Original vintage industrial electrical safety sign, warning that the apparatus can be energised through a tee feeder and must be isolated at the remote end before work is carried out. This is a classic British enamelled metal “DANGER” sign, intended for use in electrical switchgear rooms, substations, factories, power stations, dockyards, or large municipal buildings. The wording reflects older electrical distribution systems where multiple feeds could remain live, making this an important and historically interesting safety notice. A genuine piece of early-mid 20th century industrial history, not a reproduction.