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More power, faster: A look at charging cable safety issues

Do you know how to verify the safety of your USB charging cables? One of UL’s Wire & Cable experts offers insights on powered technology, its evolution and challenges, and how UL supports safety testing and certification.

laptop and mobile phone with charging cables

October 21, 2019

Since the 1990s, cables and connectors have facilitated the connection of many types of information and communication technology (ICT) equipment such as smart phones, keyboards and disk drives. Today’s technologies have brought power delivery to new levels, with a demand for faster charging and the powering of higher powered devices.

Users are not typically aware of the potential risks of overheating and fire associated with these higher power levels. The power required to charge and operate today’s devices has led to a rise in reports of smoke, fire or damage to connected devices. We talked with UL’s Randy Ivans, program/project manager in the Wire & Cable Division, for some insights.

Q: How has powering technologies evolved in recent years?

A: Universal serial bus (USB) is the most popular low-voltage powering scheme in use today. In the USB 1.0 and 2.0 specifications, a standard downstream port could deliver up to 500 milliamps (0.5 amperes).

Today, the power delivery specification over USB connector permits voltages as high as 20 volts and currents up to 5.0 amperes (100 watts). This can supply enough power to soldering irons used in the electronics which are mostly in a range of 20 – 60 W.

Q: Does this power increase raise any safety concerns?

A: Yes it does. As powering technology has evolved, the widespread use of the various connectors, including some nonstandard applications, has presented its own set of challenges. Users encounter problems with devices and cables that don’t comply with industry specifications. These problems include slow charging rates, devices which fail to function as intended and damage that could lead to the increased risk of fire.

In reality, many electronics manufacturers choose to not strictly adhere to the operational limits identified in the specifications, and may go beyond the operational limit to offer the maximum current.  Inexpensive or poorly designed power and charging cables and connectors can pose a potential safety risk to users and have even resulted in damage to or the destruction of some connected ICT devices.

Q: Do you have any examples?

A: In a report posted to the CNET website in early 2016, two technology professionals reported that their laptop computers were severely damaged when they plugged in USB-CTM-to-USB-A adapters they had purchased online. In both cases, a resistor used in the adapters did not meet applicable USB Implementers Forum (USB-IF) specifications. One of the two professionals went on to evaluate over 100 different adapters available online, and more than half of them failed to meet the applicable USB specifications.

Additionally, UL conducted cable flame tests on a random set of USB cables purchased on the open market. Less than 28% of the cables tested passed the flame test, and many of the tested samples were completely consumed by fire.

Q: What are some ways to mitigate the risks?

A: The most basic way is to comply with industry specifications. All industry specifications relating to power delivery outline requirements that limit the amount of current, minimizing the risk of fire and overheating.

Q: How does UL address potential safety concerns?

A: UL has prepared UL 9990, Outline of Investigation for Information and Communications Technology (ICT) Power Cables. The criteria in UL 9990 have been developed to complement the existing industry performance specifications, and together they provide a comprehensive evaluation of both the performance and safety characteristics of powering cables.

We went on to integrate UL 9990 into a comprehensive safety certification program for ICT power and charging cable assemblies.

To learn more about powering cable safety issues and UL’s research and response, read our white paper: “Powering and Charging Safety for Data Sync and Charger Cables."


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