Testing and application of crushed aggregate for use as a resistive substation surface layer

For the purposes of IEEE Std 80 and touch and step voltage analysis in substation grounding system design, the primary role of substation surface material is to increase series resistance to thereby limit current through the human body. Therefore, with a surface layer of high resistivity material installed higher touch voltages may be permitted and still present the same risk to personnel as lower voltages with no crushed rock. This technical report discusses the factors that impact the electrical resistivity of a crushed aggregate layer, test methods in use, and recommends methods that may be used to test a sample of aggregate in a laboratory as well as in the field. This report aims to provide asset owners and designers with confidence when designing and installing a grounding system to comply with tolerable shock safety targets. This report also provides appropriate specification, installation, and commissioning procedures, as well as ongoing inspection and maintenance procedures that can detect non-conformances.