Where did the myth come from that sockets can only be connected with a 2.5 mm² cable

  • Mar 21, 2021

Over the past day, at least ten people were indignant, how a 1.5 mm² cable can be used in an extension cord for a current of 16A, because it will not withstand.

Today I will debunk the myth and tell you how it happened that almost all electricians connect the sockets with a 2.5 mm² cable.

My yesterday's review of IKEA extension cords (https://ammo1.livejournal.com/1229112.html ) has already been read by more than 180 thousand people, and out of more than a thousand comments on different sites, one repeats all the time: "One and a half square will not withstand 16 amperes."

We open GOST 31996-2012 "Power cables with plastic insulation for rated voltage 0.66; 1 and 3 kV. General technical conditions "and study Table 19" Permissible current loads of cables with copper conductors insulated from PVC compounds and polymer compositions that do not contain halogens ".

Where did the myth come from that sockets can only be connected with a 2.5 mm² cable

As you can see, the 1.5 mm² cable is designed for currents up to 21 A.

So where did the myth come from that "it will not withstand", and why a 2.5 mm² cable is pulled to sockets with a maximum current of 16A from a 16A circuit breaker, which, according to the same table, can withstand 27 amperes?

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It's simple. Once the director of a cable association told me about the origin of this myth.

In the 90s, almost all cables on the market were "Silent" - made not according to GOST, but according to TU. They had a very low cross-section of the veins. And the cable, on which it was written 1.5 mm², was actually less than one, and the cable with the proud inscription of 2.5 mm² had a real cross-section of about 1.5 mm². It was then that an unspoken law was born, which is still observed by almost all electricians: "the 1.5 cable is only suitable for light, and the sockets must be connected with a 2.5 cable". Indeed, when the cable has a false cross-section, it is better to overdrive.

Now on the markets you can still find a cable "made according to TU" with an underestimated cross-section, but in in large chain stores, almost all of the GOST cable and its cross-section lived close to nominal.

There are three myths why sockets supposedly cannot be connected with a 1.5 mm² cable:

Myth No. 1 "The thermal release of a 16 A machine should trip in less than an hour at a current of 23.2 A (1.45x of the nominal) and in an hour or more at a current of 18 A (1.13x of the nominal)".

In the same table, we see that a 1.5 mm² cable can withstand a current of 21 A for a long time.

From 23.2 A for an hour, nothing terrible will happen to it either, it just warms up a little more. In my experiment (https://ammo1.livejournal.com/1150202.html ), the VVG 3x1.5 cable withstood a current of 31.5 A, and at a current of 24 A, the cable sheath temperature in air was 49 °, and in the corrugation, 67 °. For VVG cable, the long-term permissible temperature is 70 °, the temperature in overload mode is up to 90 ° C.

Myth number 2. "The resistance of the 1.5mm² cable is so high that there will be a large voltage drop on a long cable under heavy load."

Let's calculate for the most extreme situation: cable 50 meters, load 16 amperes. According to GOST 22483-2012, the resistance of a kilometer of flexible copper conductors (Table 7) with a cross section of 1.5 mm² should be no more than 13.3 ohms, respectively, two conductors of 50 meters each 1.33 ohms. A resistive load that draws 16 A from 230 V has a resistance of 14.375 Ohm. The ratio of the resistance of the load and the cable is 1x10.8, respectively, 19.5 volts will drop on the cable. In real life, the cable is usually shorter and the load is less, so the drop is likely to be a few volts.

Myth number 3. "If the cable is long, the machine may not work in the event of a short circuit."

Again, we take 50 meters and, accordingly, 1.33 ohms. 230 / 1.33 = 172.9 A.
The electromagnetic release of the C16 circuit breaker will trip at a current exceeding the nominal 5 times (80 A) for more than 0.1 s, and at a current exceeding the nominal 10 times (160 A), it is guaranteed to shut down in 0.1 from.

Of course, there is nothing wrong with the fact that the sockets are connected with a thicker cable "with a margin", but I connect all the sockets with a 1.5 mm² cable, and you see for yourself.

© 2021, Alexey Nadezhin

For ten years I have been writing every day about technology, discounts, places of interest and events. Read my blog on the site ammo1.ru, in LJ, Zen, Mirtesen, Telegram .
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