Circuit integrity refers to the operability of electrical circuits during a fire. It is a form of fireresistance rating. Circuit integrity is achieved via passive fire protection means, which are subject to stringent listing and approval use and compliance.Listing and approval use and compliance is the activity of adhering to all the requirements of installing andor using safetyrelated products and items in conformance with an active certification listing or approval that has been issued by an organisation that is accredited both for testing and product certification, such as those issued by Underwriters Laboratories, FM Global, American Nuclear Insurers, or the Deutsches Institut für Bautechnik DIBt. In concept, if a safetyrelated item, such as a fire door or a fire extinguisher, or a toaster is used in the same manner as the listing or approval states, and conforming to the intent of he associated testing, then use of the component or system complies with the listing. The listing or test is often cited by a regulation, such as a building code or a fire code, and as such is made law.
This concept is known as bounding in the nuclear industry. Products whose use is not mandated by any building codes or fire codes often lack a consensus test method. Unless there is a test standard in existence to prove the functionality and reliability of such a product, there can be no certification listing.National, governmental accreditors, such as Germanys Deutsches Institut für Bautechnik or Canadas SCC Standards Council of Canada can accredit laboratories, meaning that such laboratories must conform to national standards and rules of conduct in the discharge of their duties. Compliance is routinely tested by the accreditor through inspections, where random client files are audited to see that the laboratory followed all appropriate procedures. Accreditors can accredit laboratories for testing, as well as for product certification. In product certification regimes, the laboratory andor the accreditor as in the case of Germany become involved in witnessing the production of test materials, get copies of process standards, including chemical formulas and all details necessary to manufacture a product. Once the test product is made, it is shipped under seal to the laboratory for incorporation in the test.
FIREPROOFING
Providing fireproofing for cables, cable trays, or electrical conduit, is meant to keep cables operational during a specified fire exposure and time. This can be done in two different ways Cable coating is generally considered a fire retardant, which lowers the spread of flame and generation of smoke along the combustible cable jacketing. Some cable coating systems are able to achieve a measure of circuit integrity, which is demonstrated and quantified through certification listing and listing and approval use and compliance. An enclosure can be provided. Calcium silicate board can be used, or other methods including boards made of vermiculite, bonded and pressed with sodium silicate, flexible wraps made of ceramic fibre and rockwool, or ceramic fibre wraps treated with endothermic materials. In all cases, the installed configuration must meet the certification listing of the tested system. Alternatively, cables that achieve fireresistance ratings on their own can be used, such as Mineralinsulated copperclad cable, or MI cable. Mica insulated cables have also demonstrated a measure of circuit integrity for small cables.
Combustible cable jackets may catch on fire and cable fires can thus spread along a cable tray within a structure. This is easily prevented through the use of fireretardant cable jackets or intumescent or endothermic fireproofing or fire retardants.Proper housekeeping is important. Cable trays are often installed in hard to reach places. Combustible dust and clutter may accumulate if the trays are not routinely checked and kept clean.Plastic and fibreglass reinforced plastic are combustible and their effect is easily mitigated through the use of fire retardants or fireproofing.Ferrous cable trays expand with the increasing heat from accidental fire. This has been proven by the German OttoGrafInstituts Test Report III.Teitei Supplementary Test On The Topic Of Mechanical Force Acting On Cable Penetration Firestop Systems During The Fire Test, dated . October , to dislodge soft firestops, such as those made of fibrous insulations with rubber coatings. The same thing would apply to any silicone foam seals. This is easily remedied through the use of firestop mortars, as shown above, of sufficient compression strength and thickness. Also, some building codes mandate that penetrants, such as cable trays are run in such a manner as to avoid their contribution to the collapse of a firewall construction, or an occupancy separation.
TESTING AND CERTIFICATION
In Canada, testing is run in accordance with ULCS, as required by the local building code. Unfortunately, S is ill equipped to deal realistically with circuit integrity, particularly for enclosures. For circuit integrity cables, one simply uses a full scale wall panel test, loops the cables through the fire, energises the cables and quantifies the current carrying capacity of the cables during the fire.There are two ways of achieving circuit integrity. One may either choose mineral insulated or otherwise fireresistant tested for that purpose cables, or one may use an enclosure that was tested for that purpose. This is where grandfathered systems still find acceptance in certain parts in North America. A prime example of this is Canada, where the code indicates that of concrete coverage over or around electrical circuits is sufficient to obtain an unquantified duration of circuit integrity.There are often additional codes or sections of the same building code that have more specific requirements that apply to dwellings and special construction objects such as canopies, signs, pedestrian walkways, parking lots, and radio and television antennas.
No testing documentation exists to qualify this measure, according to the Institute for Research in Construction, a part of the National Research Council of Canada. of concrete, regardless of the conductor configuration, percentage fill, etc. is of course a judgment call. Inherently fire resistive cables can be tested to UL , Tests for Fire Resistive Cables, whereas enclosures for cables that are not inherently fire resistive can be tested to UL or USNRC Generic Letter , Supplement in North America, or BS in the United Kingdom or DIN in Germany.A building code, or building control, is a set of rules that specify the minimum acceptable level of safety for constructed objects such as buildings and nonbuilding structures. The main purpose of the building codes is to protect public health, safety and general welfare as they relate to the construction and occupancy of buildings and structures. The building code becomes law of a particular jurisdiction when formally enacted by the appropriate authority.Building codes are generally intended to be applied by architects and engineers although this is not the case in the UK where Building Control Surveyors act as verifiers both in the public and private sector Approved Inspectors, but are also used for various purposes by safety inspectors, environmental scientists, real estate developers, contractors and subcontractors, manufacturers of building products and materials, insurance companies, facility managers, tenants, and others.
THE MECHANICAL DUCTING PRECEDENT
The other grandfathered approach is drywall shaftwall systems. Drywall shaftwalls were tested as a flat wall, no corners, no turns. This approach has pretty much been negated for use around ductwork i.e. pressurisation and grease ducting, which are required to have a fireresistance rating since the adoption of the more suitable ISO test regime by ULC as well as Underwriters Laboratories, whereby a duct is suspended from a full scale floor slab and the enclosure is built around the duct or an inherently fire resistant duct is similarly tested without an enclosure, since it already contains a layer of insulation, for a more realistic D configuration and exposure. Drywall shaftwall systems were entirely grandfathered for this application and ceased to be legally representative of due diligence the instant a properly and purposely tested system with bona fide listings became available. The same thing applies to circuit integrity enclosures.
For the mechanical ductwork, a Canadian entrepreneur got ISO passed by the ULC Standards Council and then performed testing. This made all grandfathered systems legally indefencible.This has yet to occur in Canada for circuit integrity, but it has long been standard construction work in Europe and also in the US, through work done by UL and other laboratories. Since UL is accredited by the Standards Council of Canada in Canada and its listings are considered public record up all over North America including Canada, one is ill advised to use grandfathered systems for circuit integrity anywhere.Importantly, drywall shaftwall systems have only been qualified as straight walls in panel furnaces, not D enclosures with corners.Drywall is a common manufactured building material used globally for the finish construction of interior walls and ceilings.A drywall gypsum wallboard panel is made of a paper liner wrapped around an inner core made primarily from gypsum plaster, the semihydrous form of calcium sulfate CaSO·½ HO. The raw gypsum, CaSO· HO, mined or obtained from flue gas desulfurization FGD must be calcined before use. Kettle or Flash calciners typically use natural gas today. The plaster is mixed with fiber typically paper andor fiberglass, plasticizer, foaming agent, potash as an accelerator, EDTA, starch or other chelate as a retarder, various additives that increase mildew and fire resistance fiberglass or vermiculite, wax emulsion for lower water absorption and water.
CURRENT TEST METHODS
Germany has standardised this sort of testing via DIN Part , dated January , Fire behaviour of building materials and elements, Fire resistance of electrical cable systems, Requirements and testing. Part encompasses both enclosures for cabling and bus ducts, as well as inherently fireresistive cables, such as mineral insulated cables. Enclosures for ductwork as well as wiring are a regular part of passive fire protection there. It is also not nearly as expensive as North American qualified approaches. Typically, lightweight mineral boards are used, such as calcium silicate and sodium silicate bonded vermiculite.The North American state of the art is UL Standard for Tests of Thermal Barrier Systems for Electrical System Components as well as its cousin, UL Standard for Tests of Fire Resistive Cables. UL had its origin with USNRC Generic Letter Supplement , issued by the Nuclear Regulatory Commission. Supplement was to address lessons learned from the widely publicised Thermolag scandal, following disclosures by whistleblower Gerald W. Brown, which resulted on Congressional hearings and a large amount of remedial work.
Supplement is a particularly difficult and expensive test to pass. No testing is done in anything less than a full scale fire test, running easily into figure costs per burn multiplied by all the applications one desires to test. In order to pass, one must test the smallest as well as the largest application and cable tray, and conduit. Accordingly, the approved materials are costly, as manufacturers must get a return on the large test investment.In concept, it is simple to devise systems that will pass the test. As far back as the s, it was apparent that when one uses enough high temperature qualified insulation, such as ceramic fibre, one is assured of a rating. However, this comes at the price of significant ampacity derating. Also, the concept that more fireproofing is better, was defeated by industry tests of Thermolag which is not a fibrous insulation. No matter what was done to this material used for fireproofing purposes over electrical circuits in full scale fire testing by various nuclear power plant owners USNRC licensees who sponsored extensive testing, where more of the old Thermolag was applied onto the older substrate, no satisfactory results were achieved. In order for licensees to come into compliance, other methods, replacements, overlays and MI Cable were used to fix the problem. Also, since the forerunner of this testing was the USNRC, and the commercial version of it UL has undergone various revisions, the UL systems listed in the UL Building Materials directory are not necessarily qualified to the latest USNRC compliant or the latest UL version.
