-Compliance

A non-compliant installation will be notified to the Local Authority Building Control.

If you have any questions about this please send me a message through the contact page.