What this guide covers
You can make the design process easier by collecting appliance information and measuring the intended route. Those details give an electrician a useful starting point before materials are ordered.
Stop using affected equipment if there are hot connections, discolouration, damage or repeated trips. Arrange an assessment before increasing the load or replacing protective devices.
Copy or print your summary
You can make the design process easier by collecting appliance information and measuring the intended route. Those details give an electrician a useful starting point before materials are ordered.
Cross-section and outside diameter are different measurements
A cable may be marked 3G2.5. In that common designation, 3 describes the number of cores, G indicates a green-yellow core and 2.5 is the nominal conductor cross-section in mm². An example Draka datasheet lists this construction. Check the actual datasheet: the complete cable marking contains further information.
The figure 2.5 mm² does not mean the cable measures 2.5 mm across. To assess whether a cable fits into a conduit, you need its actual outside diameter. Connections also depend on conductor construction and the terminal's accepted sizes.
A multicore cable, individual installation wire and flexible appliance cord are different products. Matching cross-section markings do not make them interchangeable.
Collect the information needed for the design
| Information | What to prepare |
|---|---|
| Appliance | Make, model and installation instructions. |
| Electrical demand | Rated power and current, plus other equipment sharing the supply. |
| Route | Measured length, including rises and changes of direction. |
| Installation environment | Indoors, outdoors, underground, conduit, wall or thermal insulation. |
| Use | Occasional, sustained or simultaneous with other substantial loads. |
| Existing installation | Available drawings and records of previous work. |
The electrician then assesses protection, heat dissipation, voltage drop and fault protection, among other requirements. Prysmian describes comparable inputs for its professional cable calculation system. Prysmian: CableApp.
Keep the consumer unit closed while gathering information. A photograph of its closed front and existing records can help prepare the discussion. Missing electrical characteristics need to be established on site.
Why heat and distance affect the answer
A cable in a warmer environment has less scope to lose heat. Grouped loaded cables and routes through thermal insulation can also change the conditions. The appropriate current capacity may differ from that of a similar-looking cable elsewhere.
On a longer route, voltage drop also needs assessment. During a fault, the installation and its protective device must work together appropriately. Looking at the amount of copper does not answer those questions.
Increasing cross-section is not a complete solution either. Terminals must accept the conductor, the cable must suit the environment, and its bending radius and installation requirements must be respected.
Calculate a purchase length without guessing the cable size
Suppose an agreed route includes 8 m horizontally, a 3 m rise and a further 5 m along a wall. The route totals 16 m. If the electrician specifies another 2 m for the ends and installation in this design, the planned purchase length becomes 18 m.
The material-length tool can add these measurements. It does not select a cable type or cross-section. The extra 2 m is an assumption for this example, rather than a universal installation allowance.
Conduit sold in fixed lengths also needs a cutting plan. Five 4 m lengths total 20 m, but short offcuts may not suit the remaining sections of your route. Record bends, joints and accessible ends as well as the total distance.
For a useful quote, identify which parts of the route are already accessible and which require opening a wall, floor or ceiling. This can affect the work more than a small difference in cable price.
Conduit and connectors are part of the specification
Dutch electrical conduit systems include 16, 19 and 20 mm sizes. Usable internal space varies between products and between rigid and flexible conduit. Pipelife documents different interfaces, while TKF distinguishes rigid and flexible conduit in its practical guidance.
Do not order on outside diameter alone. Specify cable, conduit, bends, boxes and terminations as a compatible system. Each shopping-list entry should contain an exact type and quantity.
Frequently asked questions
Can watts divided by 230 tell me the required cable size? For some loads it gives a simplified current estimate. It does not assess every factor needed for cable selection or safety.
Is a thicker conductor always preferable? Suitability also depends on terminals, installation method and protective measures. Materials need to match the design.
Can I fit a larger breaker when a circuit keeps tripping? Have the cause investigated. A different breaker can leave the existing wiring inadequately protected.
Stop using affected equipment if there are hot connections, discolouration, damage or repeated trips. Arrange an assessment before increasing the load or replacing protective devices.
Discuss your cable route with CAS
Tell CAS Elektrotechniek what you want to connect, the appliance model, the route measurements and how you expect to use it. Discuss your installation with CAS.
Sources
Materials and specifications
Before buying, check that the size, type and specification suit your installation. Use the article list and tools to work out the quantities you need.
Tape measure and plan
- Quantity and unit
- One tape measure and current plan
- Specification
- Survey accessible surfaces only; measurements do not establish electrical suitability.
Manuals and model details
- Quantity and unit
- One current manual per exact product
- Specification
- Use exact model/revision, with conflicting instructions unresolved until manufacturer/installer clarification.
Installation wire or cable
Specified by the electrician- Quantity and unit
- Separate measured quantities per complete specification
- Specification
- Conductor material/class/cross-section, colours, insulation, installation method and product approval; never infer from wattage alone.
- Elektramat · Alle kabels
View range - HORNBACH · Draad & kabels
View range - KARWEI · Installatiekabels
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Plan route quantities
Keep each material, colour and cross-section separate. Specification is still required. A total is not a cutting plan, continuous reel length or conduit-fill calculation. Allowances and contingency are your planning choices, not installation rules.
Worked example and formula
4.2 + 2.8 + 1.5 m plus two 0.3 m allowances = 9.1 m. With a user-chosen 10% contingency: 10.01 m. A 4 m light line and 1.2 m supply route stay separate.
planned m = (sum of measured m + explicit allowances m) × (1 + contingency / 100)
Formula version 2026-10-05.1
Sources
Would you like CAS to carry out the work?
Tell us about the room, equipment and changes you need. Agree the work, checks and warranty terms before the job starts.
Discuss the workIn the event of fire or immediate danger: move to safety and call 112. Do not wait for a form reply.