Application guide 05 / 12
Underground Cable Bedding & Backfill
A buried power cable is only as good as the material around it. Thermal bedding sand packs tightly and carries heat away from the cable.
Our products: Thermal Bedding Sands · Select Fill
MRP thermal bedding sand for cable trenches
MRP supplies thermal bedding sand for underground power cables across Queensland. A cable carrying current makes heat. If the heat cannot escape, the cable runs hot and has to be derated — run below its design current — or it fails early. The material around the cable is the path the heat takes into the ground. Air blocks heat, so the fewer air voids in the backfill, the lower its thermal resistivity and the more current the cable can safely carry.
What we have to get right
Density. A well-graded sand, with its full range of particle sizes including the fines, packs into a tight mass with few voids when it is compacted around the cable. A washed, single-sized sand does the opposite: it leaves voids, and voids are air. That is why thermal bedding sand is not washed. The fines that washing would strip out are what let it compact.
The MRP product
Thermal Bedding Sand is screened and graded to keep its fines and pack densely. It is supplied for cables in trench, at substations and on renewable energy grid connections. Where a project also needs engineered fill for platforms and access, Select Fill is supplied with it.
Supply
Bulk supply to electrical contractors, civil contractors and utilities across Queensland, scheduled to the trenching program. Tell us the project, the specification or thermal resistivity requirement, the tonnage and the site.