Grounding the ventilation system: rules and subtleties of the protective circuit device
Have you ever experienced electric shocks when touching metal housings of home appliances? One of the reasons for the threat of electric shock is the absence or improper grounding of the ventilation system in a private house. Its device is required for the safe use of electrical equipment.
Agree that even weak impulses do not cause positive emotions. And in people with pacemakers, the effects of such touches can be especially sad.
Checking the correctness and integrity of grounding is not difficult. You should not invite electricians very often for this. We will help you to get a deeper understanding of all the intricacies of electrical safety control of a home ventilation system.
The content of the article:
- The physical nature of the grounding process
- What does grounding consist of?
- Classification and types of grounding
- Differences between the protective and working systems
- How to make grounding ducts?
- Installation of grounding conductor protective circuit
- Common homemaker mistakes
- System Check by Technical Services
- Why ground ducts?
- Conclusions and useful video on the topic
The physical nature of the grounding process
Beautifully installed and cleaned into walls or channels, the wiring, as well as the complete absence of electrical devices in the ventilation system, does not guarantee injury from contact with its metal parts. Only a reliable connection of the conductive external structures of the ventilation equipment with grounding will provide you with confidence in safety.
Parts of air ducts, fan housings made of metal and other electrically conductive materials that are not in live mode are to be grounded. Such requirements are spelled out in the Electrical Installation Rules (PUE).
An electrical charge on accessible touch elements may result from damage to the insulation of nearby wires, appliances, or static electricity. Grounding means that if a random charge occurs, it will leak from the duct into the ground.
From the school course in physics, we all know that electric current follows the path of least resistance. If we compare, for example, with the free flow of accidentally spilled water, the analogy is this: the water will not flow upward or sideways, but will rush down according to the force of gravity. So with an electric charge, accidentally hitting a grounded duct, it leaks deep into the ground to the grounding loops of the house circuit.
The electrical conductivity of a person can be reduced by additional insulation from earth and other electrical conductors. To do this, use special protective clothing, shoes. And you can increase it, due to the moist unprotected area of the skin.
A person with a built-in metal medical device is at greater risk. Or hung with various metal ornaments. Still current resistance is reduced in people intoxicated.
What does grounding consist of?
The ground loop is a simple circuit of two elements - conductors and grounding conductors.
Throughout the ducts located inside and outside the house, their external electrically conductive parts, which are not under normal operating conditions, must be connected to a single electrical circuit. At at least two points, this bundle is firmly attached to the ground loop.
Grounding the ventilation ducts is necessary in accordance with the regulations of the EMP. The rules require the use of steel strips, copper wires or direct connection with grounded pipelines, other structural elements. It is usually customary to combine grounding of ducts with a common grounding system at home.
Classification and types of grounding
These elements ground loop any type are directly in the ground. Grounding ensures that electric charge flows into the ground from the enclosures and other non-working conductive parts of ventilation equipment.
Earthing switches are of two types - natural and artificial. According to the PUE standards, it is preferable to use natural grounding conductors.
In a private house, these include:
- metal pipelines, power cable armor;
- buried reinforced concrete columns, foundations;
- metal street structures, for example, a fence.
It is forbidden to use water and sewer pipes as natural grounding conductors.
Before joining the permitted types of natural grounding conductors, their conductivity should be determined. The provisions of the PUE regulate the maximum value of the resistance to spreading of grounding conductors. For sources of three-phase / single-phase current voltage of 380 / 220V, its value should be no more than 4 Ohms.
To order measurements, you need to contact any certified electric laboratory. You should be given a protocol with the result of measurements and copies of certified documents certifying the admission of specialists, the compliance of the devices with metrological requirements.
Differences between the protective and working systems
Grounding conductors from air ducts can be connected to the main grounding bus (GZSh) or to the protective grounding bus in the electrical panels. Provided that this equipment is available in the house where, if necessary, the ground loop is already installed.
If you have already decided which air ducts in the house must be earthed according to the rules, then do not confuse the connection points. The fact is that in the electrical panels there is a working grounding bus. It is intended for a working function, not a protective one.
The working neutral conductor (N) is the fourth residential supply power cable, where there are three phase wires (L). It is associated with a neutral power source. In the electrical panel, this neutral conductor is connected to the shield body and the working ground bus.
There are cables with a special insulated conductive braid, armor, which can serve as a natural ground electrode. Or with a protective earth conductor (PE).
It also connects to the shield body and to another grounding bus, but not working, but protective. It is not a fact that in your house such a reinforced expensive cable is used in the power supply circuit.
Using a working neutral conductor, all devices with a voltage of 220 V are connected to the power supply. That is, there are two contacts “phase” and “zero” in the socket. All home craftsmen are aware of this.
In euro socket models there is still a grounding contact. You should never confuse these two completely different concepts - grounding and grounding. The consequences can be sad for the victim, and for the owner of a private house. After all, it is the homeowner who is responsible for the safe operation of all equipment.
How to make grounding ducts?
Between the flanges, it is necessary to mount flexible copper shunt jumpers, if there are no factory ones on the air ducts. A bolted connection, even made without insulating gaskets, is unlikely to comply with the rules.
Since the contact transition resistance must be less than 0.1 Ohm. It is allowed to join the joints of metal structures by welding steel brackets.
Grounding conductors are connected:
- through adapter busbars to bolts of flanges or other detachable connections;
- crimp clamp, cleaned and treated with conductive grease;
- by welding or reliable detachable connections to the supporting frame.
Visible grounding is necessary at the beginning and at the end of the duct. Copper tips can be used as adapter busbars.
The cross-section of steel grounding conductors must be at least 75 mm2. With a copper conductor, section thickness is allowed from 10 mm2.
Ground the conductive parts of the fan enclosures with a circuit with separate conductors. Serial connection of fans with grounding of air ducts is not allowed, there should only be a parallel circuit.
Installation of grounding conductor protective circuit
During the reconstruction or construction of a private house, the missing grounding device can also be done with your own hands. The effectiveness of the circuit depends on the selected connection scheme, type and resistivity of the soil.
The resistance of the grounding device, used solely to protect a person from being struck by static electricity from the duct, can be increased to 100 Ohms. Introduces resistance measurement methods next article, which we recommend reading.
It is advisable to photograph all stages of hidden work during the installation of the grounding loop.Printed paper photographs, freehand drawn diagrams with exact dimensions and indicated materials, keep together with test reports.
These are serious documents called the passport of the grounding device. With their help, you can control circuit changes, plan repairs and even reduce the tariffs of the insurance company when applying for a home policy.
Common homemaker mistakes
Self-grounding can be performed flawlessly. But sometimes inattention, haste, low practical skills lead to errors in installation.
The most common common flaws and flaws:
- Weak contact due to the protective coating of detachable joints;
- Non-compliance with the standards for the size of grounding conductors;
- Quickly collapsing material of the elements of the grounding system;
- Connection of zero working and protective conductors.
For some reason, many are advised to have earthing switches away from home, choosing distance figures from the depths of their consciousness. All installation data are advisory, but not mandatory. The circuit does not pose any danger to humans; there are no restrictions in the rules on distance.
Some "experts" advise to pour salt into the ground to ground electrodes for better conductivity. No need to listen to amateurs, consult with professionals.
Indeed, in the beginning, due to an increase in humidity, a slight decrease in the resistance to spreading of the ground loop is possible. But metal elements in such an environment will quickly collapse due to the acceleration of the corrosion processes of grounding conductors.
System Check by Technical Services
Inspecting the grounding of home ventilation equipment is recommended 2 times a year in spring and autumn. Detected breaks, corrosion, other defects of visible external connections must be fixed as soon as possible.
It is better to carry out measurements with the help of electricians in summer dry weather or in winter frosts. Under these conditions, the soil resistivity increases. And this means that the amount of resistance to spreading of the grounding loop will be maximum. That will ensure its reliability, compliance with the norm in all other seasons.
Why ground ducts?
Ignoring proper design and installation of grounding ventilation systems owners of private homes most often explain the reluctance to spend extra money. For some reason, people who do not have special knowledge in this field believe that electrical safety can be neglected here.
In Russia, electrical injuries cause death in 2.7% of accidents. Behind these dry numbers are concrete human victims. The bottom line is that electric current catches up unexpectedly. It has no smell, color, you will not see it and you will not feel it until you touch it or determine it with the help of devices.
The process of attaching metal parts of ventilation equipment to grounding devices requires special care. Observe safety measures when working at heights, with welding equipment, with electrical appliances.
Conclusions and useful video on the topic
Installation of the ground loop in a private house:
The composition of the exhaust ventilation system of the building:
The fan casing, air ducts and other elements that may be charged with electric power must be safe for accidental human contact.
All grounding conductors, electrodes, natural grounding conductors have electrical characteristics normalized by the rules. A well-designed circuit and correctly mounted protective elements will serve you for many years. It is only important to periodically carry out maintenance and measure the electrical parameters of the grounding parts.
And what do you think - is it worth it to do grounding on your own or is it better to invite specialists? In the form below for comments, share your opinion, ask questions to our expert, leave a review.