Topic: electric cables, electricity sector, electrical equipment

How to calculate the meters of prewired conduit needed in a home

When corrugated conduits must be laid for a system in a home, there are several things that must be programmed and calculated.

The first of these is of course the quantity of corrugated pipe, and the diameter of the same, which will be used inside the house. This is exactly what we are going to calculate with practical examples in this guide, in which we will also evaluate other fundamental aspects to take into consideration when arranging corrugated items. For example the color of the pipes to be chosen as well as the reference legislation.


One corrugated for each cable

Corrugated pipes are flexible pipes (also called flex) necessary when cables must be passed under the floor or in the wall according to routes to be established.

Inserting cables into corrugated pipes is not only a choice that serves to protect the cables themselves, which is also necessary but also a time-saving and useful solution in the event of future cable replacements or additions.

In fact, inserting the cables in a tube that houses them also means being able to pull them out in case of need without destroying the installation itself, floor  or wall, or worse, removing all the cables just to replace one. Different types of cables can be passed through corrugated; there are the electrical cables for the electrical system, those for the plumbing services, those for example for the intercom, and so on.

The type of system, according to the cables housed by a corrugated board, can be distinguished according to the color chosen for the host corrugated board: this is useful both for keeping under control the type of system that we could change in case of need, but also and above all refer to the international standards on safety and homologation of the pipes themselves, namely the CEI 64-8 and 64-100 / 2 standards.


And a color for every type of plant

A short summary that identifies the internal cable according to the external corrugated:

  • Black corrugated, which can sometimes be replaced with the gray cable: electrical cable for the lighting and handling system (i.e. for example the electric shutters);
  • green corrugated, which can sometimes be replaced with the white one: telephone and television system;
  • corrugated blue: intercom system;
  • brown corrugated: security system and various alarms;
  • purple corrugated: used for the audio and video system cables but only for houses equipped with a home automation system.

The distinction in various colors also presupposes that functional cables to different systems are not all inserted in the same corrugated. Although speaking of diameter it could be done, it can happen that the cables, all within the same corrugated, could i disturb the signal mutually.

The advice is to insert, when placing the corrugated materials, at least one empty pipe, which could be used later without having to break walls or floors.


Calculation of the diameter of the corrugated pipe

We will see now how to calculate which corrugated pipe is needed in a home. For this calculation, for which an expert wholesaler can give useful indications, we start with the diameter. The diameters found on the market are from 16 sq. Mm and can reach 63 sq. Mm.

The most used intermediate sizes are: 20mm, 25, 32, 40, 50, 63.

The first thing to do is to calculate the internal space of the corrugated, where the cables will pass. It is also important to provide an additional space that acts as an air chamber for heat dissipation.

The reference standard is CEI 64-8, which is applied for the use of copper electric cables, and the combined formula is:

(Average cable diameter x Number of cables) times 1.5.

Let's take a practical example: 5 3.00mm cables must be inserted.

The first thing is to calculate the average diameter of the cables, which will be (3 + 3 + 3 + 3 + 3)/5, then multiply it by the number of cables (5) and finally times 1.5.

So: 15/5 = 3 x 5 = 15, for 1.5 = 22.50.

This is the minimum value of the tube diameter to use, preferably larger. In general, it is used to add 10% more in sections longer than 10 meters.

The reference standards for corrugated pipes

A last the reference standards that regulate the use, and therefore the production, of corrugated products.

The CEI 64-8 applies precisely to residential environments.

According to this standard, the pipes must be such as to allow the cables to be easily pulled out inside. The internal diameter of the protective pipes must be one and a half times (at least) the diameter of the cable bundle. The resistances and the intended uses are indicated with colors (and in this case the reference standards are CEI 64-8 and 64-100 / 2).

There are 12-digit classification codes that are used to identify the specific properties of the tube:

  • Digit 1: compressive strength
  • Digit 2: impact resistance
  • Digit 3: low temperature range
  • Digit 4: high temperature range
  • Digit 5: resistance to bending
  • Digit 6: technical characteristics
  • Digit 7: protection from the entry of solid bodies
  • Digit 8: protection against water infiltration
  • Digit 9: corrosion resistance
  • Digit 10: tensile strength
  • Digit 11: resistance to flame propagation
  • Digit 12: resistance to suspended loads.

It should be specified that the legislation does not prohibit the use of a different color for a specific cable (for example green for electrical cables).

However, the good sense of a good installer, supported by the designer, will ensure that the cables are always distinguished by color to allow more functional maintenance.

The length of the corrugated pipe will be calculated on the basis of both the square meters of the apartment, of course, but also on the basis of the layout of the system. And here we can refer to the designers' schemes.


It is important to consider all the elements mentioned above well so that you are not in the situation of having to recalculate additional meters of pipes, or worse, have the wrong diameter with respect to the needs, without considering the further economic outlay that would result. It will, therefore, be necessary to rely on competent installers and suppliers.

For further curiosity then, considering using the prewired conduit, in addition to the advantages of saving time and operating safely, at this link you can find an example of the savings calculated on an 80 sqm apartment using MonFlex prewired pipes. Without considering that with MonFlex prewired conduits, you will have experts who will calculate for you the best diameter to use in relation to your needs.

how to simplify your electrical system wiring  discover mon flex precabled conduit


Posted by Redazione on August 5, 2020

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