Topic: electric cables

Check list after completing an electrical system

When wiring a building, strict rules and safety checks must be observed to ensure that the building is up to standard. These measures are essential to ensure the safety of people who use these spaces or that are nearby. In this way, it is possible to protect and prevent any faults, malfunctions and problems that may compromise both functionality and general safety.

Precisely for this reason, by law additional checks are carried out once the electrical installation has been completed and the building has been wired, whatever its intended use.

Once the wiring of the building has been completed, it is necessary to draw up an adequate list of the checks to be carried out room by room: the objective is to verify that all the elements of each space present the correct wiring and that the notes have been met accurately for every position of the device.

At the same time, check that all the protections are active. In particular, it must be verified that in each room the reference standards are respected.

First of all, pin-to-pin connectivity must be verified by referring to the standards in question. Once you have chosen the appropriate scheme you must follow it for the entire network. The goal is to ensure continuity of the wiring, so that each pin is connected to the other part of the cable, specifically to its equivalent.

At this point it is necessary to carry out the qualitative checks on the transmission of the signal, making sure that there are no defects in the network or in a cable, such as:

  • an inverted torque, ie the most common error;
  • a transposed pair, which occurs when the connection of the coupled pair involves a completely different element. It usually occurs when the pins are incorrectly counted. Alternatively, it may happen that you enter the crossover incorrectly to put two hubs in communication;
  • you do not use an uplink port to connect the hubs to each other.

Noises in the transmission and reception of the signal occur when the electrons do not travel at constant speed, causing reflections, losses or interruptions. In these cases, the TDR test is used, which allows to measure the length of the connection and to determine the distance from the point of detection of any signal interruptions or short circuits.

A tester is used to send a pulse signal along the cable and measure the time needed for signal return. Then the results are compared with the standard delay values; there is an anomaly when the preset limit is exceeded. On the other hand, when talking about signal attenuation, it is necessary to determine whether the problem affects an element close to the transmission or reception point.


Post-wiring checks

As you can see, there are many critical installation problems that can develop during construction, so a proper wiring and using high quality components is not sufficient to guarantee a functional and fast network. Precisely for this reason it is necessary to realize a post-wiring control. This is a test which must affect all the sockets and cables of the building.

Among the most suitable tools for these operations are the field testers, devices for measuring the electrical network, composed of a slave and a master. The first is a signal injector, while the second consists of a keyboard and a display. These devices also serve to check the connection class of the system in accordance with the provisions of ISO 11801.

Only through the use of the elements belonging to the corresponding category can we guarantee the respect of the characteristics and the performances of the whole of the installed parts. There are seven ISO classes, which are distinguished by different speeds, that is:

  • class F2000 +, with an intensity up to 600 MHz;
  • class E2000 +, from 100 to 250 MHz;
  • class D2000 +, up to 100 Mhz in case Gigabit Ethernet solutions are adopted;
  • class D, up to 100 Mhz when it comes to high-speed solutions;
  • class C, from 1 to 16 Mhz (high speed applications);
  • class B, for solutions not exceeding 1 MHz (medium speed);
  • class A, for solutions that do not exceed 100 khz (low speed).


Consequently, once the wiring is done, field testers must be used to perform specific checks through a wide range of tests. These include:

  • loss of signal for reflections (return loss);
  • the wire map (map of the connections of the binary pairs of cables);
  • signal attenuation;
  • the impedance;
  • the NEXT at both ends of the cable;
  • the lenght link (evaluation of the length of the connections);
  • the propagation delay of the signal (propagation delay);
  • the ACR (Attenuation to Cross talk Ratio), that is the ratio in a pair of cables close between the useful signal power and that of the dissipated signal and that must be as high as possible to guarantee a performance transmission.

Remember that the instrument performs these checks by repeating them on all frequencies, but the display shows only the worst result. This is a precaution necessary for practical and security reasons.

There is however a solution to start from a higher level of safety, thus allowing us to avoid some of the aforementioned checks - because this technology will no longer be necessary: I am talking about the prewired cable already widely used in most areas of Europe, such as France or Belgium - which can revolutionize the concept of wiring and installation.

Find out what benefits it can guarantee!

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Posted by Redazione on December 11, 2018

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