High Reliability, Low Cost – Loop Technology for Voice Alarm Systems
The loudspeakers are still usually connected to a voice alarm system via spur technology, which carries a high risk of wire breakage or short circuit. DIN VDE 0833-4 A / B cabling can be used in systems in order to minimize this risk. In contrast to fire detection technology, loop wiring technology itself has not yet been established as the standard in the area of voice alarm systems (VAS), because this area has other requirements, based on higher power. The new VARIODYN D1 Loop Technology from ESSER represents a giant step forward.
Innovation in the Area of Voice Alarm Systems
Some manufacturers of professional voice alarm systems and electro-acoustic emergency warning systems are currently working on loop technology for 100 V loudspeaker connections. Usually, loudspeakers are still connected to the voice alarm system through spur technology. If a spur circuit is interrupted, however, all loudspeakers after the wire breakage would fail. During a short circuit, the entire spur circuit fails. In order to minimize risk in the case of wire breakage and short circuit, A/B cabling is used for systems based on DIN VDE 0833-4 (security levels 2 and 3), with half of the loudspeakers in a room operating on different loudspeaker lines. Thus, in a wire-to-wire short circuit (wire breakage, short circuit or ground fault), half of the loudspeakers in the relevant area remain in operation. So if the alarms sound at half power, the sound level is reduced by 3 dB, as long as the loudspeakers are correctly arranged. This level decrease is permitted in accordance with DIN VDE 0833-4 standards.
In contrast to fire detection technology, loop wiring technology itself has not yet been established as the standard in the area of voice alarm systems (VAS), because considerably higher power must be transmitted there. This results in higher demands for this area. It should be mentioned here that VARIODYN D1 Loop Technology uses a loop wiring system and not loop bus-technology as in fire detection technology. Moreover, complete system reliability for loudspeakers has still not yet been required in the relevant standards. A standard system built using today’s state-of-the-art technology in accordance with DIN VDE 0833-4 or EN 60849, an A/B or simple cabling in spur technology is sufficient, depending on the application.
Though loop technology requires additional isolator modules, they initially create additional costs. However, at second glance the entire system can be significantly less expensive, with cost savings in other places. So, depending on the application, cost-intensive E30 cabling can be partially avoided.
In regard to building ordinances, DIN VDE 0833-4 is not specified for required voice alarm systems in section 7.10.3. This may be waived for loop wiring systems of otherwise functional integrity, if it is guaranteed that forward and return lines are routed in separate cables, and that these cables are laid out separately in buildings with fire protection technology. In addition, it must be ensured that the intended function of the VAS is not affected by a single failure in these loop wiring systems. That might be the case in the technology described here.
How is VARIODYN D1 loop technology implemented?
The loop must always be monitored according to standards for wire breakage and short circuits. VARIODYN® D1 Technology achieves this with approved impedance monitoring. A short circuit represents a critical case here. To ensure the desired reliability, work on the loop must be performed using Loop Isolator Modules (LIM). These modules are supplied with voltage via the two-wire 100 V loudspeaker ring and are designed in accordance with EN 54-17 and VdS-approved. They constantly measure the current in the circuit. The short-circuited segment between the two insulators is separated from the circuit when the measured current is too high. The remainder of the loop wiring system is still in full operation. If each loudspeaker is equipped with a short-circuit isolator, this means that 100 percent reliability is achieved in case of a wire-to-wire short circuit.
They are mandatory for required voice alarm system building regulations in the respective federal states’ guidelines for circuit systems. Thus, a 30-minute alarm must be guaranteed, which can be realized by appropriate cabling. VARIODYN D1 Loop Technology represents an alternative to E30 cabling, because here a loop is fed on both sides and ensured according to EN 54-17 approved Loop Isolator Modules, so that functionality continues even during a short circuit. However, regionally, there is a waiver for E30 cabling through the use of loop wiring technology and individually-related different interpretations of the MLAR. Thus, we recommend clarification of the waiver for E30 cabling from the appropriate experts before implementation.
Fire detection and alarm technology has advanced since the existence of the MLAR (for example, regarding loop technology). The more advanced state-of-the-art, such as alarms via loop wiring, should also be considered in the next version of the MLAR.
(Horst Berger, functional integrity of alarm detector systems and VAS, pages 37-42, FeuerTRUTZ Fire Protection Magazine, issue 02/2013)
If a system of less than 100 percent reliability is desired and the system requires A/B cabling, this can be done as shown in the graphic above. A Loop Isolator Module (LIM) is always placed here between A and B segments of the loop wiring system.
Then, in case of a short circuit, only the affected A or B segment is detached. The system shown in this example would have the same security as an A/B cabling in spur circuit technology.
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