Wire x flexible cable, short circuit test.

Which conductor is more resistant, rigid wire or flexible cable? In this article we will show a practical test of short circuit, to end this doubt once and for all, where we apply an electric current of 300A in each conductor. Come on guys!

Rigid wire x Flexible cable

The rigid wire and flexible cable are electrical conductors with different names, because they have characteristics of different internal compositions, but both with the same purpose and characteristics that is the conduction of electric current .

Rigid wires have only one solid conductor and flexible cables are made up of several smaller conductors, both made of copper and aluminum, as copper and aluminum are metals with excellent conductive characteristics of electricity.

The rigid wire and flexible cable are electrical conductors, with different internal compositions.

Practice test

In the tests we will subject a rigid wire and a flexible cable to a short circuit with an electric current of approximately 300A and we will see which one resists the longest, both conductors being 2.5mm².

It is very important to take into account that the tests that are done on cables follow the norms, that is, a cable or a 2.5mm² wire are manufactured and tested to resist a certain electrical current according to various characteristics. In the cable dimensioning tables of NBR 5410 we can see the conducting capacities of electric current of the conductors.

In the image below, see that table 36 of the NBR 5410 standard indicates capacities for conducting electric current from the conductors, in amperes for cables according to the ambient temperature, the installation method and the type of insulation. Nowhere in the table is there a differentiation between rigid wire and flexible cable.

Table 36 of the NBR 5410 standard indicates capacities for conducting electric current from conductors.

In table 36 of the NBR 5410 standard, for example, the 2.5mm² cable being used in reference method B1 with two charged cables supports 24A, regardless of whether it is a rigid wire or a flexible cable.

The 2.5mm² cable being used in reference method B1 with two charged cables supports 24A.

Now that we have explained the basics of electrical conductors, let’s go to the short circuit tests. We will carry out two tests, one with rigid wire and flexible cable together and the other with separate rigid wire and flexible cable.

Regardless of the result of our test and which will withstand the short circuit the longest, both cables can be used in electrical installations and we advise you never to repeat these tests in your home.

Before starting the test, let’s measure the electrical resistance of the rigid wire and the flexible cable. See the image below, that the flexible cable is approximately 0.2 ohm and the rigid wire is approximately 0.1 ohm.

Electrical resistance, hard wire and flexible cable.

In the first test we have a rigid wire and a flexible cable, both 2.5 mm², which will be subjected to the short circuit simultaneously, and since the two cables have very similar resistances, both will receive approximately the same electrical current.

When we connect the circuit, the conductors heat up, so the insulation layer melts and the conductors start to glow until the conductors break. In this first test the flexible cable breaks first and the rigid one afterwards.

In the first test, rigid wire and a flexible cable will be subjected to the short circuit simultaneously.

In the second test we will subject the conductors to the same short circuit, however separated. Again we are going to measure the electrical resistance of the conductors and again the flexible cable is approximately 0.2 ohm and the rigid wire is approximately 0.1 ohm.

Let’s measure the electrical resistance of the conductors.

First we will test the resistance of the rigid wire, when we connect the circuit the wire heats up, its insulating layer melts and the wire begins to glow, until the rigid wire breaks in approximately 16 seconds.

Rigid wire breaks in approximately 16 seconds.

Now we are going to test the resistance of the flexible cable, when we connect the circuit the same process of breaking the rigid wire happens, however the flexible cable broke with approximately 14 seconds, a little less than the rigid wire.

Flexible cable broke with approximately 14 seconds.

Regardless of whether the conductor is a flexible cable or a rigid wire, the time they resisted the short circuit under equal conditions was very similar. So, for this reason the standard does not distinguish between wire and cable when dimensioning.

It is a fact that during the passage of cables in the pipes of an electrical installation, the flexible cable has a great advantage in relation to the rigid wire because it is easier to pass, which in the end generates considerable savings in installation time, in addition to simplifying the execution of the service.

We know that it is very important to know how to choose a good electrical conductor, be it rigid wire or flexible cables. But unfortunately on the market there are still many cables that do not meet the standard, one of the main characteristics of a suitable electrical cable is that it does not catch fire. Below is a video from the Mundo da Elétrica channel, teaching how to identify whether a cable catches fire or not.

And you, leave your comment telling us if you prefer to work with the flexible cable or the rigid wire. If you have any questions or curiosity about the subject, leave it in the comments and we will answer it!