Contact voltage losses

Contact voltage losses occur due to defects in low voltage cables, caused through aging, chemical corrosion or third party damage. These defects result in the energisation of the metallic cable sheaths with consequent losses through heating.

The loss associated with this earth fault leakage is called a Contact Voltage Loss, because the fault is detectable on the surface by detecting ‘contact voltage’. The Mobile Asset Assessment Vehicle (MAAV) detects these voltage changes and locates the precise area where we have to dig to find the defective cable.

The MAAV drives around urban areas at night at about 25 mph. Its sensitive electromagnetic sensors pick up the signatures of contact voltages and when detected, an operatives undertakes analysis to find the precise location of the fault. This might be buried under a pavement or inside a piece of street furniture. This is then marked and UK Power Networks engineers are alerted to come and repair the defect.

Contact voltage loss magnitudes are considerable, but typically masked by existing load as they are not significant enough on their own to operate protective devices. Princeton University calculate that the total amount of losses attributable to CVL are 590 GWh per year in the whole of Great Britain.