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Decorative Lighting String by Chia Tsin Electric Co. Ltd. UL Listed Mark: E106094
Furniture, Furnishings & Decorations
Seasonal Decorations
Christmas Tree Lights (1711)
Chia Tsin Electric Co Ltd    
Home Depot
1/2/2018 This date is an estimate
Christmas lights were hung along an unused fireplace hearth and worked for several days. Then the lights quit.

The string was about 50 lamps, each 2.5 volts and 0.425 watts, manufactured by Chia Tsin Electric Co. Ltd. and tagged with the UL Listed Mark E106094.

I found a burned side in one of the bulb sockets. Being a Forensic Engineer, I dissected the socket to determine the cause of the failure. I found one of the brass electrical contacts of the socket seriously bent, making the contact area of one of the wires of bulb a very small point rather than the normal longer contact area.

The socket did not have any external mechanical damage (other than the melted and burned plastic), so the bent contact was definitely a defect in manufacturing.

The point contact the subject contact made a high resistance connection to the wire of the bulb. The heat carbonized the contact which increased the resistance. Normally, an increase in the resistance of a high resistance connection will increase the heat being generated and a thermal runaway would occur, ultimately resulting in arcing. In this case, however, the increased resistance lowered (the already low) current and essentially self-extinguished the process.

The lights were cycled daily, and the melting and subsequent re-solidifying of the plastic may have also helped to interrupt the current. There was no arcing.

I subjected the plastic to a burn test. The plastic burned and melted readily, but self-extinguished upon removal of the flame. The melted plastic would drip while burning, but the drops would also self-extinguish. I can see this could be a problem, however, if the dripping and burning plastic were to land on a present wrapped in tissue paper or other readily ignitable wrapping.

UL has developed a Two Strike program for decorative lighting strings under which UL samples selected strings for evaluation twice each year. Any nonconformance is a Strike, and the manufacturer is not allowed to use the UL Listed Mark until the root cause of the nonconformance is identified and corrected. Two Strikes in a two-year period will result in the termination of its use of the UL Listed Mark. According to UL, Chia Tsin Electric Co Ltd has no Strikes, but its products have not been tested via the Market Survey Program during the past three years.
Incident, No Injury
File NameDescription
IMG_0006.JPG Overview
IMG_0007.JPG Bulb Base
IMG_0008.JPG Socket
IMG_24.JPG Subject contact, bent
IMG_20.JPG Exemplar contact, straight

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