When it comes to operating electrical devices and systems efficiently and safely, it is important to know the maximum possible current carrying capacity of a cable or conductor. As a rule of thumb, the maximum current carrying capacity depends largely on the cross-section of a conductor. In concrete terms, this means that the larger the cross-section of the conductors in a cable, the greater the current carrying capacity.
In addition to the cable cross-section of a copper or aluminium conductor, other factors such as the respective ambient temperature and the insulation material used also play a decisive role.
This guide summarises the most important details on the definition of current carrying capacity, current carrying capacity and other important information on how the maximum current load of a cable is determined.
Why is it important to lay out protective hose correctly?
The correct design of the protective tube ensures safety in electrical installations by minimising potential hazards and implementing protective mechanisms against various risk factors. Let's take a closer look at what these hazards are:
Mechanical protection: a conduit protects the cables installed in it from mechanical impacts, such as pressure, bending and external damage. If protection is not provided, the cable insulation may be damaged, resulting in short circuits and other faults.
Prevention against environmental influences: The protective tubes act as a barrier against environmental influences such as moisture, dust, chemicals and UV radiation. Incorrect selection or sizing leads to insulation degradation, which not only affects the performance of the wires, but also increases the risk of corrosion and other potentially dangerous reactions.
Fire prevention: A correctly dimensioned protective tube also helps to prevent the spread of fire. The right choice of material plays a decisive role here, as certain protective tubes can have flame-retardant properties.
EMC protection: Electromagnetic compatibility (EMC) is an important factor, especially in industrial environments. A well-chosen protective tube supports the need to minimise electromagnetic interference and increase the reliability of electrical systems.
In summary, the correct design of a protective tube helps to extend the service life of electrical wires, ensure operational safety and minimise potential risks to people and equipment.
The correct lay out of a protective tube in 10 steps
Follow the step-by-step instructions below to correctly design a protective tube. It will help you to avoid common mistakes in the protective conduit design and improve the service life and safety of the installations.
- Environmental analysis: Analyse the environmental conditions, including temperature, humidity and chemical influences.
- Number and types of cables: Determine the number and types of cables to be protected to select the appropriate diameter.
- Standards and regulations: Review applicable standards to ensure the protective tubes meet safety standards.
- Material selection: Select the appropriate material, also based on environmental and potential chemical exposures.
- EMC requirements: Consider electromagnetic compatibility for applications with interference risks.
- Diameter calculation: Calculate the required diameter based on the number of cables, cable type, cable cross-section and future extensions.
- Installation requirements: Observe the installation conditions with regard to bends and fastening methods.
- Specialist advice: Consult experts or manufacturers for customised recommendations if you are unsure.
- Documentation: Record your decisions, calculations and selection criteria for future reference.
- Regular inspection: Regularly monitor the condition of the protective tubes and carry out maintenance work if necessary.
Comparison of the different types of protective tubes and their suitability for different applications
Whether automotive and mechanical engineering, energy supply, food industry or telecommunications - protective tubes provide customised protection for cables and wires in different industries and areas of application. The following list, which shows the properties and materials for the specific applications, shows the different types of protection.
The different types of protective tubes and their applications:
- PVC cable conduit: Suitable for protection against mechanical loads and lighter environmental influences. They are often used in office environments and industrial applications.
- Protective metal conduits: Offer high mechanical strength and are well suited to demanding environments with heavy mechanical loads, high temperatures or aggressive chemicals. Typical applications include industry and mechanical engineering.
- Silicone protective tubing: Characterised by their high temperature resistance and are therefore often used in applications involving extreme heat or cold. Typical areas of application are the food industry, medical devices and high-temperature applications.
- Braided sleeving: Consists of a metal or plastic braid and offers protection against mechanical influences as well as a certain degree of flexibility. They are used for applications in the automotive industry, electronics and telecommunications.
- Thermoplastic protective tubes: Offer good flexibility and are suitable for applications where higher chemical and heat resistance is required. They are often used in the food and automotive industries.
- Nylon protective tubes: Are lightweight and flexible while offering good resistance to mechanical wear. They are used in the automotive industry and in mechanical engineering.
- Corrosion-resistant protective tubes: Are specially developed for use in environments where corrosion is a problem. They are used in maritime applications, chemical plants and other corrosive environments.
- EMC protective conduit: Electromagnetically compatible protective tubes are used in environments where minimising electromagnetic interference is important, as well as for devices with highly sensitive electronics.
How do you determine the right sizes for protective tubes?
Questions that have to be answered every day in practice: How many cables fit into an empty conduit?
The sizes and diameter of empty conduits are closely matched to the number of electrical cables that are to run through them to ensure effective and safe coverage. Firstly, it is therefore important to know the exact number and diameter of the cables that are to be protected. A simple rule of thumb is that the internal diameter of the protective tubes should be at least 20% larger than the diameter of the largest cable or bundle of cables to provide sufficient space.
When matching the conduit size to the number of cables, it is also important not only to know the actual requirements, but also to take future expansions into account. The protective tubes should therefore provide additional space. It is also advisable to analyse the specific requirements of the environment, including possible mechanical stresses, chemical influences, temperature fluctuations and other environmental factors, to ensure the appropriate material selection and sizes of the protective tubes. In any case, a precise understanding of the number of cables, their diameters and the environmental conditions is crucial in order to select the optimum protective tubes with the right sizes for the specific application.
In case of uncertainties or complex requirements, we recommend consulting experts or manufacturers to ensure that the protective tubes meet the individual needs. For a rough calculation of the number of NYM-J cables in the empty conduit, please refer to the following table.
| Empty conduit sizes | Outer diameter (OD) |
Inner diameter (ID) |
Product |
NYM-J 3x1.5mm² |
NYM-J 5x1.5mm² |
NYM-J 7x1,5mm² |
|---|---|---|---|---|---|---|
| M16 | approx. 16mm | 12 mm | 10233202012 |  |
 |
 |
| M20 | approx. 20mm | 16.5 mm | 10233202016 |  |
 |
 |
| M25 | approx. 25mm | 22 mm | 10267232023 |  |
 |
 |
| M32 | approx. 32mm | 27.5 mm | 10267232029 |  |
 |
 |
Download table
NOTE:
The inner and outer diameter of the empty conduits may vary depending on the manufacturer. Depending on the material procurement, material shape and material thickness, the diameters can differ greatly in some cases.
This also applies to the diameter of the cables. Here is just a brief overview of how the cable cross-sections can vary.
| Lapp |
Whole cable |
Cable type |
|---|---|---|
| NYM-J 3x1.5 mm² | ⌀8,2mm to 9,9mm | ⌀9.1 mm |
| NYM-J 5x1.5 mm² | ⌀9.5mm to 11.5mm | ⌀10.3 mm |
| NYM-J 7x1.5 mm² | ⌀10,5mm to 12,6mm | ⌀11.5 mm |
Tips and tricks for choosing the ideal protective tubes
Do you need more tips to help you choose the ideal protective tubes? Answer the following questions to make the ideal choice:
- How flexible does the electrical conduit need to be to meet the installation requirements, especially bends or changes in direction?
- In what temperature range will the protective tubes be used and how well prepared is it for extreme temperatures?
- Is the protective tube used in outdoor applications or in areas exposed to direct sunlight, and how well is it protected against UV rays?
- What fire protection requirements apply to the application and does the protective tube comply with the relevant standards and certifications?
- What chemical influences is the protective tube exposed to and how resistant is it to the specific chemicals in the environment?
- Are electrostatic charges a potential problem and how well can the protective tube provide reliable grounding?
- Is the design of the protective tubes such that inspections and maintenance can be carried out practically?
- Are electromagnetic compatibility requirements relevant and how well does the protective tube fulfil these requirements?
- What is the environmental impact of the protective tubes and are there environmentally friendly material options or recycling possibilities?
- What certifications, standards and recommendations does the manufacturer provide for the protective tubes, and do these meet your specific application requirements?
How do you utilise the flexibility of the protective tubes?
The flexibility of the protective tube makes it easy to lay around corners and bends without kinking or damage. This is particularly important in installations that require irregular shapes or complex runs, as well as when laying over longer distances where the protective tubes need to be routed through various components, machines or structures. A flexible protective tube is also a good choice in environments with limited space or in confined areas, as it can be easily adapted to the spatial conditions. Corrugated tubing or corrugated tubes are particularly suitable as flexible protective tubes. Divisible corrugated tubes or split corrugated tubing split are particularly suitable for easy subsequent insertion of cables.
What factors should you consider to determine the number of cables in the empty conduit?
Determining the number of cables that can be laid in an empty conduit requires careful consideration of several factors. Cable diameter and empty conduit diameter obviously play the biggest role. However, don't just evaluate current needs, but also think about future expansions to ensure the necessary flexibility for changes and additional cables. The flexibility of the conduits themselves is also a factor, especially for installations with many bends or obstacles.
Calculating the correct conduit diameter
Please note that there is no universal formula for calculation as requirements may vary depending on the application. In some cases, manufacturers provide specialised configurator tools to help select the correct conduit diameter, but there are also general considerations that you can always take into account when calculating:
- Number of cables
- Diameter of the cables
- Reserve for future extensions
- Environmental conditions such as temperature or obstacles
- Material of the empty conduit
But how many cables can fit through an empty conduit?
It depends on the cable diameter (outer diameter). If you know the cable diameter, you can use the inside diameter to determine which empty conduit you need. The following calculations can be used as a "rule of thumb".
For example, if your cables have an outer diameter of 13 mm, you can use an M16 empty conduit with a diameter of 16 mm (13 mm + 20% reserve). If you have e.g. 2 cables that you want to run through the empty conduit, then you must add the two outer diameters of the cables and then select the corresponding diameter.
For example, you have one cable with an outer diameter of 11.0 mm and one with an outer diameter of 10.0 mm. You therefore need an M25 empty conduit (21mm diameter + 20% reserve), as the total diameter of the cables is 21mm.
If you have 3 cables, you need to add the outer diameter of the two thickest cables to find out which diameter you need.
Differences in the design of protective tubes for different cable types
The design of protective tubes varies depending on the cable type and the specific requirements of the application. Here are some key differences in the design of protective tubes for different cable types:
Power cables: For power cables, the main requirement is often protection against mechanical damage and external influences. Robust protective tubes with high impact resistance and resistance to environmental influences are preferred here.
Communication cables (e.g. data cables): Communication cables require protective tubes that can shield against electromagnetic interference (EMI) in addition to mechanical safety. Electromagnetically compatible (EMC) protective tubes with appropriate shielding properties are relevant here.
Coaxial cables: Coaxial cables, which are generally used for the transmission of signals, require special protective tubes that provide good shielding against electromagnetic interference and ensure signal integrity.
Control cables: For control cables, the flexibility of the protective tube is often important, especially if the wires are used in moving machinery or equipment. Flexible protective tubes made of materials such as PVC or PUR are often suitable here.
Fibre optic cables: Fibre optic cables require special protective tubes that protect the sensitive glass fibres despite bends and ensure low attenuation. The protective tubes should also protect against external influences such as moisture.
High-temperature cables: Cables that are exposed to high temperatures require protective tubes with high temperature resistance. Materials such as silicone or PTFE (polytetrafluoroethylene) are used here.
Low-voltage cables: In the case of low-voltage cables, insulation and protection against moisture are often the most important factors in addition to protection against mechanical influences. PVC or polyethylene protective tubes may be suitable here.
Special cables: Special cables, such as those used in medical technology, often require protective tubes with high flexibility, biocompatibility and possibly special hygiene requirements.
Tips for laying cables in empty conduits
Use the following approaches to make cable laying in empty conduits easier:
Use cable lubricant: Using lubricant can reduce friction and makes laying cables in empty conduit much easier. Take advantage of this, especially if you have to run several cables through longer empty conduits. Make sure you choose a lubricant that is compatible with the cable types and the material of the conduit.
Consider the bend radius: Each cable type has a recommended bend radius to prevent damage or degradation of signal quality. Check the manufacturer's specifications for the cables and make sure that the bending radius corresponds to the recommended values.
Label the cables for easy identification: Before inserting the cables into the empty conduit, label them clearly and unambiguously. This not only makes it easier to identify individual cables during installation, but also for future inspections, repairs or extensions. Use coloured cable ties, labelling or other suitable marking methods according to the requirements of your installation.
How do you prevent overfilling or underfilling of the protective tubes?
Efficient and long-term planning in the installation not only ensures optimum utilisation of the protective tubes, but also quality, safety and economy. Therefore, avoid overfilling and thus ensure the integrity of the cables and minimise the risk of damage. If the protective tubes are underfilled, this in turn has an impact on the mechanical protection of the wires they contain. These can form kinks or unnecessary bends and cause damage. The tensile stress is also impaired and leads to premature wear. Correct filling, on the other hand, ensures targeted mechanical, thermal and electrical insulation of the cables. Observe the following measures:
- Carefully determine the number of cables to be routed through the protective tubes and the diameter of each cable.
- Once you know how many cables are to be laid in the protective tube, plan a reserve space for possible extensions.
- Keep precise documentation of the cables laid in the protective tubes. This way, you will always know the fill status of the protective tubes so that you can refer back to them during subsequent installation measures.
- Select a protective tube that has the necessary flexibility and characteristics with regard to environmental conditions.
- Pay attention to the applicable standards and regulations. Standards provide clear guidelines for the maximum permissible number and minimum diameter of cables in protective tubes. For example, DIN VDE 0298-4 (Deutsche Industrie Norm Verband der Elektrotechnik) contains information on various aspects of electrical installation, including the selection and installation of cables, protective conduits and tubes.
The importance of the protective conduit length: How do you measure correctly?
Not only the diameter, but also the length of the protective tube plays an important role in the installation of cables. A correctly measured protective conduit length not only ensures protection against external influences such as mechanical stress and moisture, but also flexible freedom of movement for the cables.
Measuring the protective conduit length requires precise consideration of the entire cable route, additional lengths for bends and movements as well as a reserve for possible future extensions. Careful planning ensures that the protective tube covers the cables and thus guarantees a long-term, reliable installation.
How to measure the protective conduit length correctly: The process begins with an accurate measurement of the entire length of the cables to be protected, carefully considering possible bends and runs in the cables. To do this, start with the starting point of the wires and follow it to the end point. Be sure to take into account the same route that the cables will take later, even if it is not direct or straight. Measure carefully along this route using a tape measure or ruler. For longer distances, it is advisable to mark the route first. To be on the safe side, we recommend adding a small buffer - about 10 % of the measured length - to compensate for any errors during installation and to ensure that there is enough slack.
Which materials are best suited for protective tubes?
Choosing the best material for protective tubes depends on various factors, including the specific requirements of the application, environmental conditions, cable types and industrial standards. By considering the following criteria, you can ensure that you choose the optimum material to ensure a durable and effective solution.
Temperature resistance: Depending on the application, the selected material must be able to withstand extreme temperatures. Whether heat or cold - the protective tubes should retain their properties and not be damaged.
Chemical resistance: If the protective tubes come into contact with certain chemicals, it is important that they are resistant to these substances. Make sure that the chosen material does not react or dissolve.
Abrasion resistance: Depending on the application, the protective tubes may also be exposed to mechanical loads. To ensure a long service life in such cases, the material should be robust and wear-resistant.
Flexibility: The protective tubes should be flexible enough to adapt to different shapes and allow movement without any problems.
UV resistance : If the protective tubes are used outdoors, they must be protected from harmful UV rays. The chosen material should therefore not be affected by sunlight.
What materials are available for protective tubes?
The plastics used to manufacture protective tubes are usually thermoplastics, elastomers or thermosets. Here are some materials that are commonly used for protective tubes:
- Metallic protective tubes (stainless steel, aluminium)
- silicone
- PTFE (polytetrafluoroethylene)
- Glass fibre reinforced plastics
Frequently asked questions
How can several cables be laid in one empty conduit?
Laying multiple cables in an empty conduit requires careful planning. Choose empty conduits with a sufficient diameter, adhere to the recommended bending radii and arrange the cables carefully to avoid overfilling and damage. Observe applicable standards and document the installation for future reference.
How are cables pulled into an empty conduit?
To pull cables into an empty conduit, use a pull wire or other pulling aid that is first pushed through the empty conduit. Now attach the cables to the pulling aid and pull them out of the empty conduit in the opposite direction. At the same time, you can push along the cables to make the process easier.
What is a pull wire for empty conduits?
A pull wire is a special tool that is used during the installation of cables in empty conduits. It is used to pull the cables through the pipe, especially if the pipe is curved or laid over longer distances. The pull wire is usually flexible and strong enough to be guided through the conduit while being pliable enough to follow curves.
Conclusion
Protective tubes, empty conduits and their careful design are key principles that significantly influence the success and durability of an installation. When making yourchoice, opt for high-quality materials and manufacturing standards that support your installation work and therefore never favour the lower price. Quality not only ensures a longer service life of the installation, but also guarantees reliable protection of the cables against external influences.
Despite careful editing and checking of the content, Stecker Express assumes no liability for the topicality, correctness, completeness and quality of the information provided.
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Cable / power cable colours - What do the different colours of power cables or cables in general mean?
Cable jacket
Cable sheathing & cable insulation - properties and differences of the cable sheath at a glance
Cable designation
Cable designation illuminated: This makes it easy to identify cables
AWG in mm²
Conversion of AWG cable cross-sections to mm² - Strand construction and AWG tables
Cable protection
Cable protection - 11 ways to protect cables and wires efficiently