FAQ protection aim 3: Function maintenance
If there is a fire, the maintenance of the electrical functions of safety-relevant systems guarantees the availability of the safety equipment and must be guaranteed at all times. We can answer all your questions about the third protection aim here.
Function maintenance systems
- Can cables with function maintenance be routed in one cable tray with cables for the general power supply? Is mixed assignment permitted?
From a fire protection point of view, mixed assignment is possible. However, cables for general power supply and cables for function maintenance may not be routed directly adjacent to or on top of each other. During a fire, there may be mutual negative influencing of the cables, meaning that the cable function maintenance may not be achieved safely. We recommend a clear separation of cables with function maintenance from cables of the general power supply through the mounting of separating retainers.
In so doing, all the installation parameters named in the appropriate testing document must be complied with.
- Why must cable systems for function maintenance, e.g. cable trays, be the top installation?
The positioning of the cable system as the top installation ensures that there is no negative influencing from surrounding components in case of fire. The cable trays cannot be destroyed through route for the general power supply, pipes or ventilation lines, which can fail mechanically and possibly deform or fall down.
- Is it possible or permissible to create free-standing vertical ladders for function maintenance?
From a fire protection point of view, the free-standing mounting of vertical ladders for function maintenance is not possible or permitted. Vertical ladders are not tested specially for function maintenance, but the test results for the cables routed on the ceiling with clips are transferred to the vertical routing with vertical ladders according to the testing standard DIN 4102 Part 12. As with the tests under the ceiling, the cables are also installed directly in front of the building section (ceiling or wall) when installed on vertical ladders on the wall. This mounting situation does not occur if the cables are mounted on free-standing vertical ladders. The ambient conditions of the cable are no longer comparable to the testing parameters when cables are routed with clips under the ceiling. For this reason, there is no basis for an evaluation of free-standing vertical ladders for function maintenance.
- Is it possible or permissible to mount free-standing vertical ladders for function maintenance on light-duty partitions?
Mounting in front of a light-duty partition is theoretically possible if an appropriate fire protection classification is available for the wall. However, direct fastening of the vertical ladder on the partition is not possible. The structure of the wall does not allow fastening of the vertical ladders as required by the proof specifications.
However, it is possible to install vertical ladders for function maintenance directly in front of a light-duty partition if certain installation aspects are taken into account. Particular attention must be paid to the fastening of the vertical ladders on the floor and on the ceiling. In addition, special position fixing of the vertical ladders to the stands of the light-duty partition is required. For this type of mounting, the appropriate design options must be reviewed individually. Based on already implemented mounting of vertical ladders in front of light-duty partitions, OBO Bettermann can support you with appropriate suggestions for possible mounting.
- May cables for function maintenance be routed in steel armoured pipes?
Routing of cables for function maintenance in steel armoured pipes is permitted if a general construction test report is available as proof for this routing variant. This is usually issued in the name of the appropriate cable manufacturer.
With regard to the available pipes, the test reports refer to the standard EN 61386 Part 1. As the OBO Bettermann pipes correspond to the named standard, use of the pipes is always possible and approved for this routing variant.
Note: Only horizontal cable routing in steel armoured pipes is permitted.
- May multiple cables with function maintenance be routed together in a clip?
If the general construction test reports of the cable manufacturers contain data on the bundling of cables, then the bundling of multiple cables in a clip is possible and permitted. Refer to the appropriate general construction test report for information regarding the maximum number of cables per clip and the spacing of the clips.
- How and with which cables can electrical function maintenance be implemented in cases of fire?
There are two basic options to be implemented for electrical function maintenance.
One option is the routing of cables without any fire protection requirement in so-called "Fire protection ducts" or similar enclosures made of appropriate fire protection plates. During a fire, these protect the cables against direct flaming and thus secure the function of the cables.
The other option is the use of "cables with integrated function maintenance". The construction of these cables is specially designed for direct flaming during a fire. During a fire, the burning insulation material of the cables forms a protective ash layer. In this way, it ensures that the wires do not touch each other and that there is also no contact to the installation material. This safely prevents a possible short-circuit. These cables may only be routed together with appropriately tested routing systems, such as with clips, on cable trays, in grouped supports or also vertically with vertical ladders.
- May cable trays for function maintenance be fastened with cable trays for the general power supply jointly on a suspended support?
With regard to the function maintenance, a negative impact through surrounding components during a fire is not permitted. This cannot be excluded if the cable trays are mounted jointly on a suspended support. In general, considerably more cables are inserted in cable trays for the general power supply as in cable trays for function maintenance. From a mechanical point of view, this represents an unpermitted load of the joint support system. For this reason, cable trays for function maintenance and cable trays for the general power supply should always be fastened on separate suspended support.
- May cable trays for function maintenance be mounted on a stand-off support structure on the floor?
For support structures stood off on the ground, there are no testing proofs available. This means that such a mounting variant is not permitted with regard to function maintenance.
Stood-off support structures are always subjected to mechanical pressure, which should be regarded extremely critically for steel products in case of fire. An evaluation of such loads during a fire is almost impossible.
To implement a possible stand-off support construction for function maintenance, an individual observation of the appropriate design options is required. Here, in particular, the constructive design and the height of the stand-off must be regarded in combination with all other mounting parameters.
- What are the requirements for the fastening of sections for function maintenance?
All the fastening materials (anchors) must always have an appropriate fire protection proof with reference to the appropriate fastening substrate (concrete, masonry). The various proofs contain information on the maximum approved load during a fire and for mounting.
- Is additional securing of the brackets with a threaded rod always required?
With the standard support structures for function maintenance (cable routing on cable trays and cable ladders), securing of the brackets with a threaded rod is required. How this securing must be designed exactly can be found in the appropriate proof of the routing system.
This differs between the so-called "cable-specific support structures". There are variants in which no additional threaded rod lock of the brackets is required. However, there are also routing variants in which this is required. Refer to the appropriate proofs to determine whether and in what design threaded rod securing is required.
- What is the difference between standard support structures and cable-specific support structures for function maintenance?
The testing standard DIN 4102 Part 12 defines and describes the following standard support structures:
- Cable routing on cable trays
- Cable routing on cable ladders
- Cable routing with individual clips
- Cable routing with clamp clips and long troughs on profile rails
The purpose of the standard support structures is a transmission of the test results of the cables. This leads to the fact almost all the general construction test reports of the cable manufacturers contain the results for standard support structures.
There are "surveyor's comments" available as proof with regard to function maintenance. However, they are not sufficient on their own as a proof of suitability in the sense of the construction regulations. In addition, a general construction test report of the cable manufacturer is required.
All the tested routing variants, which do not correspond to the definitions of the DIN 4102 Part 12 for standard support structures, are termed so-called "cable-specific support structures". It is not possible to transfer the test results for these systems. A general construction test report is always required as proof. Besides the structural description of the system, this also contains all the mounting parameters as well as the cables tested and classified together with the system.