t is disclosed herein a tight prefabricated cylindrical or polygonal manhole-like junction box 1 made from steel or strong thermoplastic material and destined to be embedded under the ground or at the ground level and be used, as an accessible intermediate housing in optical fibre cabling networks, in which housing there are connected underground piping wherein cables are positioned for protection and easy replacement thereof. By virtue of the absolute tightness it provides, said manhole is characteristically called "sealed manhole" and can operate as a junction box for underground optical connections and receive, onto adequate supports, whatever accessories and subsystems for the organizing and storage of welded optical fibres. Tightnessis obtained by two caps 2,3 positioned on bases having sealing rubbers, and the airtight interconnection of the manhole and underground piping via adequate mechanical connections 8; introduction of compressed air in the interior of the junction boxis accommodated by valves positioned onto the forgoing caps. Additionally, the two caps permit high-safety access to authorized persons, only; opening is achieved with a special tool unscrewing the safety screws of the external cap and proper keys unlocking the padlock or the safety lock being disposed inside the cap. Complementarily, there is the possibility of supervising the manhole condition or any possible attempted opening thereof by unauthorized persons, via sensing elements controlling the inside pressure. The properties of the "sealed manhole", in combination with the installation method of the cables and the special accessory facilitating the temporary interconnection of the piping inside thereof, provide great facilities and fast development of the telecommunication network infrastructure with optical fibre cables.
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