Nidec shares plunge 18% on report of $6.3 billion impairment

Nidec, the Japanese maker of electric motors, saw its shares slump 18% after a report disclosed a $6.3 billion impairment charge. The size of the writedown caught investors off guard and triggered one of the steepest single-day drops for the company in recent memory. Impairments of this scale typically signal that a business unit or acquisition has lost much of the value it was originally booked at, forcing a company to admit the asset is worth far less on paper. For Nidec, a company whose motors go into everything from electric vehicles to data-center cooling systems, a charge this large raises questions about which part of its portfolio has underperformed and why it wasn't flagged earlier. What remains unresolved is which specific business line or acquisition triggered the charge, and whether Nidec's guidance for the current fiscal year will be revised downward when it next reports results.