How to Install TT Earthing in the Frame Correctly.
Complete thread-by-thread assembly of the general electrical panel with all protections using TT grounding. The TT scheme has a directly grounded supply point, with the installation masses connected to grounding electrodes that are electrically different from the supply grounding electrode. This system is the most efficient in many cases.
Look... if you think grounding is a simple thing, I'm sorry to tell you that it won't always be like that. A poorly done grounding puts your installation at risk, even more so when it comes to TT grounding, the type of grounding that causes many discussions among professionals in our area.
Now if you still don't know what a TT grounding is and/or you also don't know that the way to connect DPS in this grounding scheme is different from the other schemes, you have to stay with me until the end of this class, because I prepared a complete explanation and ball show so you can understand once and for all.
First of all, let's name a spade: What is TT grounding anyway?
Well, in short, the TT grounding (or TT scheme if you prefer) is the one in which the equipment is grounded with its own rod, different from the rod used to ground the neutral, that is, in this scheme the points are not equipotential.
As I said, it causes a lot of discussions. And the fault of many of these discussions is the NBR-5410 standard itself, which in some points contradicts itself, as for example, in item 5.1.2.2.3.3 mentions that “All the mass s of the installation located in the same building must be linked to the main equipotentialization of the building.
Then I always asked myself, if that's the case, how is a grounding that is not equipotential allowed? Remembering the norm mentions about TT grounding, but anyway, we are not here to question the norm, despite these contradictions, we must follow what it determines, right?
But there it is, if you opt for a TT ground, that is to say that it is not connected to the neutral at some point in the electrical supply, the way of connecting the SPD changes, here comes the first doubt of many electricians:
WHERE TO INSTALL DPS? BEFORE OR AFTER THE DR?
Well, item 6.3.5.2.2 of NBR 5410 mentions that the DPS's must be installed as close as possible to the entry point, HOWEVER, they must be arranged as shown in figure 13.
let's see what he's talking about in that figure 13
“Does the electrical power line that reaches the building include the neutral?”. YES
"Is the neutral grounded on the building's main equipotential bus?".
Most buildings do not have this bus, so let's go the NO way. Notice that there is a lowercase letter c, let's see what it says:
- The hypothesis configures three possibilities of grounding scheme: TT (with neutral), IT with neutral and the line that enters the building already in TN S scheme.
following we see that there are 2 possible connection schemes. But notice that we have a letter again, this time the lowercase d. Let's see what she says:
There are situations in which one of the two schemes becomes MANDATORY, such as the case listed in item b) of 6.3.5.2.6.
AND WHAT MENTIONS THIS ITEM?
“ when the SPDs are installed, as indicated in 6.3.5.2.1, next to the entry point of the electrical line in the building or in the main distribution board, as close as possible to the entry point, and the installation is provided with one or more DR devices, the SPD can be positioned upstream or downstream of the DR device(s), subject to the following conditions:
when the installation is TT and the SPD are positioned upstream of the DR device(s), the SPD must be connected according to diagram 3 (see figure 13);
Oops! in this case then we must MANDATORILY adopt scheme 3 of figure 13!
In practice, it will look like this:
Here we have a practical QDC, with the earth and neutral buses, and we are going to add the protection devices, 3 DPS (two phases plus neutral), a bipolar generator circuit breaker and a four-pole DR for illustrative purposes only.
How to Install TT Earthing in the Frame Correctly.
Complete thread-by-thread assembly of the general electrical panel with all protections using TT grounding. The TT scheme has a directly grounded supply point, with the installation masses connected to grounding electrodes that are electrically different from the supply grounding electrode. This system is the most efficient in many cases.
Look... if you think grounding is a simple thing, I'm sorry to tell you that it won't always be like that. A poorly done grounding puts your installation at risk, even more so when it comes to TT grounding, the type of grounding that causes many discussions among professionals in our area.
Now if you still don't know what a TT grounding is and/or you also don't know that the way to connect DPS in this grounding scheme is different from the other schemes, you have to stay with me until the end of this class, because I prepared a complete explanation and ball show so you can understand once and for all.
First of all, let's name a spade: What is TT grounding anyway?
Well, in short, the TT grounding (or TT scheme if you prefer) is the one in which the equipment is grounded with its own rod, different from the rod used to ground the neutral, that is, in this scheme the points are not equipotential.
As I said, it causes a lot of discussions. And the fault of many of these discussions is the NBR-5410 standard itself, which in some points contradicts itself, as for example, in item 5.1.2.2.3.3 mentions that “All the mass s of the installation located in the same building must be linked to the main equipotentialization of the building.
Then I always asked myself, if that's the case, how is a grounding that is not equipotential allowed? Remembering the norm mentions about TT grounding, but anyway, we are not here to question the norm, despite these contradictions, we must follow what it determines, right?
But there it is, if you opt for a TT ground, that is to say that it is not connected to the neutral at some point in the electrical supply, the way of connecting the SPD changes, here comes the first doubt of many electricians:
WHERE TO INSTALL DPS? BEFORE OR AFTER THE DR?
Well, item 6.3.5.2.2 of NBR 5410 mentions that the DPS's must be installed as close as possible to the entry point, HOWEVER, they must be arranged as shown in figure 13.
let's see what he's talking about in that figure 13
“Does the electrical power line that reaches the building include the neutral?”. YES
"Is the neutral grounded on the building's main equipotential bus?".
Most buildings do not have this bus, so let's go the NO way. Notice that there is a lowercase letter c, let's see what it says:
- The hypothesis configures three possibilities of grounding scheme: TT (with neutral), IT with neutral and the line that enters the building already in TN S scheme.
following we see that there are 2 possible connection schemes. But notice that we have a letter again, this time the lowercase d. Let's see what she says:
There are situations in which one of the two schemes becomes MANDATORY, such as the case listed in item b) of 6.3.5.2.6.
AND WHAT MENTIONS THIS ITEM?
“ when the SPDs are installed, as indicated in 6.3.5.2.1, next to the entry point of the electrical line in the building or in the main distribution board, as close as possible to the entry point, and the installation is provided with one or more DR devices, the SPD can be positioned upstream or downstream of the DR device(s), subject to the following conditions:
when the installation is TT and the SPD are positioned upstream of the DR device(s), the SPD must be connected according to diagram 3 (see figure 13);
Oops! in this case then we must MANDATORILY adopt scheme 3 of figure 13!
In practice, it will look like this:
Here we have a practical QDC, with the earth and neutral buses, and we are going to add the protection devices, 3 DPS (two phases plus neutral), a bipolar generator circuit breaker and a four-pole DR for illustrative purposes only.
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