Skill: Cable Size for Gate Power Runs
Skill level: 3
Wiring
Learning Objective:
Understand how to determine the appropriate size of SWA cable based on current draw, voltage drop, installation method, and length of run — specifically for typical 230V gate automation systems.
1. Overview
Gate automation power runs are typically light loads (<6A), but design must allow for future accessories and occasional 13A socket loads. Correct cable size avoids excessive voltage drop, overheating, and non-compliance with UK wiring regs.
2. Tools & Materials
Cable size reference table or calculator
Measuring wheel/tape (for accurate run length)
Multimeter (for end-to-end continuity and insulation check)
2-core or 3-core SWA cable (default choice)
Correct glands, cleats, and termination tools
Access to certification method
3. Typical Loads to Supply
Gate control board linked to motors
Intercoms
Optional socket for service tools
Garden lights
Most installations: <6A continuous load. Gate control boards are fitted with 3A -6.3A fuses so feed must be equal or more.
Worst-case: 13A spur if socket or power tools are added.
Occasionally customers will want to future proof to the extent of putting a new shed or garage by the gates. In this case a much larger supply would be needed, potentially 40A. This being the case a separate enclusure would be a better location for a new feed, then take the smaller gate feed from that.
4. Procedure
4.A common cable types
3-core SWA (Steel Wired Armoured) 2.5mm, 4mm or 6mm CSA (cross sectional area)
PVC insulation, 70°C rating
Installed either:
Buried (direct in trench, usually with sand/duct)
Surface clipped to walls or fences
No grouping or high ambient derating normally applies in gate jobs. That is to say that inside buildings or where power cables run close to each other the heat they generate must be considered as it affects the conductivity of the cable. This is not usually relevant to gate systems supplies.
4.B Rule of Thumb for Gate Jobs
Run Length -------- Cable Size -------- Notes
Up to 50m -------- 1.5mm² -------- Safe for gates only (~6A). Not for 13A socket use.
Up to 100m -------- 2.5mm² -------- Preferred default — covers gates + 13A socket.
Up to 200m -------- 4.0mm² -------- Rare. Confirm with qualified electrician.
✅ Use 2.5mm² as standard up to 100m for reliability and future-proofing. This will allow for lighting and a single 13A socket although we do not advise fitting sockets to gate control boxes as it does nothing for safety and reliability.
4.C Voltage Drop Considerations
Voltage drop occures when electricity has to run through cables, the longer and thinner the cable and the more power is required the more the voltage drops. Voltage drop causes lack of power to the appliance or light being fed. The max legal voltage drop in the uk is 5% for lighting circuits and 3% for all other circuits.
Lights are affected more by voltage drop and flurescents may not light up at all if the voltage is too low.
UK regs: Max 5% VD (≈11.5V at 230V).
Quick Reference (SWA clipped direct, 70°C PVC insulation):
Cable Size -------- Max Amps -------- Max Run @ 6A -------- Max Run @ 13A
1.5mm² ---------------- ~16A ---------------- ~90m ---------------- ~35m
2.5mm² ---------------- ~21A ---------------- ~150m ---------------- ~60m
4.0mm² ---------------- ~28A ---------------- 200m+ ---------------- 100m+ OK
⚠️ If adding a socket or higher-load accessory, never rely on 2.5mm² beyond ~60m, you'd have to step up to 4mm cable
4.D Earthing
Opinion varies on earthing for gate motors, some say use TT earthing, others are happy to earth back to the fuseboard. Regs state metallic equipment located outdoors (e.g. gates, fences, external pipework, lighting columns, EV chargers, etc.) could introduce a potential from earth and therefore special earthing arrangements (often TT) are required. TT earthing uses an earth stake and an RCD at the gate end.
However, when using 24v gate motors the motor and accessory power is extra low voltage and is double insulated, so the feed only controls the control board's transformer which does not even have an earth tab. So TT earthing is impractical. In this case you can connect the earth and the sheething to the body of the spur which will protect the cable incoming to the system.
4.E 2-3 core?
The science and regs is a bit beyond the scope of this lesson. Technically 2 core can be used sometimes and the wire armour used as an earth but to keep things simple and cover every eventuality use 3 core.
7. Best Practices
✅ Default to 2.5mm² 3 core SWA for anything up to 100m, no sockets over 60m
✅ Terminate SWA with correct glands (banjos and earth continuity).
✅ Label cable ends (gate supply, length, date).
✅ Get the feed signed off by a qualified person.
✅ Photograph trench, duct, and terminations for Clik.
8. Common Mistakes to Avoid
🚫 Undersizing cable → high VD, unreliable equipment.
🚫 Using T&E cable outdoors or underground.
🚫 Forgetting about possible socket addition.
🚫 Mis-measuring run length (always measure actual route, not straight line).
🚫 Ignoring future-proofing — saves little but causes big problems later.
9. Safety Information
Relevant SSOW References:
SSOW-01: Electrical Isolation & Lock-off
SSOW-02: Underground Cable Installation (Trenching & Ducting)
SSOW-05: Safe Use of Multimeters
SSOW-09: SWA Termination & Earthing
SSOW-11: PPE (gloves, boots, eye protection when trenching/cutting)
⚠️ Only qualified electricians should make final terminations into consumer units.
⚠️ Always test insulation resistance and continuity before energising.
⚠️ Confirm correct earthing and bonding of SWA armour.
