Underground Cable
Depth of cover and separation for a buried cable.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
What does the underground cable tool do?
The tool reads the wiring system category for your cable type and method of protection. It then reports the minimum depth of cover for the location and surface covering, the bedding depth, the marker tape depth and the separation from another underground service.
Which tables does the result come from?
The category comes from AS/NZS 3000:2018 Table 3.5. The depth of cover comes from Table 3.6. The separation comes from Table 3.7. Bedding, mechanical protection and marker tape depth come from Clauses 3.11.4.2, 3.11.4.3 and 3.11.4.5.
How deep must a buried cable be in New Zealand?
It depends on the category and the surface. A Category A or B system elsewhere than a building needs 500 mm of cover with no concrete above, or 300 mm under poured concrete of at least 75 mm. A Category C system needs 50 mm.
What does Category B mean for the trench?
Category B needs additional mechanical protection above the cable. The tool reports the rule: not more than 75 mm above the wiring system, at least 150 mm wide, and at least 40 mm of overlap on each side. Bedding is 50 mm of sand or friable soil.
Why is a combination marked as not permitted?
Table 3.5 marks some cable and enclosure pairs NP. An example is unsheathed conductors buried direct in the ground. The tool reports the combination as a fail and gives no depth. Choose another enclosure or another cable type.