When and why is it necessary to apply repeated grounding?

When designing power supply system at the site of the consumer, the designers are planning grounding system on default. Grounding system is protection for people against electric shock arising in case of damage of electrical equipment and appliances. There are several variants of their execution, and we got a question from one of our readers about TN-C type of grounding.

Question: If TN-C system is already mounted in the house, is it necessary to install additional grounding?

Connection scheme in the system TN-C

Connection scheme in the system TN-C

To answer the question, let's recall about this grounding method. Some time ago, this system was widely used in apartment buildings, as well as in the networks of street lighting. The designation of letters TN-C means the union of functional and protective zero conductors, ie, neutral and protective conductor are combined into a single PEN conductor. PEN conductor connects the grounding contour, made in the transformer substation, giving power to the object with the consumer outlets, thus creating protective grounding. The advantage of the system is its simplicity and low cost of installation. The apparent disadvantage is a threat of an electric shock to people.

Answer: this system is outdated and needs to be changed. Paragraph 1.7.80 prohibits the use of RCDs in TN-C system, but since it is impossible to provide a proper electric safety without SRC, then this system turns out to be prohibited. TN-C system should be modified to TN-C-S, dividing the PEN-conductor into two conductors: N - zero and PE-protective. Since we are considering the case when the object is a single-family house, it is recommended to perform repeated grounding with the resistance less than 30 ohms in accordance with paragraph 1.7.103 EIC 7th ed, having mounted modular-rod grounding. Grounding device is made of copper-bonded metal rods, set into the ground, and combined with the PE-conductor.

In the modern world, person's life is unimaginable without electric devices, that is why,  it is important to provide electrical safety for you and your relatives. Call or email our technicians and they will calculate grounding configuration appropriate for your task!

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