SHEFFIELD — Nearly 4,500 National Grid customers in the Southern Berkshires were briefly in the dark Tuesday evening.

Utility officials say at 6 p.m. a supply line for the electric company malfunctioned in Sheffield causing an outage that affected Sheffield, Great Barrington and Stockbridge.

Within 10 minutes the utility isolated the problem and had power restored. What caused the main line to go down was not immediately known.