What is a TNC grounding system? What is the TN-CS grounding system? How to ground? When it comes to residential electrical installation, one of the equipments that generates more doubt is the shower, mainly about the grounding of the shower circuit. Where to connect the shower ground wire? Grounding the shower is one of the most common questions we encounter and it is about the correct connection of the electric shower grounding that we will talk about in this article, know which system to use and not use, understand all risks and see what the standard says about grounding, come on guys!
Shower grounding: How to do?
One of the most common questions is about using the shower ground together with the neutral, that is, in many cases, the grounded neutral is used for shower grounding, is that right?
The NBR5410 standard has an entire chapter dedicated to grounding, but even so for many electricians, grounding is still an extremely complicated subject. There are different types of earthing and the choice of earthing type determines what measures are to be taken to protect people from indirect contact.
Utilities demand that the neutral be grounded at the entrance of the installation and this idea of grounding the shower using the neutral comes precisely from the neutral being grounded by the concessionaire, making many electricians understand that it is the same thing, but it is not!
Grounding the shower directly from the neutral cable of the shower circuit itself characterizes the use of a TNC grounding system, this grounding system is prohibited for circuits with cables smaller than 10mm² and also for circuits of portable equipment. The standard makes it very clear that this grounding method should not be used.
Shower grounding: What are the risks?
The biggest risk of using the TNC grounding system is the loss of the neutral of the installation, in this case the phase cable loses the reference of neutral and both the neutral cable and the earth cable that are at this point, become a phase, that is, energizes the neutral cables to the broken point and as the earth cable inside the shower is in contact with the water, it starts to have direct potential and people who bathe in this situation may suffer an electric shock.
The resistance is basically a controlled short between phase and neutral. And when the neutral is broken, when the shower is turned on, all equipment connected to the grounding system will be energized. Therefore, the correct way of connection is a grounding cable coming from the frame ground bus to the shower, as shown in the image below.
There is a video on the World of Electrical channel that talks exclusively about this topic, showing in a very practical way why the TNC grounding system should not be used and as the standard makes this very clear, it is worth checking out!