Effect of relative humidity and materials on triboelectric charging of USB cables

A USB cable can be triboelectrically charged by rubbing it against a piece of clothing, such as a sweater. If a charged cable is inserted into a connector, an ESD event can upset or damage attached equipment. To investigate charge levels and estimate the resulting voltages on a USB cable, a set of experiments has been performed in a climate chamber under five different environmental conditions. These experiments were conducted by rubbing 44 different cables against sweaters made of 100% cotton, 100% polyester, 50% wool/50% nylon, and 50% wool/50% acrylic. The resulting charge levels often reflected the material pairing, as expected from the triboelectric series. The maximum charge level reached -141 nC, or -7 kV, assuming a capacitance of 20 pF between the cable and ground.