I wouldn't worry about them being bunched, maybe try as much as possible to leave a couple of inches if possible , never seen an install affected by interference or induction others may differ.
Instrumentation, signal, and telecommunications cabling should always ideally be separated from power cabling. This includes cabling used for fire alarm systems.
As well as meeting minimum bend radii requirements, cable management systems are also usually required to carry wiring for mains power, lighting and other electrical services such as building controls, fire and security systems. BS5839 Fire detection and fire alarm systems for buildings – Part 1 Code of Practice for system design, installation, commissioning and maintenance, in its 1988 edition stated that fire alarm cables should not be readily exposed to electromagnetic disturbance, possibly emanating from other cables. BS5839 still states in section 26.1 that ‘The circuits of fire alarm systems need to be segregated from the cables of other circuits to minimise any potential for other circuits to cause malfunction of the fire alarm system arising from:…electromagnetic interference to any fire alarm circuit as a result of the proximity of another circuit’. Therefore, while it is recognised that this ideal situation is not always possible in practice, especially where alarm cables are retrofitted, none-the-less, fire alarm cables should, if possible, always be segregated from cables for other systems. Installation of cables should be in accordance with good practices recommended in the IEE wiring regulations. Also, wherever possible, it is sensible to route fire alarm system cables through low fire risk areas. They should be PVC sheathed if installed in damp or corrosive environments, or where there is risk of mechanical damage. The minimum bending radius as defined for each type of cable has to be respected. It is important to note that any later re-routing, or addition, of cables on to cable trays, conduits or other cable management system already occupied by electrical cables of a different kind may adversely affect an existing cable segregation arrangement. In turn, this could result in compromised fire prevention.
Other issues to consider include the following:
Compliance with relevant BS and IEE Regulations for segregation of services.
Conductor rating for alarm load / volt drop requirements.
Earthing (in accordance with IEE Regulations).
Mains voltage power supply to control equipment in accordance with the relevant regulations
Protection provided for surface laid insulated and sheathed cables, where there may be mechanical damage, or attack by rodents, or where cables are installed less than 2.5m from the floor.
Mineral insulated (MICC) cables to be provided with PVC sheaths in corrosive or damp situations.
More specifically, the IEE Wiring Regulations (BS 7671) also demands segregation of electrical circuits. These need to be kept apart (segregated) and this is achieved through category classification. Amendments published in 1997 resulted in simplification, and there are now only two categories (Voltage Bands I & II). Voltage Band I covers voltage levels so low that they cannot cause dangerous electric shocks. As such, Voltage Band 1 relates only to extra-low voltage (ELV) circuits, such as control, alarm and signalling circuits, as well as telecoms. Voltage Band II covers all voltages - 230/400 V (240/415 V) - used in electrical installations not covered by Band I. BS 7671 prohibits Band I and Band II cables sharing the same cable management system (trunking enclosure etc, or multicore cable). There are exceptions provided that every cable (or each conductor in a multicore cable) is insulated for the highest voltage likely. Otherwise, conductors relating to Voltage Bands I & II must be separated by an earthed metal screen or installed in separate trunking / ducting compartments. Foil screens have good screening properties and are light in weight, and are often ideal for use with fire alarm cables. Pliable fire alarm cables today unusually use metal foil / polyester tape or the drain wire screening system. Alternatively, such conductors must be laid in a partitioned cable tray, or separate conduit / ducting systems must be provided for each Voltage Band system. BS7671 states: ‘Fire alarm and emergency lighting circuits shall be segregated from all other cables and from each other in accordance with BS5839 and BS5266’, and BS 58398 requires that that fire alarm cables must be separated from all others. Moreover, IEE Guidance Note 4 refers to BS5266, of which Section 8.2.1 states: ‘Cables used for the connection of an escape lighting luminaire to the standby power supply should…possess inherently high resistance to attack by fire…’. BS5266 also states that PVC cables in trunking (steel or PVC) and PVC/SWA cables will need additional fire protection. In all cases, they should not be affected by electrostatic / electro-magnetic fields. Another aspect is that where electric circuit outlets from both Voltage Bands share a common box or switchplate, the relevant connections must be segregated by a partition, and if the partition is metal, it must be earthed. As always, whichever necessary cable segregation system is chosen, space should be left inside enclosures or compartments to allow the laying of further cables at a later dated if required. In short, the gist of segregation, as far as BS5839 is concerned, goes far beyond EMC. It is a requirement to preserve the integrity of life safety systems from mechanical damage from other cables during installation, or from faults on other circuits during service.
I have a guide to bs 5839 on the pc here which I could send you now or I should have both in full at the office which I could scan and send on. (Not be back to office untill middle of next week).
If you are interested pm me an email address.
As long as its T&E and not singles then there is no problem as the T&E has a Nuteral or return path incorperated into it and so hence there will be no electromagnetic effects to consider
Reply to fire alarm and power in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net
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