How to check the current cable cross section and why they need to do before you buy

There is no person who is not faced with the repair of the house. And often you and I have to buy a cable to lay new lines or change the wiring completely. And he came to the store, we call us the necessary section and wait until the dealer rewind the desired footage, and thus do not even think that purchased, e.g., VVG-P 3 * 2.5 mm2 can have a much smaller cross section, which means that it will withstand load less stated. This can bring very serious and unfortunate consequences.

In this article I will discuss in detail how to check the real cross section from the acquired cable with a micrometer, calipers, and the usual range with a screwdriver.

What is it for

You may well ask: Why do I need to do? And it is necessary for your own safety. Imagine this situation: you have decided to install a powerful boiler itself and for that mounted a separate line. In this case you use a cable, such as VVG 3 * 4 mm 2, as it is counting on such a section is quite allow a load of a boiler. But the real cross-section of wires 2.5 mm2, and it turned out it means that the wire is in the process will be heated, and if he is also poor insulation, the short circuit happens pretty soon and it is good if it will not come up fire.

Unpleasant is not it? And all because of the fact that the cable does not match the specs and you have not checked out before buying.

Why the manufacturer underestimates the real cross section

This happens because of the banal desire to earn more, which is why there is a "slimming" lived in the wire and the thinning of the insulating material. After all, if it is smaller, and the cost of such a wire is lower and thus profit from the sale of the above.

And in the end because of this, we suffer with you.

We check the actual cross section of the cable

So, before proceeding to the process of verification, let us recall the formula that we will need to get a result.

At first glance, the formula is cumbersome and inconvenient, but it is actually just for the convenience of you and give it in simple form:

S = 0.785 * D2

As you can see now we just need to substitute the measured diameter and calculate, so here we go:

Counting sectional monolithic core

For this calculation I were purchased brand cable VVG n 3 * 1.5 mm2, VVG n 2 * 1.5 MF 1 1.5 mm2, 2.5 mm2 MF 1, 3 PVA * 2.5 mm2 and OPV 3 * 2.5 mm2. For more accurate measurements I use a micrometer. But if you do not have this at hand, it is quite possible to manage and caliper.

VVG check n 3 * 1.5

So, we proceed to measurement. To produce a count, it is necessary to clean the wire insulation and wire diameter measured as shown in the picture

Next, we substitute the value obtained in the formula: S = 0.785 * (1.21) 2 = 1.149 mm2. As can be seen the obtained value is different from the stated 1.5 mm2

VVG check n 2 * 1.5

Now let's test our wire cable. The algorithm is the same.

The obtained value is substituted into formula S = 0.785 * (1.23) 2 = 1.187 mm2. And here we see an understatement section wires. But let's move on.

Check PPV 3 * 2.5

After stripping lived still produce count diameter with a micrometer, and then substitute the value obtained in our formula: S = 0.785 * (1,78) 2 = 2.48 mm2. Here we see that the claimed and actual conductor cross-section is the same.

Calibratable PV 1 1.5 *

Now test equipment wire

Counted by the formula: S = 0.785 * (1,22) 2 = 1.168 mm2. And then the obtained real sectional claimed below.

Check MF 1 * 2.5 mm2

Now we check the mounting heavy gauge wire

counts S = 0,785 * (1,57) 2 = 1.93 mm2. Again underestimated the real section of the conductor.

Check PVA 3 * 1.5

So now let's check the flex cable. Here, checks will be harder, but not much. We are with you still need to clean up the core of the isolation, then count the number of distinct veins in the wire and measure the diameter of a single strand.

So, we measured the diameter of a single strand, and it is equal to 0.26 mmFurther also calculate the formula section S = 0.785 * (0,26) 2 = 0.053066 mm. This is the value we received for one core, and now that number is multiplied by the number of wires and get the total cross-section of the conductor is 23 * .053066 = 1.22 mm2. As you can see, here we are also seeing an understatement of the real cross-section of the conductor.

And what to do if there is no measuring instruments

Even in the absence of instrumentation can calculate the cross-section. To do this, take any screwdriver to clean the core of the insulation and screw it on a screwdriver, and try to lay the coils tightly as possible.

Note. Winding more turns will give you the most accurate result.

Then we count the number of turns and length of the resulting helix and further by the formula

Perform the counting of the resulting diameter D = 21 mm / 16 = 1.31 mm2 windings. Now calculate the conductor cross-section: S = 0,785 * (1,31) 2 = 1.35 mm2. Cross section counted micrometer S = 0.785 * (1,31) 2 = 1,34 mm. The difference in the values ​​is due to an error. But both count still showed a low value of the declared by the manufacturer.

Conclusions and recommendations

This is how you can really count the cross section of the cable. But what to do if you have passed all the shops and found a really high quality cable manufactured in accordance with GOST. In this case, take the cable to one rated higher than, for example, you need a VVG 3 * 1.5 mm2, take VVG 3 * 2.5 mm2, need 3 * 4 mm2, take 3 * 6 mm2, etc. Thus, you will be able to withstand the required cross-section for your own posting.

Dear friends, I suggest in the comments to share their "records" section of underestimation lived in the cables.

Thank you for your valuable attention!