What the Latest Wiring Regulations Update Means for Armoured Cables

Overview of BS 7671 Amendment 4

Amendment 4 to BS 7671:2018 has now been published, updating the UK Wiring Regulations and providing greater clarity in several areas that directly affect cable selection and performance. While BS 7671 governs the safety of electrical installations, one of the most significant changes in Amendment 4 sits squarely in the domain of cables and wiring systems and more specifically, how armoured cables installed underground are rated depending on how they are buried.

As a global designer and manufacturer of energy and data cables, Prysmian focuses on how Wiring Regulations changes translate into measurable cable performance requirements, and how the Prysmian CableApp can support installation decisions. Amendment 4 continues the evolution of BS 7671, improving it’s clarity and consistency whilst closer aligning it with wider European practice and maintaining a strong focus on demonstrable compliance.

BS 7671 Amendment 4 Explained: What’s Changed and Why It Matters

Amendment 4 is an update to the 18th Edition of BS 7671 rather than a wholesale rewrite. Its purpose is to refine existing requirements, remove ambiguity and ensure that the Wiring Regulations reflect modern construction methods, materials and installation environments.

The amendment has now been published, with a defined transition period during which previous amendments may continue to be used where permitted. As with earlier editions, designers and specifiers should clearly state the edition and amendment of BS 7671 applied to each project and ensure that cable data, calculation tools and specifications are aligned accordingly.

Buried vs Ducted Armoured Cables: How Amendment 4 Changes Current‑Carrying Capacity

One of the most important cable‑related updates in Amendment 4 concerns current‑carrying capacity for armoured cables installed underground. Prior to this amendment, armoured cables buried directly in the ground and armoured cables installed in ducts in the ground were often treated using a single set of underground rating assumptions.

Amendment 4 addresses this by clearly distinguishing between these two installation conditions, recognising that the thermal environment for a cable buried directly in soil is different from that of the same cable installed within a duct. The presence of a duct can restrict heat dissipation and therefore affects the cable’s allowable current‑carrying capacity.

By separating these scenarios, Amendment 4 improves the technical accuracy of cable ratings and reduces the risk of over‑ or under‑sizing cables based on overly generalised assumptions. For armoured cables, this brings cable ratings into closer alignment with how they actually perform in service and reinforces the importance of selecting the correct installation method during the design stage.

Other cable‑relevant clarifications

Alongside underground ratings, Amendment 4 also strengthens cross‑references around reaction‑to‑fire classifications for cables where required, supporting clearer specification in applications such as escape routes and shared service spaces. This reinforces the distinction between reaction‑to‑fire performance and other aspects of cable behaviour, helping ensure that cables are selected based on declared, test‑based performance.

Additional refinements to current‑carrying capacity factors, grouping, ambient conditions and installation methods further emphasise the need for accurate cable data and disciplined application of correction factors, particularly in complex or thermally challenging environments.

Applying Amendment 4 with Prysmian CableApp

To help the industry apply these changes consistently, Prysmian CableApp has been updated in line with BS 7671:2018 Amendment 4. The cable calculator incorporates the revised treatment of armoured cables installed underground, enabling users to differentiate correctly between direct‑buried and ducted installations when determining current‑carrying capacity.

As an armoured cable calculation tool developed by an armoured cable manufacturer, CableApp is built on validated Prysmian cable data and aligned with the latest Wiring Regulations. It supports accurate selection of conductor size, voltage drop and fault performance based on declared cable characteristics and defined installation conditions.

By combining deep expertise in cable design and manufacture with a practical digital tool, Prysmian helps designers and specifiers translate Wiring Regulations updates into robust, evidence‑based cable choices. Amendment 4’s clarification on buried and ducted armoured cable ratings is a clear example of how improved regulation, supported by accurate cable data, leads to better‑engineered electrical infrastructure.