The rapid increase in the power required to charge and power mobile devices including laptop computers, tablets, mobile phones and power banks, has led to increasing reports of damage, smoke, or fire with these connected devices; sometimes this damage is caused by poorly designed or faulty cables. In addition, these higher power levels can put the cable assembly itself at risk if the cables are used to power or charge devices in excess of their power handling capacity or if fault currents exceed these capacities. While legacy systems have been able to deliver up to 1.5 amperes at 5 volts to power and charge devices, power levels are rising to meet the demand for faster charging and the powering of higher-powered devices. The power delivery sources using the new USB Type-C connector can deliver voltages as high as 20 volts and currents up to 5 amperes. That’s 100 watts, enough to power a soldering iron!
These improvements are necessary, but users may not be aware of the potential risks of overheating and fire due to the use of poorly constructed cables. Improperly terminated connectors, the use of substandard materials and cables and the incorrect use of electronic markers intended to help match source and load currents all add to the growing risks associated with these cable assemblies. To address the potential safety risks, UL developed an Information and Communication Technology (ICT) Power Cable certification program specifically for cable assemblies that provide data transmission and power or charging for connected equipment in a low voltage, limited energy circuit that does not exceed 60 V dc, 8.0 A and 100 W. UL’s program addresses safety concerns by subjecting the cable assemblies to a series of rigorous mechanical and electrical tests and through the control of connector/cable materials. These requirements were recently published in UL 9990, Outline of Investigation for Information and Communication Technology (ICT) Power Cables.
In addition to routine continuity tests to check cable assembly, cables are subjected to strain relief and flexing tests that simulate excessive “normal” use. Connections and stress relief means shall not be damaged during these tests. Dielectric-voltage withstand tests check that adequate electrical spacing is provided and temperature testing at the rated full load current ensures the cable and connectors will not overheat. A fault current test demonstrates that the cable assembly itself will not become a risk of fire to surrounding materials if subjected to abnormal overload current. Finally, the cable is checked for proper use and operation of electronic markers (if used) with respect to the electrical ratings and connector configurations used. This eliminates “cheater cables” that are intentionally designed to mislead the source or load circuits to provide excessive power or charging currents that can damage powering or powered devices and present a safety hazard.
We’ve all read reports or have seen pictures depicting cell phones that have overheated or caught fire. Although, as stated earlier, some of these incidents can be traced to “cheater” cables overpowering the battery charging circuits, there are times when the events can be traced to questionable designs, manufacturing defects or counterfeit products. This applies not only to the load device, such as a phone, but also to the charger itself where cheap construction can result in the power supply overheating and possibly igniting, presenting an extreme risk of fire. In this scenario, the question then becomes whether or not the fire will be localized or propagate to potentially flammable materials such as papers on a desk, upholstery or bedding.
UL 9990 includes requirements for both the connector materials and cable flame propagation that are intended to limit fuel contribution and the spread of fire. Connectors are required to be constructed of materials with a minimum flame rating of V-1 or comply with the criteria for SC-1 in accordance with UL1694, Standard for Tests for Flammability of Small Polymeric Component Materials, for parts with a volume of 2500mm3 or less, or with the 12 mm flammability criteria end-product flame test described in accordance with UL 746C, Standard for Polymeric Materials – Use in Electrical Equipment Evaluations.
Cables are required to comply with VW-1 criteria that require the cable to be self-extinguishing after two flame applications and produce minimal flaming drip. This requirement also applies to cables with decorative coverings such as fancy braiding or faux leather where the combination of cable with covering is tested.
UL certifies these cable assemblies under the category for Information and Communication Technology (ICT) Power Cables (NWGI). To align with the latest industry standards, this category requires USB Type C cable assemblies to be certified by the USB Industry Forum (USB-IF) before being eligible for UL safety certification. For USB Type C cable assemblies that are not certifiable by the USB-IF, such as those that have a proprietary (non-USB) connector on one end, the USB Type C connector must be certified by the USB-IF.
The game changed when the use of ICT cable assemblies shifted from simply transmitting data and powering very low powered devices like keyboards to the main power source for increasingly power hungry mobile devices. UL is meeting the resulting challenges with the introduction of this new certification category and outline of investigation to continue its mission of “Working for a Safer World.”