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What is the effect of temperature on the resistance of wires?
The resistance of the wires changes as a function of temperature. According to the ISO curve, the temperature of the PH30 cable operating in fire conditions will be 822°C after 30 minutes and its resistance will increase 4.5x! The temperature of the PH90 cable after 90 minutes will be approximately 955°C and its resistance will increase by almost 5.3x! This should be taken into account when designing the installation and appropriate safety factors should be adopted. The resistance of the cable affects voltage drops and, consequently, whether the device will operate in hazardous conditions or not. Voltage drops can be compensated by increasing the cross-section of the conductors.
How to read and what does the IK protection degree mean?
The PN-EN 50102 (PN-EN 62262) standard provides a classification of the degrees of protection provided by enclosures against external mechanical shocks for devices with a rated voltage not exceeding 72.5 kV. The definitions of the degrees of protection and their markings, the requirements for each marking and a description of the tests performed to check whether the housing meets the requirements of the standard are provided.
The standard presents a classification from 0 to IK10, where IK0 means no protection and IK10 means resistance to an impact with an energy of 20J (the impact of a steel hammer or a ball weighing 5 kg falling on the housing from a height of 40 cm).
Did you know that:
A change to the above has recently been published. standard, which introduces, among other things, a new protection level IK11 (resistance to a 50J impact energy!).
What does the VAD coverage category mean?
In the EN 54-23: 2010 standard, apart from the division due to the working environment, a division of devices according to the coverage category has been introduced:
"C" category - ceilling mounted devices
"W" category – wall mounted devices
"O" category – open class devices
In [1], the division according to the coverage category has been characterized. For category C signaling devices, the manufacturer must specify the maximum mounting height: 3 m, 6 m or 9 m and the diameter (in meters) of the cylindrical area that is the operating range of the device installed at ceiling height, where the signaling device achieves the required light intensity. For example, the designation C-3-6 means that the VAD mounted at a height of 3 m provides the required light intensity in a cylinder with a diameter of 6 m and a height of 3 m.
For category W devices the maximum height for mounting the device on the wall (minimum 2.4 m) and the width (in meters) of the cubic area where the required luminance complies with the standard have to be specified. For example, the designation W-2.4-4 means that the VAD mounted on the wall at a height of 2.4 m will provide the required light intensity in a 2.4 x 4 x 4 m space.
The signaling devices manufactured by W2, which have an optical element certified in accordance with EN 54-23: 2010, have been classified as category O devices. This means that they can be mounted both, on ceiling and wall and the declared coverage area is represented by a photometric solid. The exact shape of the solid for devices has been made available on the W2 website.
[1] Borysewicz Jarosław, Stępień Paweł, Chołuj Łukasz, Requirements, test methods and criteria for assessing optical signaling devices (VAD). The method of measuring light distribution, BiTP Vol. 44 Issue 4, 2016, pp. 159-164
Where and why are VADs used?
VADs should be used wherever there is a possibility that hearing impaired people are present or hearing protectors are used. Relevant provisions regarding the use of VADs can be found in CEN/TS 54-14:2004 Fire detection and fire alarm systems - Part 14: Guidelines for planning, design, installation, commissioning, use and maintenance
"In zones where acoustic signals may be ineffective, e.g. due to the background noise being too high, hearing impaired among users, or where hearing protectors are probably worn, in addition to acoustic signals, optical signals should be used"
VADs should only be used to supplement acoustic alarm devices and should not be used alone.
“Optical fire alarm devices should only be used in addition to acoustic alarm devices and should not be used alone. Each optical fire alarm should be clearly visible and distinguishable from other optical signals used in the facility.”
What is an visual alarm device (VAD)?
An Visual Alarm Device is a device that generates a flashing light intended to signal a fire hazard to persons in the building.
