Abstract: An adaptor or connector for use with a continuous outlet current supply installation including a channel-section track member housing elongate conductors, comprises a body portion carrying fixed contact fingers and securing lugs, the whole adaptor being rotatable through 90.degree. to engage the securing lugs with the track and the contact fingers with the conductors, and the adaptor being provided with a switch connected in series with one of the contact fingers and having an operating member in common with a projection which serves to lock the adaptor in proper rotational alignment with the track member, the arrangement being such that the switch cannot be closed when the locking projection is retracted and the locking projection cannot be retracted while the switch is closed.