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Electrosafe private residential building and cottage. Part 1
Dear Reader! It is necessary to recognize the fact that in the private residential sector and especially in cottages there is an extremely unfavorable situation in terms of electrical and fire safety. Violations are of a large-scale nature.
Especially depressing is the fact that both professional electricians and electrical engineers themselves sometimes do not understand and do not know certain provisions of the EMP and other regulatory documents. The purpose of this article is to help both electricians and homeowners correctly perform certain tasks.
Electrical Engineer S. Mironov post office
Consider all the dangers that may lie in wait for people and the house from electricity.
1. Direct contact with the human phase.
2. Short circuit (short circuit) between phase and zero.
3. Damage to the insulation of the phase wire with its subsequent closure on the metal casing of the electrical installation (on the HRE - open conductive parts).
4. The appearance at the entrance to the house of increased voltage (up to 380V) as a result of an accident on overhead lines (overhead line).
5. High potential drift from the ground through metal sewage pipes, water and gas supply and other HRC (third-party conductive parts).
6. Direct lightning strike into the house.
7. High potential drift along overhead lines to the house during thunderstorms.
In this paper, we consider the first four cases. In fig. 1 - 8 show 54 possible options for a person to get under voltage, which under certain circumstances can lead to electrical injury. Some of them are essentially the same, but we will not combine them for the sake of clarity.
Fig. 1 - 8 download in the archive from this link - https://i.electricianexp.com/en/elgildom1-8.zip (0, 6 mb)
So, we have a residential building, which, as a rule, is powered from the overhead line and in which there are no third-party conductive parts (HFC), and from electrical appliances - only AB (circuit breaker), a pair of sockets and a lamp. A familiar situation, isn't it? The number of emergency situations in this case will be three. The first of them is when a person touched a phase wire with his hand (see, Fig. 3 No. 18). Possible here fatal electrical injury.
The second emergency situation is when an overvoltage (up to 380v) from the overhead line came to the house as a result of an accident on the line. This will immediately cause the lights to burn out. The glass bulb of the lamp may explode, followed by spraying a red-hot spiral on combustible substances, which can lead to a fire. This will not happen if the bulb is in the protective lampshade. Well, the third case is a short circuit in the wiring. Here the AB should work, which will turn off the house.
What countermeasures can be taken here? In the first case, you with a 95% probability can save RCD (residual current device). True, you can be shocked by this. In the second case - set on input voltage monitoring relaywhich, when exceeding the voltage at the entrance to the house more than 240V, will turn off the power in the house. In the third case, as I wrote, AB will help out (if it is correctly selected).
Move on. Connect to the outlet, for example, a refrigerator. Then emergency No. 15 will be added. But if we, as before, installed an RCD, then we will eliminate this problem. True, at the same time you can be shocked, but with a probability of 95% you will survive.
Move on. Near the refrigerator, within the reach of a person’s hands, you have put some more electrical appliance with open conductive parts (HRE). Then emergency situations No. 1 and 8 are added. If there is an RCD, then you will be shocked by the current, and with a probability of 95% you will remain alive. Do not forget that at any moment up to 380V voltage may appear at the entrance to the house, and if you have not installed an ILV relay, your refrigerator and a nearby electrical appliance may burn out and even ignite, which will lead to a fire in the house.
Move on. Hurray, finally a metal water pipe was brought into your house. That is, now you have in your house HRO (third-party conductive part). This will add to you emergency No. 21 and No. 27 (for example, let it be a washing machine near a water tap).Further, if the phase gets into this HFC, then you will get emergency situations No. 15, 16, 22. In general, the situation as various electrical appliances and the HFC are installed at home can become very complicated, as can be seen from Figures 2-8.
So you came to a well-founded conclusion: why the hell do I need all this? Each time to think - will shake? Kill? Fire? The problem must be solved radically! What choice is there? According to the EMP, make in a residential building power supply system TN –C – S or TT. And which one to choose? According to the PUE, if it is not possible to ensure electrical safety in the TN - C –S system, then the TT system should be made.
What ensures the electrical safety of the TN - C - S system?
All protection in the TN - C– S system is based on tripping circuit breaker (AB) due to high short-circuit currents to the PE conductor. Hence the high quality and reliability requirements for PE and PEN conductors, through which communication with the power source is carried out. Now many experts are inclined to believe that if the overhead line from the transformer substation is completed self-supporting insulated wires (SIP), it can be argued that we have a “high-quality” PEN conductor.
This implies the fact that in case of damage to the wiring of the overhead line made by the self-supporting insulated wire, if it breaks, then all conductors, both phase and PEN wires, break at once. If the overhead line is made with single-core wires, then if it is damaged, the probability of breaking only the PEN wire is very high. In this case (a break in the PEN-wire on the line) at the inputs to residential buildings, the appearance of increased voltage (up to 380V) is possible, and the appearance of high-voltage electrical equipment on the HRE under certain circumstances.
That is, the TN - C – S system in this case does not provide the necessary level of electrical safety, and we, according to the EMP, must supply the residential building with the TT system. The differences between the TT system and the TN-C-S system can be seen from Fig. 9.
Fig. 9. Systems TT and TN-C
In the TT PEN system, the conductor is not divided into two conductors (into PE and N conductors) - in it it is used only as N wires, and the PE conductor is made already in place, by means of a charger (grounding device) near the house and from this the charger is taken PE conductors.
In the TN-C-S PEN system, the conductor is already used as both N and PE conductors, for which it is divided into PE and N wires at the PEN input of the wire into the house. In addition to this, the PEN wire is additionally grounded near the house to the pre-made charger (Re-ground the PEN wires).
So, we left the house on the street and looked at the overhead line from which our house is powered. If the overhead line itself (and not our branch to the input) is made by separate wires - everything, you need to do the TT system. If this is not the case, and the overhead line wiring is made by SIP, then you need to make sure that the SIP extends from the transformer substation to your house (that is, make sure that only the PEN wire is impossible to break from the TP to your house). If an overhead line with separate wires goes farther from the pole from which the entrance to your house was made, then this should not worry you (except if the line is not looped back, you need to make sure that this case is excluded).
So, we were convinced that from TP to your column there is a VL performed by SIP. Then you need to make the TN - C – S system. At the same time, do not forget that if the branch to the input to your house is made with separate wires, then replace them with SIP as well. (This is the best option).
And now let's see all the options in which a person can get an electric shock. These options are shown in fig. 1 - 8. There are 54 in total. Some of them are essentially the same, but for clarity, we will not combine them. How to eliminate them? To do this, according to the EMP, we must perform the BPCS (the basic system for equalizing potentials) according to paragraph 1.7.82. And if necessary - and DSP (additional system for equalizing potentials) according to clause 1.7.83.Along the way, we note that according to the PUE 7.1.88 for the bathroom and shower rooms, the PMP is mandatory.
If you perform a safety control system and a safety control system (that is, install jumpers between open conductive parts (HFC), between the HFC and third-party conductive parts (HFC) and ground the HFC and HRO, then when analyzing emergencies No. 1-17 and No. 19-54 (see Fig. 1 - 8) will be reduced only to step voltage (Uш> 0). The problem with step voltage is solved by performing a “high-quality” grounding device (GD) and equipping it in a “low pedestrian” place. at 30 mA.
Along the way, we note that when lightning strikes the ground, even far from your home through metal pipes of cold water, sewer pipes and gas supply can be drifted into the house of high voltage. Then cases No. 46, 47, 48, 51, 52 are probable. It is possible to get rid of such misfortunes only by installing insulating inserts on their entrance to the house that will prevent lightning from entering the house. But at the same time, all the HFCs that remained inside the house, we still need to connect the conductors to the shield PE bus (that is, ground again).
To summarize some of the results. All that we have done above is that we have fulfilled the requirements of the EMP for the creation of the Basic System for Equalizing Potentials and the Additional System for Equalizing Potentials, that is, we have eliminated almost all emergency situations (using the necessary jumpers, RCDs and ILV). There are problems with touch voltage and step voltage.
Step voltage problems are solved competently. grounding device (charger). Problems with touch voltage are solved by the correct selection and calculation of a circuit breaker (AB). With a correctly selected circuit breaker, the touch voltage lasts a very short time (0.4 sec at 220 V according to the PUE). It is believed that this is permissible under electrical safety conditions.
Clarification is needed at the end of this chapter. What is OSUP and PRSP.
OSUP is the Basic System of Equalization of Potentials. Why is it MANDATORY?
OSUP - this is the main guard of your home from the external environment. Everything metal that comes to your house from the outside carries a potential threat, because through these pieces of iron any current can penetrate the house and cause a lot of troubles. For example, a lightning strike into the ground, where a metal pipe of your water pipe is laid, even a kilometer away from you - and all lightning through this pipe will immediately jump into the house. Therefore, the main task of the OSUP is to send all these misfortunes to the ground right at their entrance to the house and not allow them to scatter around the house. To do this, all the iron entering the house directly at the entrance is connected to the OSUP and it, in turn, is connected to the ground.
In the TN-C-S system, the PEN conductor is also connected to the PSC conductor supplying your house with VL (they say that the PEN wire is re-grounded at the entrance to the house). Why is this done? Since the voltage on the PEN conductor should ideally always be zero, any increase in voltage on it during operation should be immediately eliminated, therefore, by connecting it to the ground, we achieve this.
Technically, the BPCS is done by performing Main Grounding Bus to which all the pieces of iron entering the house are connected, the PEN conductor of the power line and, of course, the grounding device itself. If there is a lightning conductor, then it is connected directly to the grounding device (there is nothing to go into the house for a moment of lightning). In a private residential building, the RE ground panel performs the role of the Main Grounding Bus.
Now let's talk about PRSP. While OSUP protects your house as a whole, DSUP protects only specific rooms in the house. In a residential building, something is constantly being rebuilt, repaired, and so on. At the same time, someone exchanges metal pipes for plastic pipes, someone does not, etc.
At the same time, many ties with the PMAS are lost somewhere deep in the house and it is impossible to track all these changes, therefore the EMP requires in the hazardous premises an ADDITIONAL CAPACITY BALANCING SYSTEM (DCMS). In residential buildings, bathtubs and showers are just such rooms.
In addition to the fact that the bathroom has pipes for water supply, sewage, heating and other third-party conductive parts (HFC), it can install various electrical appliances with open conductive parts (HRE) on which at any time there may be a phase from various malfunctions in these electrical appliances . The likelihood of electric trams here increases dramatically.
The objective of the DCMS is to prevent this. How can this be done? If we connect all the potentially dangerous pieces of iron in the bathroom together, here we connect all the potentially dangerous open conductive parts of electrical equipment (HRE) and stop there, we will face bitter disappointment. We got the result LOCAL potential equalization system which PUE forbids to do in a bathroom (PUE p.1.88).
What is the matter here? But the fact is that by combining all that is, we did not allow the current to flow if voltage appears on this LOCAL potential equalization system to drain into the ground. Having touched such a Local potential equalization system with your hand, the current will happily rush to the ground, but already through your body along the chain arm - legs - conductive floor - earth (hopes that it will drain down to any grounded third-party conductive part and the like should not be as at any moment these communications with the ground may be broken). The most reliable in such a situation is to fulfill the requirements of the PUE, that is, connect the local potential equalization system with a PE bus (count with the ground) of your shield with a separate conductor.
SO:
1. If the TN-C-S system is made in your house and there is a bathtub, then it is imperative to make a control system, while the control system must be connected to the solution at the entrance to the apartment (in your apartment panel)
2. The same if a TT system is installed in your home.
3. If two-wire wiring is made in your house (old housing stock), then you can’t make DCS. Such a DCS, not connected to the PE bus, is called a LOCAL potential equalization system, which the PUE forbids in clause 7.1.88 (the probability of skidding from the side of the potential in this case increases sharply, but there are no ways for it to drain). However, it is necessary to make a jumper between the metal body of the bathtub and the metal pipe supplying water to the bathtub (and if the supply pipe is made of plastic, with the tap itself). This will eliminate some emergency situations, but not all of the possible ones.
Fig. 10 Bathroom emergencies
Figure 10 shows that by installing such a jumper we reduced all possible emergency situations to only one when the current flows through the human body along the circuit: bath (metal pipe, faucet) - arm - legs - conductive floor - earth. This emergency situation can be eliminated only by making a grounding device (charger) and connect to it local potential equalization system (or going into the bath to wear rubber boots). The situation in the bathroom is even worse if a washing machine is installed.
Therefore, I recommend for those who have this situation immediately:
1. Install a jumper between the metal body of the bathtub and the metal water pipe (if the plastic pipe is by the tap itself).
2. Install an RCD of 30 mA at the entrance to the house.
3. Install the ILV relay at the entrance to the house.
This is something that can already be done right now, but will not save you from all emergency situations, so you still have to do the memory. After you make the memory, then perform the DCMS in the bathroom in its final form and the OSUP. Then you can find the time and remake the electrical wiring in the house on a 3-wire.
Very good recommendations on how to implement the DCMS, see appendices- Technical circular No. 23/2009 "on ensuring electrical safety and the implementation of the system of additional equalization of potentials in bathrooms, showers and plumbing." Along the way, pay attention to points 8 and 6 of this circular. From paragraph 8 it follows that if the water supply to the house is made of a plastic pipe that does not have a conductive insert connected to the OSUP, then the faucet in the bathroom should be considered an external conductive part (HFC) and it should be connected by a wire to the DSUP(even if it is mounted on a plastic pipe).
And further. In the bathroom, you can not arbitrarily install electrical appliances, sockets and the like.
Everything here is strictly regulated. Therefore, be sure to read the document that I gave in the appendix GOST R50571.11-96 `` Electrical installations of buildings. Part 7. Requirements for special electrical installations. Section 701. Bathrooms and Showers. "
And one more remark. Very often, a socket with a grounding contact is installed in the bathroom. In passing, I note that it should be installed in zone 3, that is, no closer than 0.6 m from the body of the bathtub. Since three wires go to such a socket - phase, zero and a protective PE conductor, which is connected to the shield panel, many, without further ado, connect the DCS to it using the grounding contact of the socket itself. DO NOT DO THIS. At any time, with a faulty outlet, your friend D. Vanya will come, who will remove the wire outlet, isolate it and tell you when you buy a new one, I will come and put it on.
He may simply not think about connecting any two wires to each other, that is, the DCSA will not be connected to the RE-bus of the shield with all the ensuing consequences, in addition, the protective conductor going to such a socket itself may be smaller section than required. Therefore, always connect the DCS to the shield guard with a SEPARATE conductor. Well, and the PE conductor itself, going to the outlet, can be left - there will be no harm from this.
Continuation of the article: Electrosafe private house and cottage. Part 2.
Applications:
Technical Circular No. 23/2009 "on ensuring electrical safety and the implementation of the system for additional equalization of potentials in bathrooms, showers and plumbing." - https://i.electricianexp.com/en/23_2009.zip
GOST R50571.11-96 '' Electrical installations of buildings. Part 7. Requirements for special electrical installations. Section 701. Bathrooms and showers "- https://i.electricianexp.com/en/R50571.11-96.zip
GOST R 50571.12-96 '' Electrical installations of buildings. Part 7. Requirements for special electrical installations. Section 703. Premises containing heaters for saunas "- https://i.electricianexp.com/en/R50571.12-96.zip
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