Abstract: A district heating line comprising an inner metal tube intended for the transfer of a heating medium and encircled by an insulating layer of foamed plastic. Arranged around the insulating layer is a moisture impenetrable protective tube. To enable an alarm to be given in the event of a fault in the line, elongated blocks are fixedly mounted on the outer cylindrical surface of the metal tube. The blocks are made of electrically insulating material. They each have at least one radially extending, outwardly opening channel on the outer surface thereof with the channels on adjacent blocks aligned with one another. The channels are dimensioned to accommodate the electrical conductor and position it at a fixed distance from the outer cylindrical surface of the inner metal tube. The conductor is secured in the aligned channels at the fixed distance from the outer cylindrical surface of the inner metal tube. A water soluble salt is incorporated in the electrically insulating blocks.

Abstract: A district-heating line comprising an inner metal tube intended for the transfer of heating medium and encircled by an insulating layer of foamed plastic. Arranged around the insulating layer is a protective tube. To enable an alarm to be given in the event of a fault in the line, there is fixedly mounted on the outer cylindrical surface of the metal tube, an elongated block which carries at least one alarm conductor, said conductor being grouted in a fixed position in an associated channel in the block by the foamed plastic insulating material. In this way, the alarm conductor can be fixed at a given distance from the metal tube, to facilitate the localizing of a fault.

Abstract: A monitoring arrangement for monitoring a change from a normal condition of any one of a plurality of condition sensing devices. It includes a common two conductor circuit connecting the condition sensing devices. A central monitoring apparatus is connected to the common two conductor circuit and supplies current to the circuit. Each of the condition sensing devices includes a device for limiting the amount of current flowing therethrough from the common two conductor circuit; a mechanism to detect and to react to any change from a normal condition being sensed; and a mechanism to interrupt the current to at least all following condition sensing devices in the circuit upon reaction of the condition sensing device to a change in a condition being sensed. An apparatus is formed as part of the central monitoring apparatus for measuring and indicating a magnitude of current being supplied to the common two conductor circuit at any given time.