Why cable cleats are vitally important in the protection of a cable installation

Summary form only given. Amongst the plethora of theory, standards and literature regarding fault protection, and arguably amongst the immediate understanding of the term ´fault protection´, very little attention is given to a crucial piece of equipment in a power cable installation the cable cleat. Very often attention is given to other ´cable accessories´ such as joints, glands and terminations, but often the cable cleat is overlooked and left until the end of the installation process where it is included in the ´bulk´ call off for consumables or general fittings. Most engineers recognise the importance of topics such as circuit design and layout, fuses, circuit breakers and the like, and these issues are undoubtedly essential. However, the engineer often overlooks the fact that the timing of an ´typical´ breaker is approximately 3-5 cycles, or 0.06 0.1 seconds on a 50 Hz system (an exceptionally quick relay may operate at 1.5 cycles). However, if one considers a phase to phase fault, and we look at the highest and most destructive forces i.e. at the peak of the fault, we need to consider a time point of a quarter of a cycle i.e. 0.005 seconds. The intention of this paper is to underline the necessity of providing a cleating solution which ensures that the electro-mechanical forces are restrained and the power cables remain in position for long enough to allow circuit breakers to act and arrest the fault. A comprehensive description of the testing which is necessary to conform to the appropriate legislation will be given. Discussion will focus on different types of power cable construction and various fault levels. Preliminary in-house testing will be discussed and also specialised ´live´ short circuit testing which is carried out in the Netherlands. The paper includes photographs taken from these tests which demons