Abstract: A fuse holder (20) is provided that can be installed in the place of a dropout fuse element in an electrical insulating unit (1). The fuse holder has an elongate electrically insulating body providing at least one electrically insulated elongate fuse housing in the form of a passage (21) associated with the body and adapted to receive a fuse wire (22) held under tension therein. The body can be installed in such insulating unit as a replacement to an existing dropout fuse element (5) and itself provides contacts enabling such a conventional dropout fuse element to be installed in the fuse holder body from which it can drop out when the fuse is blown. A switch arrangement is provided for maintaining a fuse in the passage in an inoperative condition whilst a dropout fuse element is functional and for automatically closing an electrical circuit through a fuse installed in said passage when the dropout fuse becomes blown and drops out of the fuse holder.