In essence every non-domestic building will have some form of electrotechnical fire safety system installed within it which requires a mains power supply or multiple mains power supplies.
These systems could be fire detection & fire alarm systems, voice alarm systems, emergency voice communications systems (disabled refuge) and more recently introduced evacuation alert systems.
The mains power supplies obviously need to comply with BS 7671 however as they form an integral part of the fire safety system one needs to ensure that compliance with the relevant standard for the fire safety system e.g., BS 5839-1 in the case of fire detection & fire alarm systems is achieved.
In any instance where any conflict is identified between BS 7671 and the relevant fire safety system standard such as BS 5839-1, then the fire safety system standard takes president.
This article covers the headline compliance considerations that present themselves to the electrician installing these circuits.
Power Supplies and Means of Isolation
The circuit to the system needs to be uninterrupted and dedicated solely to the fire safety system and the unnecessary use of residual current devices is not permitted.
The number of protective and isolating devices between the origin of the supply and the means of local isolation to the fire system needs to be
kept to a minimum. In practice this would comprise of a dedicated circuit emanating from the first electrical distribution board in the buildings electrical distribution system. In very large buildings where there are several power supplies needed for the fire safety systems then this will be impracticable, and it is more likely that supplies will be derived from more local distribution boards. In such instances this is a variation to the standard and as such needs to be agreed and recorded, dealing with variations is covered further in this article.
Each power supply needs to have a local means to safely isolate the supply to the fire safety equipment. Selection of an isolator is important as many electricians select switches that do not afford isolation as defined in BS 7671. Isolation needs to be afforded for the safety of those undertaking ongoing system maintenance.
The means of isolation needs to be such that it must be done with a tool e.g., a key type of action and isolation not able to be made by the mere pushing of a switch. This is to prevent the power to the fire safety system being isolated in error or maliciously.
All power supplies need labelling at each local isolator with specific wording that is prescribed within the standard so in the instance of a fire alarm “FIRE ALARM DO NOT SWITCH OFF” this label also needs to be applied to the protective device for the dedicated circuit. This is commonly understood by electricians, however what is often an oversight is the need to label all protective devices going back to the origin with the wording “WARNING THIS SWITCH ALSO CONTROLS THE SUPPLY TO THE FIRE ALARM SYSTEM”. The reasoning for this is that the isolation of a supply to a sub board which houses the dedicated circuit could inadvertently disconnect the mains power supply to the fire safety system.
Cables, Wiring and Connections
All mains power supply circuit cabling needs to match the colour of the ELV fire safety system cabling which is normally red so that it is distinguishable from other electrical circuits. The LV mains power supply cabling shall be segregated from the ELV fire system cabling so particular attention is needed when entering the item of fire safety system equipment in that it needs to be a separate cable entry to the ELV system cabling.
All cabling needs to be fire resistant and in buildings over 30m in height that are not protected by a sprinkler system or buildings where there is a phased evacuation strategy then the fire resistance of the cable needs to be enhanced from the standard rating of 30 minutes to 120 minutes.
Methods of cable support need to be non-combustible and withstand similar temperature for a duration to that of the cable. The cable needs to be supported at intervals strictly in accordance with the cable manufacturers recommendations.
In the unlikely event that a joint is required within the mains power supply circuit then the method of jointing should withstand similar temperature for a duration to that of the cable and the box in which the joint is made shall be clearly labelled “FIRE ALARM”.
Cables which pass through walls, floors, and surface cables below 2m from the finished floor level need to be mechanically protected. This does not apply to steel wire armoured cabling and mineral insulated compound cabling.
In instances where cables pass through external walls, they need to be contained in a smooth bore sleeve of metal material sealed into the wall with the sleeve sloping downwards towards the outside and plugged using a waterproof compound to protect entry of rain, dust, or vermin.
Fire Stopping and Fire Sealing
Cables which pass through floors, walls, partitions, and ceilings need to be sealed using fire-stopping materials that ensure fire resistance of the construction is not materially reduced and that there are no spaces in which fire and or smoke can pass through and spread. The same applied to cables installed within containment such as trunking.
Inspection and Testing
All wiring needs to be inspected and tested in the usual way for insulation resistance, continuity, maximum circuit resistance and polarity with results recorded.
Variations
Any variations to the recommendations of the relevant standard e.g., BS 5839-1 in the instance of mains power supply circuits supplying of non-domestic fire detection & fire alarm systems need to be recorded.
It is important for the electrician to understand that any variation needs to be agreed by all relevant parties prior to being introduced. Relevant parties include but are not limited to the fire system specialist, user, purchaser, enforcing authority or insurer.
It is not acceptable to introduce variations without this pre agreement and retrospectively record them without agreement. Such situations are therefore not classed as an agreed variation and fall into the category of a defect.
Documentation and Certification
The electrician needs to produce as fitted drawings which detail the following:
• the positions of all power supply equipment.
• the type sizes and actual routes of all cables.
On completion of work the electrician is responsible for the production of the usual BS 7671 certificate for electrical safety which is understood. What is not broadly understood is that to comply with the relevant fire safety system standard the electrician is to also complete an Installation Certificate in accordance with the recommendations of that standard with the extent of liability being the mains power supply circuit only. The purpose of this is to certificate compliance of the circuit with the said standard e.g., BS 5839-1 for non-domestic fire detection & fire alarm system mains power supplies or BS 5839-9 for emergency voice communication systems (disabled refuge systems).
Summary
As electrical certification bodies do not audit compliance of fire safety system standards as part of the electrical assessment, then compliance with fire safety standards is not being undertaken and issues raised with electricians by technical assessment officers.
Unfortunately, this results in electricians not fully understanding matters of compliance for these circuits and inadvertently delivering defective work and not producing the relevant documentation and certification for what is an intrinsic part of a fire life safety system. Hopefully this article raises further awareness in this area.
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