The connection and termination of electrical cables has to be done with utmost care. A bad connection can lead to short circuits. When it comes to the termination of MV and LV cables, shear head lugs are widely employed. Here under, we detail you a few technical aspects of these connectors.
Principle of shear head connectors:
Shear head lugs and bolts have emerged as a best solution to connect the electrical cables. Over the years, vast changes have taken place in their manufacturing and designing methods. Of late, multiple shear off bolts are being introduced and they are gaining popularity over the orthodox types. The time involved in the installation process is greatly reduced by these connectors. The working principle of these bolts is detailed here under:
· The dimensions of inner and outer hexagon are distinct and each of it is designed to have a distinct shear off area. Thereby it is to be understood that each of it has a unique working torque limits.
· If the cross sectional area of the conductor is large, it requires intense torque moments to terminate it. The required torque to be applied is directly proportional to the area of the cross section.
In most general applications, the bolts are designed only to withstand the frictional force which develops at the contact surface. However, the regular connectors and bolts can be of no use when the system generates too much shear force. To meet such situations shear bolts are designed. In this case, the excess shear force gets absorbed by these bolts and the anchor bolts can function effectively. The base plate which is welded at the bottom portion of the lug absorbs the shear force. The design has to be so made that it the connector is least affected by the contact frictional forces. The design procedure adopted for these connectors is detailed below:
· The most important factor in designing a shear lug is getting to know the shear load applied across this connector. This load varies with the type and cross section of the connector.
· Shear lug plate is the only part of the connector which is responsible in the transfer of shear forces. As we could determine then maximum load applied on it, a corresponding bearing area to withstand this load is calculated.
· It is assumed that the bearing takes place only at the base of the lug and the dimensions are determined. The height of the lug, thickness and size of the base plate can be known.
· After estimating the desired dimensions of the lug, the designer should focus on the moment caused due to cantilever forces. This force enables us to know the optimum thickness of the lug. One has to take care that this thickness doesn’t exceed the thickness of the plate.
The above detailed design procedure is a generalized method and there are good chances that this procedure can vary from different applications. Before purchasing a shear lug get to know the design standards and the manufacturing methods followed by the manufacture. If at all you have to employ a few accessories to the system make sure to purchase them from the same manufacturer.