Fire resistant cables. Explanation of the Belgian regulation.
What about the regulations for fire-resistant cables? How do RGIE/AREI and fire tests match up?
Article 104 of the AREI prescribes under point 03.e.4) that vital circuits must have the characteristic FR2 or equivalent, whereby in case of fire they must remain operational for at least 1 hour.
FR2 according to NBN 713-020 Addendum 3
The table with the classification of the electrical conductors according to their fire performance at the beginning of Article 104 (point 01.a), describes this characteristic FR2 as follows: "FR2 relates to a test which allows assessing the duration of time during which the maintenance of the electrical function is ensured (cable tested with support system and fastening)". This description refers to the test from the Belgian test standard NBN 713-020 "Fire fighting. Fire performance of building materials and products. Fire resistance of building materials" and its Addendum 3 that is specifically dedicated to electric cables.
NBN 713-020 Addendum 3
What exactly does this test standard NBN 713-020 Addendum 3 assess? - There are some misunderstandings about this due to the test set-up itself.
Unlike other fire tests, the cables are not individually fixed in a standard lab set-up, but the set-up in the furnace mimics reality as well as possible. This means that the cables are placed on a cable support and then fixed as the installer would. Once everything has been set up, the fire test is carried out according to standardized parameters. It is important to realize that the test only records the fire resistance performance of the cables. If the cable has passed the test - that is, it remains operational for 1, 1.5 or 2 hours, it then obtains the characteristic FR2 with the corresponding indication of the duration of the fire resistance: Rf 1h, Rf 1,5h or Rf 2h.
Of course, cable support and fastenings also undergo the influence of the fire during the test, but the test according to NBN 713-020 Add.3 does not register their behaviour and therefore does not appreciate it. Hence, the characteristic FR2 is limited to cables. The fire resistance of the cable support and fastenings must be tested and expressed in accordance with other, relevant standards such as DIN 4102-12.
It needs little explaining that fire resistance of the cable and that of the support system must be aligned as the total fire resistance duration of the whole installation (cable on a cable support with fixings), will be the one of the weakest element. A fire resistant cable with, say; characteristic FR2 Rf 1,5h must remain operational for one and a half hours in the event of fire. Suppose that the cable lies on a cable tray with a fire resistance of 30 minutes: after 30 minutes that cable tray will most probably start to go, and it will no longer support the cable, possibly causing the cable to be torn loose.
FR2 or equivalent?
The sentence "Conduits ... of the type with characteristic FR2 or equivalent" used in the AREI may be construed as if cables complying with standard DIN 4102-12 are allowed. In fact, establishing the comparability of test standard NBN 713-020 Add.3 and its classification FR2 with DIN 4102-12 proves rather difficult, since the only common element is the use of the same, internationally recognized temperature curve ISO 834. All other test conditions in these 2 standards, such as the heat source, the methods of cable installation and mounting, their deformations, the control circuit, the sampling of the cable sections to be tested, ... differ so that it is impossible to consider them as equivalent.
Moreover, one should take into account that the additional legislation such as the Basic Standards, the regional and local decrees etc., rely mainly on the characteristic FR2 and therefore on the testing standard NBN 713 020 Add.3.