Lightning protection is quite an important item in the electrical circuit of the house. If in an apartment building this is done by an organization serving the electrical network, then in a private housing stock you often have to take everything into your own hands. But before starting our story, we will try to consider in a very short form what lightning is and what it happens. M Lightning is a natural discharge of electricity.
1. Powerful vertical movements of air masses.
2. Sufficiently humid air.
3. Large vertical temperature gradient.
Lightning classification.
Development channel.
1. Downward-facing zippers.
2. Top-facing zippers.
By the nature of the charge.
1. Negative lightning (90%).
2. Positive lightning (10%).
Lightning consists of one or more strikes.
1. Short lightning strike up to 2ms.
2. Long lightning strike over 2ms.
So our introduction is over, as you have already noticed that we really tried to remind you of the baggage of school knowledge in a very short form. Well, now let's move on to our today's story.
Lightning protection.
Lightning protection can be internal and external. This is if you look into the depths of the issue, as if two security circuits, which, working in tandem with each other, can almost 100% secure your home.
External protection.
First of all, this is a lightning rod, which is always installed at the highest point of the house, connected by a conductor to your grounding system.
The task of the external lightning protection system is to catch and send it through the down conductors to the ground a fraction of a second earlier than the direct contact.
The lightning rod that is installed on the roof is usually of two types.
There is another option and it consists in the fact that a metal mesh is laid on the roof of your home, welded from reinforcement with a cross section of 8 - 10 sq. Mm, and with a cell pitch of usually 2 - 6 m.
But in principle, there is no particular difference between all these methods of lightning protection. Everyone has the same task - to catch the lightning discharge.
The cross section of the lightning rod should not be less than 12 sq. mm, but it is better, of course, that your lightning rod has a section margin. When installing the pin, you must always remember that it must rise above the highest point of the roof by at least 30 cm, the same applies to the cable receiver.
There is one more thing to keep in mind here. The zone protected by the lightning rod is approximately equal to its height. That is, at a height above the ground, for example, 8m, it will protect the territory of a circle with a radius of 8 meters from lightning. And below, we have tried to give you a series of schematic drawings of lightning rods and the zones that they can protect as an example.
Picture 1.
Figure 2.
Figure 3
It is better to take a wire through which the lightning energy will go to the grounding conductor with a steel section of at least 10 sq. mm or copper with a section of at least 6 sq. mm. Here, this is the case when the thicker the better. The conductor is connected to the receiver by welding or by bolting. The conductor must not pass metal elements closer than 30 cm.
Internal protection.
This type of protection is provided by special devices that are usually added to the circuit of the house shield and VU (input device). The essence of these special devices is as follows - suppose that lightning does not enter the house, but during a thunderstorm power surges occur quite often. This is because the electromagnetic field during a lightning strike can create pulsed currents in wiring and all kinds of devices.
The discharge does not have to hit the house - it can happen at a distance. But if, nevertheless, lightning hits the house, then in the best case, the lightning rod will drop the voltage into the ground electrode, but, in the worst case, the discharge will hit the electrical network of your house.
Even when lightning energy flows through the lightning rod, the current generated in the wiring can damage sensitive equipment. Well, with direct exposure, it’s better not to imagine what can happen. And here we would like to bring to your attention a rather interesting table - the methods of propagation of high-voltage atmospheric discharges.
Table 1. High-voltage atmospheric discharge. Distribution methods.
B. Category C restrictor.
There is also a category D restrictor. It looks exactly the same as the restrictors we presented in this image. As you can see, these devices in their appearance resemble ordinary circuit breakers, only without the shutdown lever. All you need to know about Surge Protectors (SPDs) is that they are installed between phase and ground or neutral and ground. The task of the limiters is to neutralize the overvoltage impulse.
In practice, three types of limiters are mainly used - B, C, D.
1. Class B - these limiters are installed in the course of the shield. They are designed to protect against ultra-high voltage or, in other words, a direct lightning strike.
2. Class C - devices are installed according to the scheme after class B surge arresters and serve as protection against induced currents.
3. Class D - is established when there are especially sensitive devices in your home.
All three types should always be used, because they have a different threshold of sensitivity, and set according to the scheme one after the other. OPN are calculated both for single-phase networks, and for three-phase.
Several schemes for connecting limiters:
Scheme 1. Connections of surge arresters, which are located between the input machine and the ground conductor, three-phase network.
Scheme 2. Connection of surge arresters, which are located between the input machine and the ground conductor, single-phase network.
Connection schemes:
Note. Remember that all diagrams are given for example. Everything can change when using a different type of equipment.
And finally, we would like to give you one, probably already boring advice. Don't skimp on protecting your home. And buy all the equipment from trusted sellers. And then no lightning will be afraid of you or your home.
Andrey Grekovich