ELECSA talks through the options available to installers for connecting appliances to the fixed wiring of an installation.
There are several options available for connecting appliances to the fixed wiring of an installation which can provide a means of local isolation and/or switching off for mechanical maintenance.
These may include the use of a double-pole switch (DPS) or a fused connection unit (FCU).
N.B. The use of a plug and a socket-outlet is not discussed in this article.
Typically, in a new installation, all relevant inspection and testing prior to the connection of equipment should have been carried out.
However, before the connection of any Class I appliance is made to the fixed wiring in an existing installation, the installer should verify that a suitable means of earthing is available at the point at which the connection to the fixed wiring is to be made.
Failure to meet this requirement may lead to exposed-conductive-parts having a raised potential under fault conditions, creating a risk of electric shock.
Furthermore, failure to identify the correct polarity of the fixed wiring at the point of connection, as required in Regulation 643.6, may create a potential shock risk.
Such a situation may exist in an installation where, for example; a single pole protective device may have been inadvertently installed in the neutral rather than the line conductor.
Likewise, incorrect polarity may damage equipment and/or lead to unwanted tripping of RCD/RCBO protective devices.
Connection of appliances
Care should be taken when selecting the suitability and type of cable to be used for a particular application.
BS 7671 permits the use of a T & E type cable for the connection of equipment such as an oven, cooker and/or electric hob.
However, where the operating temperature of the equipment is likely to exceed 70°C, thereby creating a potential risk of thermal damage to the conductor installation, additional protection may be required (Regulation 522.2.201). Such methods of protection may include the use of a heat resistant flexible cable.
The requirements of BS EN 60335-1 for Household and similar electrical appliances – Safety, provides guidance and recommendations on the minimum conductor size of the fixed wiring in relation to the current rating and flexible cord size of the appliance.
In addition, where the connection of an appliance is to be made using a flexible cable, the maximum recommended length in relation to the current rating of the appliance as referred in Table 11 BS EN 60335-1 Household and Similar electrical appliances – Safety, should not be exceeded.
However, where there is any doubt in selecting an appropriate size cable relating to the installed length, a calculation for maximum voltage drop will need to be carried out.
Testing and verification
Where items of equipment having exposed-conductive-parts are connected in circuit, such as electric cookers, washing machines and fridge freezers, Regulation 643.2.1 requires the continuity of protective conductors to be verified by measurement of resistance.
The preferred method for verifying the adequacy of the earth at the connection point would be for installer to perform an earth continuity test.
This can be achieved by one of the following methods:
- temporarily connecting together the line and associated circuit protective conductor at the consumer unit, then verify the value of resistance of line and protective conductor (R1+R2) at the accessory, or
- use a wander test lead (R2 method), a connection should be made between the main earthing terminal (MET) and the earth point of the outlet and likewise on the metal casing of the appliance.
Suitable test instruments such as a low-resistance ohmmeter or a multi-function instrument set to its continuity range should be used for carrying out this test.
In addition, where the (R1+R2) continuity test is performed, this also confirms the verification of polarity as required by Regulation 643.6.
Typically, within domestic premises, the requirements for additional protection are likely to be met by an RCD having a rated residual current not exceeding 30 mA.
Where an appliance is connected to a circuit having RCD protection, Regulation 643.8 requires its effectiveness to be verified by visual inspection and testing for compliance with the requirements of Chapter 41.
This should be checked for operation using an appropriate test instrument, preferably carried out at the terminals of the device. The test button on the RCD should also be pressed to verify its operation.
Information on RCDs (including testing) is given in the NICEIC and ELECSA publication, Domestic Periodic Inspection Testing and Reporting.
There is no requirement in BS 7671 for a Minor Works or an Electrical Installation certificate to be produced when connecting appliances via an FCU or DPS.
As such, no additions or alterations have been made to the fixed wiring of the installation.
However, it would be beneficial to both the contractor and client if records of the work carried out are kept, and it should include the values of resistance of continuity of conductors and the RCD operating times.
Such results may be necessary for future reference and provide an audit trail.
The contractor’s original works order or copies of the receipt issued for payment are useful documents to record information.
For non-domestic premises such as rented accommodation, offices and the like, all appliances whether installed via an FCU, DPS or a plug and socket-outlet, would need to be added to an equipment register as part of the management of In-Service Inspection and Testing of Electrical Equipment (ISITEE).
However, the In-Service Inspection and Testing regime for connected items of equipment may vary between different organisations.
Some organisations may consider the equipment as a portable appliance requiring an annual test, whilst others may include connected equipment as part of the fixed wiring of the installation and is inspected less frequently.
There is no requirement to carry out any physical testing of new appliances. A visual inspection to verify that no damage was incurred during transit and a functional test after the installation was completed would generally be sufficient.
However, an additional check on the continuity of the protective conductor between the connection point and the casing of the Class I equipment would be considered reasonable.
Where an appliance is pre-used, it may be prudent to carry out a formal visual inspection and test to verify that the appliance is safe to be put into service.
Appliances which have previously been used are likely to have missing components such as screws, cable cord grips and the like.
Cable terminations within the equipment often have stripped threads leading to loose connections which may become a potential fire risk.
Any equipment found to be damaged or faulty during an inspection should not be put into service.
Before connecting appliances to the fixed wiring of an existing installation via an FCU or DPS, the installer should verify the integrity of the fixed wiring through an earth continuity and polarity check.
Whilst there is no requirement to provide the client with a certificate, there should be some form of documented evidence outlining the work carried out.
The name and address of the contractor and the date, along with the instrument readings taken (where applicable) should be recorded for future reference.
Where the premises are non-domestic, any paperwork associated with the appliances such as guarantees should be passed to the duty holder who is responsible for the ISITEE.
This would allow for the equipment register to be updated with the newly installed appliances.
For more of ELECSA’s technical advice click here.