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Often the most effective flame retardant cables are halogenated because both the insulation and outer Jacket are flame retardant however once we need Halogen Free cables we find it’s typically solely the outer jacket which is flame retardant and the internal insulation is not.
This has significance as a result of whereas cables with a flame retardant outer jacket will typically move flame retardance tests with exterior flame, the identical cables when subjected to high overload or prolonged quick circuits have proved in college exams to be highly flammable and might even begin a fireplace. This effect is known and published (8th International Conference on Insulated Power Cables (Jicable’11 – June 2011) held in Versailles, France) so it is maybe stunning that there are not any frequent check protocols for this seemingly common occasion and one cited by both authorities and media as explanation for constructing fires.
Further, in Flame Retardant take a look at methods such as IEC60332 parts 1 & three which make use of an external flame supply, the cable samples usually are not pre-conditioned to normal working temperature but examined at room temperature. This oversight is necessary especially for power circuits as a end result of the temperature index of the cable (the temperature at which the cable material will self-support combustion in normal air) shall be considerably affected by its starting temperature i.e.: The hotter the cable is, the extra easily it will propagate fireplace.
It would seem that a need exists to re-evaluate current cable flame retardance test methods as these are commonly understood by consultants and consumers alike to supply a dependable indication of a cables capability to retard the propagation of fireplace.
If we can’t trust the Standards what do we do?
In the USA many constructing requirements do not require halogen free cables. Certainly this isn’t as a end result of Americans aren’t wisely knowledgeable of the risks; rather the method taken is that: “It is healthier to have extremely flame retardant cables which don’t propagate hearth than minimally flame retardant cables which may unfold a fire” – (a small fireplace with some halogen could additionally be higher than a big fireplace with out halogens). One of the most effective methods to make a cable insulation and cable jacket extremely flame retardant is through the use of halogens.
Europe and plenty of nations around the globe undertake a different mentality: Halogen Free and Flame Retardant. Whilst this is an admirable mandate the truth is rather completely different: Flame propagation checks for cables as adopted in UK and Europe can arguably be said to be much less stringent than a number of the flame propagation exams for cables in USA leading to the conclusion that common tests in UK and Europe might simply be exams the cables can move somewhat than tests the cables ought to cross.
Conclusion
For most flexible polymeric cables the choice remains at present between excessive flame propagation performance with halogens or reduced flame propagation performance with out halogens.
Enclosing cables in metal conduit will reduce propagation at the point of fire however hydrocarbon based mostly combustion gasses from decomposing polymers are probably propagate via the conduits to switchboards, distribution boards and junction boxes in other parts of the building. Any spark such as the opening or closing of circuit breakers, or contactors is likely to ignite the flamable gasses resulting in explosion and spreading the fire to another location.
While MICC (Mineral Insulated Metal Sheathed) cables would supply a solution, there may be often no singe perfect reply for each installation so designers want to gauge the required efficiency on a “project-by-project” foundation to resolve which expertise is perfect.
The major significance of fireplace load
Inside all buildings and initiatives electrical cables provide the connectivity which keeps lights on, air-conditioning working and the lifts running. It powers computer systems, workplace tools and supplies the connection for our phone and computers. Even our cellphones want to connect with wireless or GSM antennas which are connected to the telecom network by fiber optic or copper cables. Cables ensure our safety by connecting
fire alarms, emergency voice communication, CCTV, smoke shutters, air pressurization followers, emergency lighting, hearth sprinkler pumps, smoke and warmth detectors, and so many different options of a contemporary Building Management System.
Where public security is important we often request cables to have added safety features such as flame retardance to ensure the cables do not simply unfold fire, circuit integrity throughout hearth in order that essential fire-fighting and life security equipment keep working. Sometimes we could recognize that the combustion of electrical cables produces smoke and this can be poisonous so we name for cables to be Low Smoke and Halogen Free. Logically and intuitively we expect that by requesting these special properties the cables we buy and install will be safer
Because cables are put in by many different trades for various applications and are mostly hidden or embedded in our constructions, what is commonly not realized is that the numerous miles of cables and tons of plastic polymers which make up the cables can represent one of the greatest fire hundreds in the building. This point is certainly worth considering more about.
PVC, XLPE, EPR, CSP, LSOH (Low Smoke Zero Halogen) and even HFFR (Halogen Free Flame Retardant) cable supplies are largely primarily based on hydrocarbon polymers. These base materials aren’t typically flame retardant and naturally have a excessive hearth load. Cable manufacturers make them flame retardant by including compounds and chemical substances. Certainly this improves the volatility of burning but the fuel content material of the base polymers remains.
Tables 1 and a couple of above compare the fire load in MJ/Kg for widespread cable insulating materials against some widespread fuels. The Heat Release Rate and volatility in air for these materials will differ but the gasoline added to a hearth per kilogram and the consequential volume of heat generated and oxygen consumed is relative.
The volume in kilometers and tons of cables put in in our buildings and the related fireplace load of the insulations is appreciable. This is particularly important in tasks with lengthy egress occasions like high rise, public buildings, tunnels and underground environments, airports, hospitals etc.
When contemplating fireplace safety we should first understand an important elements. Fire consultants tell us most fire associated deaths in buildings are attributable to smoke inhalation, temperature rise and oxygen depletion or by trauma caused by jumping in making an attempt to escape these effects.
Smoke
The first and most necessary side of smoke is how much smoke? Typically the bigger the hearth the more smoke is generated so something we will do to scale back the spread of fire will also correspondingly reduce the amount of smoke.
Smoke will contain particulates of carbon, ash and different solids, liquids and gasses, many are toxic and flamable. In explicit, fires in confined areas like buildings, tunnels and underground environments trigger oxygen levels to drop, this contributes to incomplete burning and smoldering which produces elevated quantities of smoke and toxic byproducts including CO and CO2. Presence of halogenated materials will launch toxic Halides like Hydrogen Chloride along with many different poisonous and flammable gasses in the smoke.
For this cause frequent smoke exams performed on cable insulation materials in large three meter3 chambers with plenty of air can provide misleading smoke figures as a result of full burning will typically launch significantly much less smoke than partial incomplete burning which is most likely going in apply. Simply specifying IEC 61034 with a defined obscuration value then pondering this can present a low smoke environment throughout fireplace might sadly be little of help for the people actually involved.
Halogens, Toxicity, Fuel Element, Oxygen Depletion and Temperature Rise
It is concerning that Europe and other nations undertake the concept of halogen free materials with out properly addressing the topic of toxicity. Halogens launched throughout combustion are extremely toxic but so too is carbon monoxide and this isn’t a halogen gas. It is frequent to name for halogen free cables and then allow the usage of Polyethylene as a result of it’s halogen free. Burning Polyethylene (which could be seen from the desk above has the very best MJ fuel load per Kg of all insulations) will generate nearly 3 instances extra warmth than an equal PVC cable. This means is that burning polyethylene is not going to solely generate nearly 3 times more warmth but in addition consume nearly three times more oxygen and produce significantly extra carbon monoxide. Given carbon monoxide is liable for most toxicity deaths in fires this example is at finest alarming!
The gas elements proven within the desk above indicate the amount of warmth which might be generated by burning 1kg of the frequent cable insulations tabled. Certainly this warmth will accelerate the burning of different adjacent supplies and should assist unfold the hearth in a building however importantly, to find a way to generate the heat vitality, oxygen must be consumed. The larger the warmth of combustion the extra oxygen is needed, so by choosing insulations with excessive fuel elements is including significantly to at least 4 of the primary risks of fires: Temperature Rise, Oxygen Depletion, Flame Spread and Carbon Monoxide Release.
Perhaps it’s best to put in polymeric cables inside metal conduits. This will definitely help flame spread and minimize smoke because inside the conduit oxygen is proscribed; however this is not an answer. As stated beforehand, lots of the gasses from the decomposing polymeric insulations contained in the conduits are extremely flammable and poisonous. These gases will migrate along the conduits to junction packing containers, switch panels, distribution boards, motor control facilities, lamps, switches, and so on. On entering the gases can ignite or explode with any arcing such as the make/break of a circuit breaker, contactor, switch or relay inflicting the hearth to spread to another location.
Conclusion
The reputation of “Halogen Free” whereas ignoring the other poisonous parts of fireside is a clear admission we don’t understand the topic nicely nor can we easily outline the hazards of mixed poisonous parts or human physiological response to them. ร้านซ่อมเครื่องวัดความดัน is necessary nonetheless, that we do not continue to design with only half an understanding of the issue. While no good answer exists for natural based mostly cables, we are in a position to actually minimize these critically important effects of fireside risk:
One option possibly to choose on cable insulations and jacket supplies which are halogen free and have a low gas component, then set up them in steel conduit or perhaps the American strategy is healthier: to use extremely halogenated insulations so that in case of fireside any flame spread is minimized.
For most energy, management, communication and knowledge circuits there may be one full resolution obtainable for all the issues raised in this paper. It is an answer which has been used reliably for over 80 years. MICC cables can present a total and complete reply to all the issues related to the fire security of natural polymer cables.
The copper jacket, magnesium oxide insulation and copper conductors of MICC make positive the cable is effectively fireplace proof. MICC cables have no natural content so simply can’t propagate flame or generate any smoke. The zero gasoline load ensures no heat is added and no oxygen is consumed.
Being inorganic MICC cables cannot generate any halogen or poisonous gasses in any respect together with CO.
Unfortunately many widespread cable fire check strategies used today may inadvertently mislead individuals into believing the polymeric flexible cable products they purchase and use will perform as expected in all fire situations. As outlined on this paper, sadly this is most likely not right.
For more info, go to www.temperature-house.com
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