How to check for grounding in sockets and measure its resistance with a tester

The modern house is full of electrical appliances. For their work to be efficient and safe, grounding is performed. This simple device will provide reliable protection for your home and people living in it from electric shock. In view of this, it is very important to understand the structure of the electrical system at home and what aspects should be paid attention to when checking its performance. So, for example, many home craftsmen are often interested in the question of how to check the grounding in the outlet in order to make sure that it works.

Why electrical appliances are grounded

The main purpose of the grounding circuit is to protect a person from electric shock. Although almost any serviceable equipment is safe in this regard, it is not insured against an emergency. An oil seal leaked in the washing machine or dishwasher, the protective sheath of the wire was frayed from vibration, the insulation on the electric motor or in the capacitor broke through.

In any of these cases, lethal voltages may be present on metal parts of electrical equipment. As soon as you touch the casing of the same washing machine, a current flows through the human body, the value of which, even at 60-100 mA, poses a threat to life. Almost every housewife is familiar with the situation when a washing machine or a meat grinder is “shocked”. This is at its best. At worst, it will simply kill.

But if the casing of an electrical device is connected to the ground in advance, then the emergency leakage voltage that appears on it will immediately go into the ground and will not be able to threaten the lives of people.

It is completely safe to touch faulty but grounded equipment.

Thus, by grounding an electrical appliance, you ensure the safety of both yourself and your loved ones. That is why checking the availability and quality of the ground loop in your home must be taken seriously.

Zeroing - false grounding

There is an opinion that by connecting the casing of the device to zero, you ensure its grounding. This opinion is completely wrong. Zero is indeed connected to the ground, but at best on a house board located tens of meters from your sockets. Since the neutral wire performs the functions of a power supply, the current of all consumers at home flows through it. Any wire has resistance, a voltage drop of tens of volts can occur between zero in your outlet and ground.

Zero the household appliance and these volts will be on the casing of the appliance. In the event of a break in the neutral wire somewhere on the substation site - your apartment, phase through the consumer will "run over" to all the zero terminals of your sockets, and therefore to the cases of all nullified electrical appliances. Here, in general, the whole apartment turns into a solid electric chair. Input: a grounded device is much more dangerous than its ungrounded counterpart.

If the neutral wire breaks, all the chassis of the neutralized devices are energized.

Ways to check the grounding in the socket

The safety of people depends on the presence of grounding in your house, therefore it is extremely important to know the state of the grounding circuit in the apartment and whether it exists at all. Everything the control work that will have to be carried out in this regard can be reduced to three points:

1. Visual inspection.
2. Indirect measurements.
3. Direct measurements.
4. Load tests.

Inspection by visual inspection

First of all, you will have to disassemble all the sockets. They must have an appropriate terminal to which the grounding conductor is connected, as a rule, it has a yellow-green color design. If all of these are present, then the outlet is grounded. If you find only two wires - brown and blue (phase and zero), then the outlet does not have a protective ground.

Such a scheme is extremely dangerous and with this inclusion one more threat is added. It is enough to swap the phase and zero at the input to the house or apartment (during repair work, anything can happen), as all the grounding terminals in the sockets will be energized. If you find such a mess in the outlets, stop it immediately. Ideally, the insides of the outlet should look like this: three wires are connected - phase, zero and ground.

If everything is in order with the sockets, look into the floor panel. The entrance to your apartment must also have three wires, and the ground must be securely screwed directly to the metal chassis of the switchboard or to the bus that is electrically connected to it. If everything is so, then we can assume that the visual inspection is over, since all floor panels must be connected to the grounding house circuit.

Indirect measurement verification

Unfortunately, the visual method cannot give one hundred percent guarantee. Any of the following reasons will nullify all inspection results:

1. "The shield must be grounded" and "the shield must be grounded" are far from the same thing. There are also hackers among professional electricians.
2. You can simply make the mistake of mistaking, for example, the nulling bus in the shield for the grounding bus.
3. Visually, everything is in order, but the grounding circuit of the house somewhere in the basement was cut down long ago and handed over to scrap metal.
4. You simply could not understand the jumble of panel wires, especially if the equipment is old, and the "experts" in electrical equipment in the house - in every apartment.

Therefore, you will have to become an electrician for a while. At this stage of verification, you will need a voltage indicator (screwdriver indicator) and a conventional AC voltmeter with a measurement limit of at least 500 V. For example, a Chinese tester (multimeter) will do.

The voltage in the house's electrical network can be measured with an ordinary tester set to the appropriate measurement limit.

Using the pointer, find the phase in the socket and make sure that there is no voltage at the other terminals, including the grounding one. Now load the home power grid by plugging in a 1-2 kW consumer into any of the outlets. Measure the voltage between the points phase - zero and phase - earth contact. Do not forget to set the required limit on the device before starting the measurement! The voltages should differ slightly (up to a maximum of 10 V) from each other, since the neutral wire is supplying and under load, and the ground wire is not.

If the voltages are absolutely equal, then, most likely, the grounding terminal is connected to zero either somewhere in the apartment junction boxes, or in the floor panel. In any case, you will have to find out where and why this was done. If the neutral and ground wires are simply connected to each other, then it's okay. It is much worse if the ground wire is connected to the null bus and not to the ground loop. In this case, it only depicts the grounding one, but, in fact, is the zeroing one. Of course, this problem will have to be fixed.

If the voltage spread is more than 10-15 V, then this means that the resistance of the grounding loop is too high and it must be considered faulty.

An option is also possible when there is no voltage at all between the phase and the grounding terminal. This indicates that the ground wire is either missing (checked visually), or not connected to the loop, or cut off somewhere in the wall or junction box.

Loop Resistance Measurement

This method, unfortunately, not only requires special equipment, but is also difficult to implement in high-rise buildings. But he is the most reliable. Its essence is to measure the resistance between the ground terminal of your outlets and real ground. To carry out the work, you will need a high-precision bridge ohmmeter and a huge number of wires. Checking the grounding with a multimeter in this case, alas, is impossible - not the same accuracy.

If you have access to such equipment, then get three wires of any size. One wire should connect the device and the grounding pin of the socket (it should be as short as possible). Two more - the device and metal pins from the kit, driven into the ground at a distance of 5-10 m from each other.

Depending on the voltage in your network meter readings must not exceed the following values:

• single-phase 127 V or three-phase 220 V - 8 ohms;
• single-phase 220 V or three-phase 380 V - 4 ohms;
• single-phase 380 V or three-phase 660 V - 2 ohms.

Load test

If you do not have a bridge ohmmeter or you live in a high-rise building on the last floors, then you can test the circuit by loading. This method is quite simple, but quite reliable. To carry out the test, you will need an electrical appliance with a power of at least 1 kW (iron, electric kettle, electric stove, etc.) ), voltage indicator (indicator) and AC voltmeter (tester). If you do not have a tester at your disposal, you can use a test lamp for a voltage of 220 V and a power of up to 100 W. It is not difficult to make it out of ordinary lighting.

Homemade warning lamp

Now let's see how to check grounding with a load tester. Measure the voltage between the phase and grounding terminals of the socket, write down the readings. Connect a heating device in parallel with the voltmeter. In this case, the voltage should drop by no more than 10 V. If you do not have a voltmeter at your disposal, then use a test lamp. When the load is connected, the brightness of its glow should decrease very slightly. The heating device itself during the tests will work as it should - it will fully heat up. A large voltage drop under load indicates that the circuit has too much resistance and should be considered faulty.

If your apartment is equipped with one or another leakage current protection device - differential circuit breakers or RCDs - then this test method will not work. The protection will take the current of the load connected to the grounding terminal as a leakage current and cut off the voltage in an emergency. On the one hand, the operation of the RCD will confirm that it is grounding in your house, and not zeroing, but on the other - you never know if the circuit will be able to withstand the short-circuit current in the event of a serious accident.

However, if you have a protection that works perfectly even against a leakage current, it will disconnect the emergency circuit even before the short-circuit current becomes critical. But if you still want to carry out a full-fledged loop test under load, then the protection devices will have to be temporarily disabled.

All switching and measurements must be carried out in compliance with electrical safety rules and under the supervision of a second person who is not involved in the work. Household voltage is life-threatening!