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Plastic Cable Conduit Guide: PVC Sizes, Gauges and Fittings
Updated October 2026 · Meteor Electrical guides · 9 min read
Quick answer: Plastic cable conduit is a PVC tube that protects and routes electrical cables. Use rigid PVC conduit for neat surface runs and flexible conduit for final connections. 20mm and 25mm are the most common sizes, heavy gauge suits most exposed work, and black UV-stabilised conduit is the usual outdoor choice. PVC is not an earth, so always run a separate cpc.
This is our buying guide to plastic cable conduit, also called PVC conduit. It covers the choices that matter when you order: rigid or flexible, which size, light or heavy gauge, white or black, the fittings you need, bending springs, LSF conduit and outdoor use. For a wider look at every conduit material, see our guide to the types of cable conduit, and for step-by-step fitting, our conduit installation guide.
In this guide
- What is plastic cable conduit?
- Rigid or flexible PVC conduit?
- Which size: 20mm, 25mm or 32mm?
- Light or heavy gauge?
- White or black PVC conduit?
- Which PVC conduit fittings do you need?
- How do bending springs work?
- What is LSF / LSZH conduit?
- Can plastic conduit be used outdoors?
- Plastic or steel conduit?
- FAQs
What is plastic cable conduit?
Plastic cable conduit is a tube, usually made from PVC (polyvinyl chloride), that encloses electrical cables. It protects them from knocks, abrasion and moisture, keeps runs neat, and lets you pull cables in or out later without disturbing the building.
In the UK and Ireland it is most often used for:
- Surface wiring in garages, workshops, outbuildings, plant rooms and commercial units where cables cannot be hidden in walls.
- Single insulated cables (such as 6491X / H07V-U). BS 7671 requires non-sheathed cables to be enclosed in conduit, trunking or ducting, so conduit is essential when you use them.
- Protecting twin and earth where it is run on the surface or where it could be damaged.
- Damp and corrosive places such as farm buildings and coastal sites, where steel would rust.
Conduit is made to the BS EN 61386 series of standards, which classify conduit by strength, temperature range and other properties. Check the markings and datasheet so the product suits where it will be installed.
Rigid or flexible PVC conduit?
There is no single best plastic conduit. The right choice depends on the route, the environment and how much protection the cables need.
| Type | What it is | Best for |
|---|---|---|
| Rigid PVC conduit | Straight 3m lengths of round PVC tube, joined with couplers and circular boxes | Neat surface runs on walls and ceilings, garages, workshops, plant rooms |
| Flexible PVC conduit | Corrugated or spiral PVC tube that bends by hand, used with glands or adaptors | Final connections to motors and equipment, awkward routes, short outdoor drops |
| Oval PVC conduit | Low-profile oval tube that sits flat under plaster | Protecting cable drops chased into walls to switches and sockets |
| LSF / LSZH conduit | Rigid conduit made from low smoke, zero halogen material | Escape routes, public buildings and anywhere smoke and fumes are a concern |
Most jobs use both: rigid PVC conduit for the main run, and a short length of flexible conduit for the final connection to a motor, pump or piece of equipment that vibrates or needs to move. Flexible conduit such as 32mm black flexible PVC conduit is also handy where a rigid route would need lots of bends. For the full range of flexible options, see our guide to flexible cable conduit.
Video: flexible conduit systems for faster installations. Credit: eFIXX on YouTube.
Which size: 20mm, 25mm or 32mm?
PVC conduit is sold by its outside diameter in millimetres, usually in 3m lengths. Sizes run from 16mm up to 50mm, but three sizes cover most work:
| Size | Typical use | Notes |
|---|---|---|
| 20mm | Domestic lighting and socket runs, single cables to switches and accessories | The most common size; boxes, saddles and springs are widely stocked |
| 25mm | Busier runs with more cables, larger cable sizes, garage and outbuilding supplies | A sensible default when you may add circuits later |
| 32mm | Submains, larger cable groups and longer pulls | Larger bending radius; often paired with flexible 32mm for final drops |
Do not size conduit by eye. Overfilled conduit makes cables hard to pull, damages insulation and traps heat. The IET On-Site Guide gives a simple method: add up the cable factors for every cable, then pick a conduit whose conduit factor is equal or larger for the length of run and number of bends.
Pro tip: If you are unsure between two sizes, go up one. The extra cost is small, pulling is easier, and you have room to add a circuit later.
Light or heavy gauge PVC conduit?
Rigid PVC conduit comes in two wall thicknesses. They look the same from the outside, so check the label or product description.
| Light gauge | Heavy gauge | |
|---|---|---|
| Wall thickness | Thinner | Thicker |
| Impact and crush resistance | Lower | Higher |
| Where to use | Protected areas where it will not be knocked, such as above ceilings | Surface runs at low level, garages, workshops, commercial and outdoor work |
| Bending spring | Light gauge spring | Heavy gauge spring |
| Cost | Cheaper | Slightly dearer, but the usual trade choice |
For most surface work at or below head height, specify heavy gauge. Light gauge is fine in roof spaces and other places where nothing will hit it, but it is more likely to crack if knocked.
White or black PVC conduit?
Colour is not just about looks:
- White is the standard choice indoors. It blends with painted walls and ceilings and matches white boxes and accessories.
- Black is the usual choice outdoors. The carbon-black pigment helps the PVC resist ultraviolet (UV) light, which makes ordinary PVC brittle and discoloured over time.
- Grey and other colours are available for specific trades or to match a finish.
Some white conduits are UV stabilised, so check the datasheet before using white outside. Whatever the colour, use matching fittings from the same system so the joints fit properly.
Which PVC conduit fittings do you need?
A plastic conduit system is only as good as its fittings. These are the parts you will need on most jobs:
Couplers
Couplers join two lengths of conduit, such as this 20mm PVC coupler. Joints are usually solvent welded with PVC conduit cement for a permanent, sealed joint. Expansion couplers allow the conduit to slide as it expands and contracts.
Circular boxes
Circular conduit boxes let you change direction, branch off, mount an accessory or pull cables. Common types are the terminal (end) box, angle box, tee box, through box and intersection box, such as this 20mm PVC terminal box. Many have a standard 50.8mm fixing so you can fit a lid, ceiling rose or light fitting.
Bends and inspection fittings
Factory bends and slip bends give a neat, consistent radius where a spring bend would be awkward. Inspection bends and inspection tees, like this 25mm PVC inspection bend, have a removable cover so you can draw cables in and inspect the run later.
Saddles and clips
Saddles fix the conduit to the surface. Snap saddles are quick to fit, while spacebar saddles hold the conduit slightly off the wall so it can move with temperature changes and sit neatly over uneven surfaces. Browse our cable and conduit clips for more options. Space supports to the manufacturer’s guidance and the IET On-Site Guide, and add one close to each box and bend.
Adaptors and glands
Male and female adaptors connect conduit to enclosures, consumer units and switchgear. Flexible conduit uses its own glands or fixed and swivel adaptors to make a secure, sealed connection.
How do bending springs work?
A bending spring is a tightly coiled steel spring that you push inside rigid PVC conduit. It supports the wall as you bend so the tube keeps its round shape instead of kinking. Springs must match both the size and the gauge of the conduit, for example a 20mm heavy gauge spring, a 20mm light gauge spring or a 25mm heavy gauge spring.
- Tie a draw cord to the eye of the spring so you can pull it back out.
- Push the spring in until its middle sits where you want the bend.
- Warm the conduit in cold weather by working it in your hands or with a warm cloth. Cold PVC is more likely to crack. Never use a flame.
- Bend slowly over your knee, overbending a little, then ease back to the angle you need.
- Twist and pull the spring out with the cord. Twisting it slightly tightens the coil and helps it release.
For tight or repeated bends, use factory bends or inspection bends instead. Our conduit installation guide covers measuring, setting and drawing cables in detail.
What is LSF / LSZH conduit?
Standard PVC burns with thick black smoke and gives off acidic, halogen-based fumes. That makes escape harder and can damage equipment. Low smoke and fume (LSF) and low smoke zero halogen (LSZH) conduits are made from materials that produce far less smoke and no halogen gases.
Specify LSF or LSZH conduit for escape routes, schools, hospitals, offices, public buildings, tunnels and anywhere the project specification asks for it. An example is this Univolt 25mm heavy gauge white LSF conduit. Use LSF or LSZH cables and fittings alongside it to keep the whole system consistent.
Safety: BS 7671 requires wiring systems to be supported so they will not collapse early in a fire. Where PVC conduit runs overhead or in escape routes, check whether you need metal (non-combustible) fixings or supports in addition to plastic saddles.
Can plastic conduit be used outdoors?
Yes, if you pick the right product and allow for the weather. Follow these points:
- UV stability. Use conduit and fittings that the manufacturer states are UV stabilised and suitable for outdoor use. Black is the usual choice.
- Expansion. PVC expands and contracts much more than steel as the temperature changes. On long runs exposed to sun, fit expansion couplers and use saddles that let the conduit move, or the run can bow between fixings.
- Temperature range. PVC gets brittle in cold weather and softens in heat. Check the temperature range on the datasheet and avoid installing in freezing conditions.
- Water. Seal joints and boxes, use IP-rated enclosures and glands, and add drainage points where condensation could collect.
- Mechanical damage. Use heavy gauge conduit where it could be knocked, and consider steel at low level in busy yards or driveways.
For more on outdoor runs, read our guide to outdoor cable conduit. Standard PVC conduit is not designed for burying. For buried cables, see our guide to underground cable conduit and ducting.
Can you use plumbing PVC pipe as electrical conduit?
No. Plumbing and waste pipe is made to different standards, in different sizes, and is not tested or marked for use as an electrical wiring system. It will not fit standard conduit boxes, adaptors or bending springs, and it has not been tested for the impact, fire and electrical properties that BS EN 61386 covers. Always use conduit sold for electrical work.
Plastic or steel conduit: which should you choose?
Both have a place. This comparison shows when plastic conduit makes sense and when steel conduit is the better choice.
| Factor | Plastic (PVC) conduit | Steel conduit |
|---|---|---|
| Corrosion | Will not rust; good in damp, coastal and farm buildings | Galvanised finish resists rust, but damage to it can corrode |
| Mechanical protection | Good (heavy gauge), but can crack or crush under heavy impact | Very high; the choice where damage is likely |
| Earthing | Not conductive; run a separate cpc | Can be used as the protective conductor if installed and tested correctly |
| Heat and fire | Softens with heat; standard PVC gives off smoke and fumes in a fire | Non-combustible and keeps its shape in heat |
| Installation | Light, cut with a hacksaw, bent cold with a spring, solvent-welded joints | Heavier; needs threading and a bending machine |
| Cost | Lower material and labour cost | Higher material and labour cost |
Choose plastic for domestic and light commercial surface wiring, damp or corrosive locations, and jobs where speed and cost matter. Choose steel where cables face heavy mechanical risk, high temperatures, or a specification that calls for a non-combustible system. Our guide to metal cable conduit covers the steel options.
Which cables go in PVC conduit?
In the UK and Ireland, the cable most often drawn into conduit is single-core PVC or LSF insulated cable (6491X or 6491B, H07V-U or H07V-R). Twin and earth and flex can also be run in conduit for protection.
- Run a separate earth. PVC conduit is not conductive, so it cannot be the circuit protective conductor. Include a green and yellow cpc with every circuit.
- Keep circuits identified. Use the correct colours (brown, black, grey for line, blue for neutral) and label at boxes.
- Allow for heat. Grouping many circuits in one conduit reduces how much current each cable can carry. Apply the rating factors in BS 7671.
- Draw in carefully. Use a draw wire or draw tape, keep cables straight and untwisted, and pull through inspection fittings on long runs.
Checklist for buying plastic cable conduit
- Map the route and count the cables and sizes for each run.
- Pick the size with the On-Site Guide cable and conduit factors.
- Choose the gauge: heavy for exposed work, light only where protected.
- Choose the colour and material: white indoors, black or UV-stabilised outdoors, LSF or LSZH where smoke matters.
- List the fittings: couplers, boxes, bends, saddles, adaptors and solvent cement.
- Add the tools: the right bending spring, a hacksaw or conduit cutter, and a draw tape.
- Check the regulations for the job. Work must meet BS 7671 (I.S. 10101 in the Republic of Ireland). New circuits can be notifiable, so use a qualified electrician if in doubt.
Key takeaways
- Plastic cable conduit is a PVC tube that protects and routes cables, and it is essential when you use single insulated cables.
- Use rigid PVC for neat surface runs and flexible conduit for final connections and awkward routes.
- 20mm and 25mm cover most work; size conduit with the cable and conduit factors, not by eye.
- Heavy gauge suits most exposed work; always match the bending spring to the size and gauge.
- Use black or UV-stabilised conduit outdoors, allow for expansion, and specify LSF or LSZH where smoke matters.
- PVC conduit is not an earth: always run a separate cpc. Choose steel where heat or heavy impact is a risk.
Choosing the right plastic cable conduit
The right plastic cable conduit comes down to a few clear choices: rigid or flexible, the correct size, heavy or light gauge, the right colour or LSF material, and a complete set of matching fittings. Get those right, support and seal the run properly, run a separate earth, and a PVC conduit system will protect your cables for years. Where heat or heavy impact is a concern, steel is the better choice.
Shop plastic and flexible conduit
Rigid PVC and LSF conduit, flexible conduit, circular boxes, couplers, saddles and bending springs. Trade prices, next working day delivery across NI & ROI on in-stock orders before 5pm.
Shop plastic conduit Shop flexible conduitNeed help choosing? Call our team on 028 8675 1515 (048 from ROI), Monday to Friday, 8am–5pm.
FAQs
What size PVC conduit do I need?
20mm conduit suits most domestic lighting and socket runs with a few single cables, 25mm gives room for more cables or larger sizes, and 32mm suits heavier submains and busy runs. Work out the size with the cable factor and conduit factor tables in the IET On-Site Guide rather than by eye.
What is the difference between light and heavy gauge PVC conduit?
Heavy gauge conduit has a thicker wall, so it resists impact and crushing better and is the usual choice for surface runs in garages, workshops and commercial sites. Light gauge is lighter and cheaper but only suits areas where it is unlikely to be knocked. Always use the bending spring that matches the gauge.
Can I use white PVC conduit outdoors?
Only if the manufacturer says it is UV stabilised and suitable for outdoor use. Black PVC conduit is the usual outdoor choice because its carbon-black pigment resists sunlight better. Outdoors you should also seal the system, allow for expansion on long runs and use fittings rated for the same conditions.
Is PVC conduit an earth?
No. PVC is an insulator, so the conduit cannot act as a circuit protective conductor. You must run a separate earth (cpc) with the circuit conductors, usually a green and yellow single cable, and connect it at every accessory and box that needs an earth.
How do you bend PVC conduit without kinking it?
Push a bending spring of the correct diameter and gauge into the conduit, tie a draw cord to it, then bend the conduit slowly over your knee, overbending slightly and easing back. In cold weather, warm the conduit gently first. Never use a flame, and use a factory bend where the radius is tight.
When should I use steel conduit instead of plastic?
Choose steel where cables need strong mechanical protection, where temperatures are high, where a non-combustible system is specified, or where the conduit is to act as the protective conductor. Plastic is better for damp or corrosive locations, quick domestic and light commercial runs, and when weight and cost matter.