Cable Test Chamber
(EN 50399; IEC 603323)
Traditionally electric cables have not been included or classified in national building regulations. The inclusion of electric cables within the Construction Products Regulations (CPR) changes this situation. Cables are to be tested using 5 test methods, and classified by the provisions of EN 135016 which is a parallel standard in the existing CPR classification standard EN 135011. EN 135016 covers electric cable requirements and defines all the test methods and performance criteria that must be met in order for a cable to meet a particular fire classification (Aca, B1ca, B2ca, Cca, Dca and Eca).
According to EN 13501 Part 6: “Classification using data from reaction to fire tests on electric cables”, cables are tested using 5 test methods in which the EN 50399 is the major test protocol for Classes B1ca, B2ca, Cca and Dca. This test protocol was developed by SP (Sweden), ISSeP (Belgium), CESI (Italy) and Interscience (UK) with the help of FTT fire scientists, in an EU funded project called FIPEC, Fire Performance of Electric Cables. The FIPEC project included a study of cable installations and relevant reference scenarios as well as a comprehensive test program of different families of cables. This, together with subsequent industry test programs, was used in the development of the proposal for the European testing and classification system. The classification utilises the results obtained from IEC 603323 test equipment fitted with heat and smoke release measurement instrumentation.
IEC 60332 Series Tests on electric and optical fibre cables under fire conditions
Parts 1 and 2 of IEC 60332 specify methods of test for flame spread characteristics for a single vertical insulated wire or cable. IEC 60332 Part 3 specifies methods of test for the assessment of vertical flame spread of vertically mounted wires or cables, electrical or optical.
FTT IEC 603323 Series Test Apparatus
The test rig comprises of a vertical test chamber of 1000mm (W) × 2000mm (D) × 4000mm (H); the floor of the chamber is raised above ground level. The test chamber is nominally airtight along its sides, air being supplied at the base of the test chamber through an aperture of 800mm × 400mm situated 150mm from the front wall of the test chamber.
The standard requires the air flow rate to be 5000 l/min, measured at the inlet before the test commences. This parameter can be regulated during the test.
An outlet of 300mm × 1000mm is at the rear edge of the top of the test chamber. The back and sides of the test chamber are thermally insulated to give a coefficient of heat transfer of approximately 0.7W/(m2∙K). The distance between the ladder and the rear wall of the chamber is 150mm and between the bottom rung of the ladder and the ground 400mm. Cables can be mounted on two types of ladder; a standard ladder of 500mm width and a wide ladder of 800mm width.
This apparatus also consists of all inlet air and exhaust ducting, gas supply and control system, and two 20.5kW propane burners as specified in the IEC 603323 standard.
EN 50399 Common test methods for cables under fire conditions –
Heat release & smoke production
measurement on cables during flame spread test
IEC 603323 apparatus can be modified to measure heat release and smoke production by fitting a small instrumented section of ducting into the exhaust system of the rig and using this with associated FTT gas analysis instrumentation and software and using a modified test protocol.
The standard specifies the cable mounting methods and both the air inlet duct design and air flow rates into the chamber. The combustion gases are collected in a hood above the test chamber and conveyed through an exhaust system which contains a duct section housing the sampling probes, thermocouples, mass flow probes and smoke measuring system. Test results are calculated from data on continuous measurement of the oxygen consumed and carbon dioxide generated in the combustion process using FTT’s data acquisition and analysis software. The Heat Release and Smoke Production Measurement Apparatus includes:
- Probe & Sensor Duct Section
A stainless steel duct section of approximate dimensions 0.4m diameter by 0.762m long fitted to an exhaust system. The duct will contain ports for:
- Sampling tube for flue gas extraction (for gas analysis)
- Smoke obscuration system
- Mass flow monitoring
- Thermocouple for measuring exhaust gas temperature
- Gas Analysis Instrumentation
Heat release measurement is obtained by sampling combustion products from the exhaust and computing heat release rates from the volume flow rates and the measured oxygen consumption and carbon dioxide generation in the combustion products. Instrumentation is housed in a 19″ rack that can be placed in the laboratory. The 19″ rack cabinet contains:
- Paramagnetic oxygen sensor with flow control and bypass for fast response
- Infrared carbon dioxide sensor (010%) with flow control and bypass for fast response
- carbon monoxide sensor (01%) with flow control and bypass for fast response (Optional)
- Pressure compensation performed in analyser software
Flue gas conditioning train comprising:
- Soot filtration
- Refrigerant cold trap
- Drying columns
- Pump and waste regulators
Instrumentation for volume flow measurement:
- Bidirectional probe
- Differential pressure transducer
Clients already owning the FTT Dual Cone Calorimeter, ISO 9705 Room Corner Test or EN 13823 SBI Test can use their gas analysis instrumentation to measure heat release rate of the EN 50399 test. Alternatively the EN 50399 gas analysis instrumentation can be used with other FTT calorimeters (e.g. Dual Cone Calorimeter, ISO 9705, SBI, etc.).
- Smoke Measurement Systems FTT offers two smoke measurement system options, laser or white light systems. The laser system is similar to that used in the Cone Calorimeter and complies with that specified in ISO 5660. The white light system is similar to that used in the SBI test and constructed to DIN 50055.
- Density Photometric System DIN 50055
- A photometric system consisting of a white light source and lens, a silicon photodiode detector, along with housings and controls. The photodiode detector consists of an achromatic system of lenses, a silicon photoelectric cell and a high gain low noise amplifier. The latter is capable of measuring relative light intensity against time as percentage transmission continuously over the ranges to be studied. The system has a linear response with respect to transmission and an accuracy of better than ±1.5% of the maximum reading. The photodiode is housed in an assembly with a collimating lens, in a tube mounting on the side of the exhaust duct.
- Laser Smoke System
- As an alternative to the DIN 50055 system, a laser smoke system can be used. It features a 0.5mW Helium Neon laser smoke and support system, power supplies, calibration and zeroing device for smoke extinction coefficient. The detector output is designed with a Main and Compensating Detector to eliminate drift and is supplied with 0.3 and 0.8 neutral density filters for calibrating the unit. Calibration and calculation of the associated smoke obscuration parameters can be performed by FTT software.
- Data Acquisition & Analysis Software
The signals are collected using a Data Acquisition Unit. A Windows based software package enables data acquisition and analysis to determine the various parameters needed for heat release determination.
- Burner Gas Control Unit The system supplied comprises of a gas flow control and ignition system for the burner. A spark igniter is provided and a typeK thermocouple monitors the presence of a flame. Two mass flow controllers (MFCs) control the propane gas and air flow and a Venturi air gas mixer. Each MFC is housed on the ‘Gas Diverter’ plate fitted on the outside wall of the test chamber. This is normally protected behind a cover. The Gas Control Box enables each gas to have 3 preset levels. After presetting, the burner output can be switched between these levels. It also houses the numerous power supply units for the MFCs and solenoid valves, the ignition system and controls for the safety features. The signals from the MFCs are displayed on screen using FTT CableSoft software, which shows the mass flow rate of the respective gas and the corresponding heat output and facilitates any required adjustment. The mass flow rate of each gas is also stored by the software enabling heat release from the burner to be subtracted from the total measured heat release rate (of specimen and burner) so that the heat release rate from the specimen alone can be determined.