Emergency services were called out after a smell of burning was reported in an East Grinstead office on Saturday (April 12).
Firefighters went to the building in High Street, East Grinstead, at around 4am.
A search was made using a thermal imaging camera and a small fire was found in an electrical fuse box.
It was put out by isolating the electrical supply.
A further inspection was then made using the thermal imaging camera.