When laying armoured cable underground, the cable must be laid at a sufficient depth to avoid the potential for damage or disturbance. If this is not possible, consider increasing the depth of direct burial underground, or providing additional protection for improved security.
Although BS7671 standards do not state a single minimum depth, it's important to ensure that electrical cable will not be disturbed by typical activity. A minimum installation depth of 450mm underground is typically recommended for best practice. This increases to 600mm in locations where there is a higher possibility for potential disturbance.
If installed directly into the ground, the cable should be surrounded by sharp sand to protect against damage to the sheath or insulation. Electrical warning tape should also be in place above the sand to indicate that the cable is present below. On the flip side, if the cable is being installed within a pipe, you must ensure it is watertight to prevent ingress.
It is also important to note that SWA must always be earthed, regardless of whether the armouring is being used as a protective conductor or not. This ensures that automation disconnection of supply (ADS) requirements are fulfilled. The importance of this should not be overlooked, as the development of a fault on a cable that is not effectively earthed could potentially pose a dangerous risk to individuals.
Full, rigorous testing should always be completed post-installation by a qualified electrician. This will ensure that it is both safe and compliant.