SWA Cable Installation Guide
SWA cable installation is a design task as well as a glanding task: current capacity, voltage drop, mechanical protection and earthing all matter.
Steel-wire-armoured cable is often used for sub-mains and external runs because it provides mechanical protection. Select it from the load, route, installation method, environmental exposure and required protective-conductor arrangement — not simply from the previous job.
This is practical guidance for competent electricians. Assess the actual installation, follow the current edition of BS 7671 and manufacturer instructions, and stop where the work cannot be completed safely.
Key takeaways
- Agree the scope and make the installation safe before starting work.
- Use a controlled sequence rather than relying on a single reading or visual assumption.
- Record the actual result, limitation or action taken while it is still traceable.
- Check the result against the design, protective measures and equipment instructions.
- Issue the appropriate certificate or report when the work is complete.
Scope the work first
Steel-wire-armoured cable is often used for sub-mains and external runs because it provides mechanical protection. Select it from the load, route, installation method, environmental exposure and required protective-conductor arrangement — not simply from the previous job.
Method
Plan the route, support or bury the cable appropriately, use compatible glands and earth tags, make off the armour correctly and protect the terminations from water ingress and mechanical strain. Test the completed circuit before energisation.
Doing this on a job? Cable sizing calculator — part of TradePlanr. Free to start, no card needed.
Checks and common pitfalls
Common failures include poor gland preparation, damaged bedding, inadequate support, unprotected entries and an assumed rather than verified armour earth path. Long runs frequently fail voltage-drop limits before they fail current capacity.
Record and hand over
Record the cable type, size, route, protective device and test values in the certificate. Photograph inaccessible routes and label isolation points so future work can be completed safely.
Keep the evidence with the job
Record readings, limitations and remedial actions as you work. A clear certificate or report protects the client and makes the next visit easier to manage.
From guidance to action
Frequently asked questions
Can the SWA armour always be used as the CPC?
The protective-conductor arrangement must be designed and verified for the installation. Do not assume the armour alone is adequate without considering the cable construction, fault path and applicable requirements.
Can I rely on a standard rule of thumb?
No. The installation method, supply characteristics, equipment instructions and the current requirements all affect the correct decision. Use the guide as a workflow, then assess the actual job.
What should be recorded?
Record the scope, results, limitations, observations, remedial work and the certificate or report appropriate to the work carried out.
Related guides
Garden Office Electrics: Supply and Wiring
Design a garden office sub-main: SWA sizing for voltage drop, burial, a consumer unit and PME earthing pitfalls.
Cable Reference Methods Explained
How cable installation reference methods affect current-carrying capacity, correction factors and final cable selection.
Cable Sizing to BS 7671
The full cable sizing method — design current, correction factors, tabulated ratings and volt drop.
