South Korean electric wire and cable manufacturer Taihan Cable & Solution has faced challenges of quality control after using impure copper from a new supplier in its production process, industry sources said Wednesday.

For approximately three weeks -- from early last month to Sept. 24 -- the company’s Dangjin plant in South Chungcheong Province had shut down its copper rod manufacturing. Copper rods are a basic metal element in cable production.

The melting furnace was reportedly clogged due to a low-purity electrolytic copper cathode that was inserted in the equipment to test its quality before forging an official partnership. Copper rods require high-purity copper cathodes -- more than 99.99 percent purity -- but the material evidently contained foreign matter.

Taihan Cable said it had unintentionally used the poor-quality copper produced from a new supplier as part of its strategy to diversify its supply chain after the COVID-19 pandemic. Details on the supplier were not made available.

After fixing the equipment, the company resumed its manufacturing process from Sept. 26 and the supply of copper rods to its partner companies the next day.

While the company claims the incident resulted from efforts to diversify its supply chain, industry insiders suspect it was caused by the company’s cost-reduction strategy.

“The company seems to have tried to reduce the cost (of electrolytic copper cathodes) by working with an unverified supplier. It might take some time for Taihan Cable to start producing high-quality copper rods,” an industry source said on condition of anonymity.

An official from Taihan Cable & Solution rebutted the claim, saying, “Our plant has already restored the quality of the product. There could be no quality issue because we not only sell the copper products (to other companies), but use them ourselves to make cables.”

During the shutdown period, Taihan Cable imported some 300 tons of copper rods from a China-based company as a backup plan to supply to partner firms.

“Contrary to concerns on the quality of the China-made products, we are sure there was no such issue based on our thorough inspection,” the official said. “Other partner companies also had vouched for the high-grade copper.”

Taihan Cable & Solution’s Dangjin plant manufactures copper rods and superconducting cables with 29,220 tons of annual production capacity. As of last year, its copper rods and winding business accounted for 50.36 percent of its total 2.45 trillion won ($1.8 billion) in sales.