No smoke without fire... (Guide to low fire hazard cables)
Many building projects now call for the use of cables that, in the event of a fire, are less hazardous to people when they burn. There are two key features &#; reduced smoke emission to minimise hazards from smoke inhalation and aid evacuation, and no or minimal halogen combustion products which are highly toxic. These must not be confused with Fire Retardant cables, which are designed to continue to perform for extended periods in the event of fire eg. in voice evacuation systems, and have an altogether quite different and much more complex construction.
The original cause of the problem is that the most commonly used cable insulating and jacketing material is PVC. Advantages are its cheapness, and that, with the addition of various elastomers, it can be made extremely flexible and remain so at lower temperatures. Disadvantages are that it&#;s nasty when it burns, as it produces considerable amounts of smoke and releases toxic halogen compounds.
For deployable cabling therefore, PVC remains the main jacketing material. For lowest cost there is plain PVC, for improved flexibility there is "Arctic" grade &#; most commonly used on mains cables &#; and then there are more complex proprietary compounds used on many audio and video cables where exceptional flexibility is required and where a "semi-matt" ("satin") surface finish is required.
So, to create cables that are less hazardous in the event of fire, various compounds have been developed. These are typically described as "low smoke, zero halogen" or "low fire hazard". The bad news is that they lack flexibility &#; but as cables made from these are going to be in ducts or ceiling voids, that&#;s not really a problem. They are obviously not recommended for deployable use!
Some confusion is caused as a result of some manufacturers using four-letter acronyms for these types which they have registered as trademarks, but which have become commonly used to describe the cable style. "LSOH", the best known, is a trademark of Pirelli General PLC, one of the earliest developers of this kind of material. Most other meaningful combinations of these letters (including Z for zero or N for no instead of O) are also registered trademarks. Consequently Canford cannot use these in the catalogue &#; instead we use our own mark &#; "LFH".
Part 1 (BS EN -1) applies to single wires (cables) and requires a vertical flame test with a maximum flame climb of 450mm
Part 2 (BS EN -2) applies to very thick copper conductors and is not relevant to audio, video, data and low level control cables
Part 3 (BS EN -3) applies to &#;bunched&#; wires (cables). This part of the specification is intended to apply to large cable bundles in building cable ducts. (Additional specifications apply to air conditioning ducts or similar where a forced air supply is present.) Advice should be taken from local regulators to determine if this part applies to your installation.
All PVC, LFH and Special PUR cables manufactured for Canford by Draka, conform to the requirements of BS EN -1 / IEC -1 and can be referred to as "Low Fire Hazard" within the context of this specification (provided the installation is not required to conform to Part 3)
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However - for a cable to be described as "Low Smoke and Halogen Free" it must additionally meet the requirements of:
IEC -1 Halogen and Acid Gas Free IEC -2 Halogen and Acid Gas Free IEC 3m3 Smoke testAll cables manufactured for Canford by Draka and described by us as "LFH" meet these requirements and can be described as "Low Smoke and Halogen Free".
Note: The higher specification IEC -3-24 test is no longer valid. It has been replaced by the Construction Production Regulation set of "Euroclasses" denoting the different levels of reaction to fire.
All Canford PVC, LFH and PUR cables falling under the terminology "telecommunications cables" (audio, video, data) can be classed as &#;Low fire hazard&#; within the guidelines of BS : .
1 Products of combustion of polyethylene do not include any halogens, therefore the resulting smoke is halogen-free
2 Fillers are the co-polymers used to retard and control the combustion.
Certification should be sought from trade mark holders or users of the above terms that cables conform to the specifications listed.
Common Fuse Box Problems What is a fuse box? A fuse box is a type of electrical cabinet in which fuses, and circuit breakers are used to protect the wiring system from overloads, short circuits and ground faults. Fuse boxes help to distribute electricity more efficiently, with safety as a primary concern. Before we dive into the most common fuse problems, lets have a look at how a fuse box works. How does a Fuse box work? A fuse is designed to "blow" (or melt and separate the fusible link) under too high of an electrical current. A circuit breaker, on the other hand, interrupts electrical service through the use of tripped switches. These two main types of protection are then complemented by various other forms of devices, such as ground fault protection, arc fault protection and surge protectors. Fuses are typically divided into two types: cartridge fuses and link or cable fuses. The cartridge fuse is a small tube that holds the fusible metal link in place. After the circuit has become overloaded or shorted, the link melts and the circuit is broken. The tube then cools down again to reform the link, allowing normal operation to resume. The Most Common Fuse Box Problems The average person can notice signs of a failing fuse box. You don&#;t need to be a qualified electrician to understand you may have a problem on your hands. The two most common symptoms are: An overloaded circuit which will blow the fuses in question. As a result, this will cause any associated devices to disconnect. Lastly, the smell of burning is another clear indication of a faulty fuse, as well as the smell you will notice burn marks on the fuse box. If you notice either of these signs within your premises, it&#;s a clear sign of a problematic fuse box. To resolve these issues, you must contact a qualified electrician. What causes the most common fuse box problems? Faulty Appliances: A faulty fuse box can be the result of a single appliance. For example, a hairdryer, kettle, laptop, or any other appliances in use. Regardless of the appliance, any electrical fault present can lead to your fuse box tripping repeatedly. The way to identify the issue is by disconnecting all appliances and then plugging them back in one at a time until the circuit trips. Poor Wiring: Fuse boxes generally undergo a lot of maintenance work during their lifespan. This continuous maintenance can lead to the installation of poor wiring or installation of the wrong size wire. Both of these examples pose major risks such as, electric shock or electrical fire. All wiring issues must be investigated and dealt with by a professional electrician. In addition, if poor wiring is the reason for your faulty fuse box, it must be dealt with as top priority. Overloaded Circuits: Present day buildings are generally full of electrical devices, and this can lead to significant strain on your fuse box. In addition, this highly noticeable when extension leads are in use. www.nmcabling.co.uk
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