In most new building developments the fused connection unit (the spur) for the control and indicating equipment has been supplied by a qualified electrician.
Therefore, in these applications the security installer has had no active part to play in the installation of the mains supply.
Historically, all those involved with security networks have been regarded as more specialist when installing extra low voltage (ELV) wiring, as the vast majority of their system components have not been cabled to work at 230V ac mains potential.
The voltage band of ELV wiring has never been governed by regulations in the same way as mains wiring (known as the low voltage supply) as the latter must be installed and protected against mec-hanical damage, the effects of the environment and electrical overcurrents.
In addition, mains cabling must be run so that people and livestock are protected in total from all the dangers that such an electrical installation may create. However, with the impending addition of electrical safety to the Building Regulations (Part P), new controls on electrical work will become enshrined in law.
The security installer will, therefore, have to demonstrate competence by having attended and been assessed within a recognised Electrotechnical Assessment Scheme or an equivalent course.
Increasing danger hazards
All those involved at any installation level with mains voltage cabling must now realise the implications of the theoretical and practical technical content that this actively involves.
Security installers are committed to make this move in any event for obvious safety reasons.
We also need to be able to react to a greater use of integrated systems with mains derived power supplies plus the linking of traditional security techniques with mains potential lighting, management and automation networks.
All these present increasing danger hazards unless the workforce is capable of installing them correctly.
It is a requirement that all of the work on the mains supply must be carried out by a competent person and the final inspection and testing of the circuit must be performed with a certificate of compliance issued to the customer by the inspector in accordance with BS 7671.
If he is not qualified, the electrical installation needs to be subcontracted out .. or the installer runs the risk of prosecution.
BS7671 has long been the base document used in the electrical contracting industry and originally referred to as the wiring regulations.
Produced as a BS following a consensus of opinion between the Institute of Electrical Engineers (IEE) and the British Standards Institution (BSI) it now appears as BS 7671:2001.
It covers all of the electrical work in which the security installer has an involvement but does not extend to vehicles, ships and lifts.
The implications
Security installers must now increasingly look at a means of being able to demonstrate competence by gaining the knowledge and proving an ability to work safely within the industry guidelines and regulations for their work activities.
Installers must be alert to the following implications:
- The dangers of electricity and the implications of legislation
- BS 7671, The Electricity at Work Regulations and the terms of the Health and Safety at Work Act
- Precautions and means of protection against electric shock and the basics of first aid
- The electricity supply: Single and three phase supplies
- Frequency and current
- Ring final circuits, radial circuits and protective conductors
- Cabling and protection techniques
- Circuit isolation and 'lock off' procedures
- Circuit breakers; Polarity; Earth fault loop impedance
- Installing fused connection units (spurs) Connections within junction boxes and control and indicating equipment
- Inspection and testing of the installation
- Official documentation and reports
- Health and Safety considerations
What are the tests?
Although the security installer may be involved with only a small portion of any electrical installa-tion (since the circuits are ultimately derived from the main distribution board) they do have an effect on the overall wiring system so can interfere with, or compromise, the safety of other circuits.
However, as the security installer does not accept responsibility for the complete electrical installation, the tests can be limited to:
- An initial visual inspection
- Continuity of the protective conductor
- Insulation resistance
- Polarity
- Earth fault loop impedance
- A final visual inspection
- Recording of the information
Visual inspections
These are to detail the actual installation of the supply together with checks to prove that the equipment is of the correct type, size and rating, ie when installing a circuit with a fused spur it is necessary to detail the cable type, wiring route and include information on the siting of the spur in relation to the equipment it supplies, together with the size of fuse installed etc
An inspection of the mechanical supports and protection of the cables and housings must be carried out and detailed. The final inspection will be carried out prior to the recording of information details on the official security company forms.
Continuity of the protective conductor
The continuity of the earth protective conductor test is performed with a continuity tester. There is also a need to prove the continuity of the phase, neutral and protective conductors on final ring circuits to ensure that there is no interconnecting of multiple loops.
Insulation resistance
An insulation resistance test must always be per-formed before any permanent connection to the supply is made. In relative terms, the measure-ment should be very high in the order of many millions of ohms. The reading is to be taken p.33 between the phase and earth. The insulation should be stressed to twice the supply voltage but need not exceed a potential of 500v dc. The insulation resistance should not be less than 0.5W as the minimum acceptable value.
The test requires an insulation resistance tester as it cannot be performed correctly with a multimeter. These instruments are unable to achieve the required voltage.
Polarity test
This is needed to ensure that the phase and neutral are not reversed as all fuses and single pole devices such as MCBs must be connected in the phase conductor only.
The test can be done in various ways using proprietary test equipment.
It is also necessary to prove that the protective conductor (earth) and neutral have not been reversed.
Earth fault loop impedance
This test is required to take into account the result of an earth fault in a piece of equipment. The path that would be followed by the fault current is called the earth fault loop.
The speed at which a protective device will disconnect a circuit is dependent upon the size of the fault current, which is, in turn, dependent upon the value of the phase to earth fault loop impedance (Zs).
BS 7671 contains tables of the maximum values of earth fault loop impedance (Zs) in order to minimise the time that any metalwork within the electrical installation will remain live.
The actual test is carried out with a live system by generating a small level of current down the circuit protective conductor to simulate a fault and then calculating the corresponding impedance.
It must be appreciated that when this is occurring, any metalwork within the installation will rise in potential.
Testing routines must take account of the hazards and dangers and be arranged to prevent them. Prominent notices should be displayed while testing is in progress.
Earthing fundamentals
There is a need to understand the fundamentals of the earthing requirements because the safety of the entire electrical system relies on the efficiency of the building earth protective conductor.
The accepted lethal level of shock current passing through a person need only be 50mA or 1/20 A. This means all metalwork must be at near zero volts so under fault conditions all metalwork will rise to the same potential.
The inspection and testing of the full premises wiring system for modern installations should itself have taken into account the earth fault loop impedance and any earth electrode resistance. For older wiring systems, however, it is possible that the efficiency of the earthing and bonding may be questionable.
The installation of an additional circuit may not be earthed efficiently at source so a hazard can act-ually be introduced at any point on the new circuit.
It is not possible to assume that the existing system is always satisfactory in relation to the current requirements.
Further considerations
Although it is always advisable to derive the mains supply direct from the distribution board, this is not always possible and the security installer must therefore be alert when taking a connection from an existing circuit in order to be assured of its suitability.
There is a further need to be able to recognise three phase supplies when working in industrial and commercial premises as these have 400 volt potential. The implications of working alone, poor equipment labelling and badly lit working areas also need to be addressed.
The effect of bringing electrical safety within the scope of the Building Regulations is now becoming apparent and the complications and responsibilities becoming real.
The security installer in the long term will not only have to adjust to the rapid development of new technologies and integration with communications networks within the security industry but must also be able to become increasingly involved with mains compliance.
The need for the contractor to be able to demonstrate competence via a training assessment course – so that low voltage installations can then be signed off as compliant using a self certification route – will now become commonplace. Compliance with BS 7671 is needed to avoid prosecution. It's known as the real world!
Source
Security Installer
Postscript
Gerard Honey is a technical author with Tavcom Training. Contact him on gerard@honey9961.fsworld.co.uk
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