Your questions answered

Both documents allow use of either a separate supply circuit dedicated to the smoke alarms or connection to a regularly used local lighting circuit.

2 - Can I connect fire and intruder alarm systems on the same final circuit via a common spur connection?
No. BS 5839 Part 1 clause 16·2 requires a fire alarm to be connected to the load or supply side of the installation's main isolator by a switch fuse or circuit-breaker that is red and used solely for this purpose. This should be labelled 'Fire alarm do not switch off'.

BS 4737 Section 4·1 clause 4·6·1 requires a mains supply spur to be solely used for connection to an intruder alarm, and BS 4737 Part 1 clause 7·2·1 prohibits connection to the mains supply by a plug and socket outlet.

3 - Why is the steel armouring of certain cables unsuitable for use as circuit protective conductors?
There are situations when the heat rise in the cable armouring, caused by earth fault currents, produces a temperature rise that damages the insulation of the remaining circuit conductors within the cable.

The ECA has produced a listing of potentially inadequate steel wire armoured (swa) cables based on the minimum size from BS 7671 table 54G.

A more precise way of deciding the minimum swa size is by using the adiabatic equation method. Generally, by using this method and, depending upon the protective device and earth fault current, the cross-sectional area of the required cpc will be less than that obtained from table 54G. This method allows the use of more sizes and configurations of cables; all that is needed is a calculated or measured earth fault current value and corresponding disconnection time from the protective device characteristic.

4 - Do I need to record a Zs value for circuits protected by a residual current device (rcd) as well as the trip times?
Yes. Regulation 413-02-16 of BS 7671 requires knowledge of Zs for all circuits.

This does not necessarily mean a loop test has to be carried out on such circuits. The Zs value may be derived from the summation of Ze, R1 and R2.

5 - On a TN system, should a Class 1 outside light that can be touched by a person in contact with the general earth mass be protected by a rcd?
No, providing the measured/ calculated Zs value ensures that the circuit protective device operates within 0·4 s or less (Regulation 471-08-03).

Note: Some regional electricity companies recommend the use of Class 2 fittings for such lighting situations when the supply is protective multiple earth.

6 - Must shower circuits on a TN supply be protected by an rcd?
No, providing the measured/ calculated Zs value ensures that the protective device on the shower circuit operates within 5 s or less.

7 - I have been told that I no longer have to bond a stainless steel sink in a kitchen. Is this true?
Yes, this will normally be the case. To comply with the Wiring Regulations, after main bonding has been carried out to all extraneous conductive parts in a property, the only other requirement for supplementary bonding is in locations such as bathrooms. Unless the sink is within such an area, it will not require supplementary bonding.

8 - I undertake a range of electrical work for a number of different clients. I am aware that I should be providing certification but I am often uncertain as to which certificate to use.
Appropriate electrical installation certificates in accordance with the relevant British Standards should accompany all completed installations.

For general electrical works the relevant standard is BS 7671: 2001 Requirements for electrical installations (IEE Wiring Regulations 16th Edition).

Certification is intended to confirm that the system complies with the designer's requirements and it has been constructed, inspected and tested to ensure that the installation, alteration or addition is in accordance with the British Standard.

This ensures that the work carried out does not endanger the safety of persons and livestock from the effects of electric shock and burns, and property from the effects of fire and heat rising from a defective electrical installation.

It can also be used for compliance with the Electricity at Work Regulations 1989 by demonstrating that the electrical systems have been monitored by regular inspection and testing, and records of the test results have been maintained. All forms of certification must be accompanied by test results suitable for the form used.

Certification and reporting for electrical installations should be provided upon completion of the work in the following format:

• electrical installation certificate – certification of new installations, including alterations and additions. The appropriate schedules of test results and schedule of inspections should accompany the certificate (see note, below);
  
• form of electrical installation certificate (small installations) – generally confined to dwellings or small commercial installations, alterations and additions. It is limited to schemes with a maximum of 18 circuits, where the electrical contracting enterprise has been responsible for the design, construction, inspection and testing (see note, below);
  
• minor electrical installation works certificate – for certification of work that does not include the introduction of new circuits eg the addition of a socket outlet or lighting point to an existing circuit;
  
• a separate certificate should be issued for each existing circuit on which minor works has been carried out. It does not need to be issued where work is to an electrical appliance;
  
• periodic inspection report for an electrical installation – is intended for reporting on the condition of an existing installation; it is not a certificate. The appropriate number of schedules of test results and a schedule of inspections should accompany it. No form of electrical installation certificate should be issued in lieu of a periodic inspection report;
  
• schedule of test results and schedule of inspections – these should accompany the relevant forms of certification or report;
  
• electrical certificates, inspection reports and supporting schedules should only be completed and issued by competent persons who have sufficient knowledge and experience, appropriate to the type and complexity of the installation concerned;
  
• the certification issued should reflect the recommendations contained in the appropriate British Standard.

Note: These certificates should not be issued by ECA members on behalf of a third party that has been responsible for the construction of the installation. Where this is the case a periodic report should be issued.

9 - I am finding difference of opinion with contractors as to installing an emergency light above the outside of a property's exit door. What are the requirements?
BS 5266 Part 1 and BS 5266 Part 7 (also known as BS EN 1838) cover emergency lighting for most buildings. Both documents refer to the positioning of emergency lighting luminaires.

BS EN 1838 Clause 4·1 lists the positions in a building that should be emphasised by the siting of an escape lighting luminaire. Item G of this list states "Outside and near each final exit".

Further reference is made in BS 5266: 1999 Clause 6·8·2, which requires that the area immediately outside a final exit has a luminance not significantly lower than immediately inside the exit under emergency conditions. However, the clause also states that local authority lighting already provided on public thoroughfares may be considered to fulfil this recommendation.

It is clear from the British Standard that unless local authority lighting is available, emergency luminaires are required outside final exits.

10 - I am extending the fire alarm system for a nursing home that has an existing bell system. Can I install electronic sounders or sirens in the additional areas?
No. BS 5839 Part 1: 1988 Clause 9·4·2 states that all sounders within a building should have similar sound characteristics unless high ambient noise levels preclude this. Therefore, the extension to the system must use bells. Alternatively, the existing sounders could be changed to a similar noise to that of any new unit installed. This is to avoid confusion or doubt in the minds of occupants in the event of an alarm activating.