Is shower wire thinner than the installation, why?



Have you ever wondered why the wire in the shower is thin and the installation is thick? This is that doubt that takes the sleep of many electricians because in the shower body the manufacturers instruct us on the minimum wiring required, and in the shower, the connection cables are thinner? Today’s article will explain everything about this subject and provide the answer to this very common question.

Let’s first understand this wiring better, the 3 wires in the shower are phase cable, neutral cable and ground cable. The shower is made with thinner wire than the installation wire, this is normal and does not mean that your shower is defective. The dimensioning of the internal cables depends on the electrical power of that electric shower, that is, the electric shower 110V and 220V are installed with different cables.

Electric shower: Technical information

When analyzing the body of a shower it is possible to see the technical information of that shower recorded, including the minimum cable section of the electrical installation to connect this shower. This information must be written on the shower body as required by the NBR 12483 standard, which deals with electric showers. The example that we are going to use in this article is a 127V voltage shower, 5400W power, 43A electric current and the frequency can be 50 or 60Hz. Below is the minimum cable section to be used for installation, which in the case of this shower is 10mm², as shown in the image below.

Example of technical information engraved on the shower body

Electric shower: Cable dimensioning

And then the question arises, why do I have to use a cable of at least 10mm² to install this shower, and the shower cable itself is 6mm². When the electrician thinks about cable dimensioning, he soon uses the NBR 5410 standard that deals with cable and wire dimensioning for the electrical installation, but a point that many are not aware of, is that the NBR 5410 standard does not deal with cable dimensioning. and wires for equipment for use that have their own standard, and the shower is one of that equipment that has its own standard. NBR 5410 makes this very clear in item 1.2.2, in washer c), which says that this standard applies to all wiring and all electrical lines that are not covered by the standards relating to the equipment in use.

Even if we think about the dimensioning following the NBR 5410 standard, the thinnest cable in the shower is justified, because the cables of the shower body are not inside a conduit, in fact they are exposed and protected by a PVC conduit. So, if we think about the shower in our example, it needs a cable that supports at least 43A! Observing the installation method of this cable by table 33, it can be classified as exposed cable and without any protection, therefore, fitting in method 15. Following in table 33, we must observe the unipolar cables or multipolar cable away (s) from the wall more than 0.3 times the cable diameter, which is the case in our example. This installation method takes us to the reference method F for unipolar cables, as shown in the following image.

Example of electrical installation method

Now let’s see table 38 for cables with PVC insulation, conductor temperature of 70 ° C and ambient reference temperature of 30 ° C. We must analyze the column of method F for two charged cables, after all the shower is a phase and neutral. So we can see that the value that comes closest to more is 53A, as shown in the image below. Following the line, we can see that the cable to be used is 6mm², which matches the manufacturer’s cable.

Electrical installation reference method example

Continuing with the proper sizing method, no correction factor will be applied as it does not have an conduit occupancy rate, and as the distance of the section is short, it does not cause a significant voltage drop. There is also no temperature correction factor considering that the exposed cable is cooled by air.

This shows that even using the dimensioning of the NBR5 410 standard, the thinner cable is justified and at this point, we can still think about the material savings for the manufacturer, who like it or not, can somehow impact the final price of this product for the customer, even if the difference is very small.

So we end this article with an explanation and answer as to why the electrical cable for the shower manufacture has a smaller section than the installation cable that connects the shower. If you still have any questions, leave in the comments that we will be happy to answer.