Firefighters battled a blaze at the telephone exchange in St Neots.
A crew from the town was called to the fire in Tan Yard at 5.16pm yesterday (Sunday), where a high voltage power cable inside the engine room had caught fire.
Wearing breathing apparatus, two firefighters used a hose reel and two CO2 extinguishers to put out the flames. Fans were then used to clear smoke from the building.
Crews returned to base by 8.05pm.
The cause of the fire was accidental.