Today I will debunk the myth and tell you how it happened that almost all electricians connect sockets with a 2.5 mm² cable.
In the comments to my review of IKEA extension cords (https://ammo1.livejournal.com/1229112.html) often wrote the same thing: “One and a half squares will not withstand 16 amperes.”
We open GUEST 31996-2012 “Power cables with plastic insulation for a rated voltage of 0.66; 1 and 3 kV. General technical conditions” and study Table 19 “Permissible current loads for cables with copper conductors insulated with polyvinyl chloride plastic compounds and halogen-free polymer compositions.”
As you can see, the cable with 1.5 mm² cores is designed for currents up to 21 A.
So where did the myth come from that it “won’t stand it”, and why is a 2.5 mm² cable pulled to sockets with a maximum current of 16A from a 16A machine, which, according to the same table, can withstand 27 amperes?
Everything is 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 “TUSH” – made not according to GOST, but according to TU. They had a very underestimated cross section of the veins. And the cable on which 1.5 mm² was written was actually less than one, and the cable with the proud inscription 2.5 mm² had a real cross section of about 1.5 mm². It was then that the unspoken law was born, which almost all electricians still observe today: “a 1.5 cable is only suitable for light, and sockets must be connected with a 2.5 cable.” Indeed, when a cable with a false cross section, it is better to overdo it.
Now in the markets you can still find a cable “made according to specifications” with an underestimated cross section, but in large chain stores almost all the GOST cable and its cross section lived close to the nominal one.
There are three myths why sockets supposedly cannot be connected with a 1.5 mm² cable:
Myth #1 “A 16A circuit breaker thermal release should trip in less than an hour at 23.2A (1.45x rated) and an hour or more at 18A (1.13x rated).”
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 him either, it will just heat up a little more. In my experiment (https://ammo1.livejournal.com/1150202.html), the VVG 3×1.5 cable withstood a current of 31.5 A, and at a current of 24 A, the temperature of the cable sheath in air was 49°, and in the corrugation 67°. For the VVG cable, the long-term permissible temperature is 70°, the temperature in overload mode is up to 90°C.
Myth #2. “The cable resistance of 1.5 mm² 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 wires (Table 7) with a cross section of 1.5 mm² should be no more than 13.3 Ohm, respectively, two wires of 50 meters each 1.33 Ohm. A resistive load drawing 16 A from 230 V has a resistance of 14.375 ohms. The ratio of load and cable resistance is 1×10.8, respectively, 19.5 volts will drop on the cable. In real life, the cable is usually shorter and the load is smaller, so the drop is likely to be a few volts.
Myth #3. “If the cable is long, the machine may not work in case of a short circuit.”
Again, we take 50 meters and, accordingly, 1.33 ohms. 230/1.33=172.9A.
The electromagnetic release of the C16 circuit breaker at a current exceeding the rated value by 5 times (80 A) will turn off in more than 0.1 s, and at a current exceeding the rated value by 10 times (160 A) it will be guaranteed to turn off in 0.1 s.
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.
Peace for everyone!
© Alexey Nadezhin
For twelve years I have been writing about technology, discounts, interesting places and events. Read my blog site ammo1.ruin LiveJournal, Day, MirTensen, Telegram.
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