Stray currents in simple words: what is it, measurement, protection against stray currents in water and gas pipes, heated towel rail, boiler, gas column

Бstray currents are the potential that appears in the earth when it is used as a conductor. With prolonged flow, it has a destructive force and negatively affects metal products in the soil or on its surface.

The appearance of stray currents is most likely near electrified vehicles, due to leakage on power lines or for other reasons.

Causes and sources of stray currents

If we talk about the sources themselves, there are several of them: electrified transport, power lines and even some household items.

What does a stray current look like – video.

Different types of transport

One of the main sources of stray currents are types of transport that run on electricity:

• trams;
• electric trains on the railway;
• transport used in quarries, mines and industry;
• metro etc.

The next cycle involves the passage of the potential through the wheels, and then to the rails and back to the traction substation.

When passing through the rails, the current encounters a certain resistance, which is why some structural elements have a potential. In the course of approaching the substation, it decreases to zero.

The current distribution diagram is shown below.

Where:

• a – contact wire, through which voltage is supplied to the power plant of electric transport;
• b – supply filler connected to the supply wire;
• c – one of the traction substations that feeds the electric transport networks;
• d – drainage filler, which is connected to the rails;
• e – rails;
• f – pipeline on the path of stray currents;
• g are positive potentials in the anode zone;
• h are negative potentials in the cathode zone.

The latter spread over the soil and damage everything that gets in the way:

• gas pipelines;
• metal constructions;
• water and sewer pipes;
• metal cable products, etc.

All metal elements with low resistivity fall under the “strike”. The parameter of the latter should be less than that of the soil.

Power line

Another source of stray currents can be power lines with isolated neutral. Most often, lines of 6, 10 and 35 kilovolts belong to this category.

Their peculiarity is the lack of grounding of the transformer neutral, which, in the event of one of the wires falling to the ground, does not lead to a short circuit and protection operation.

When such damage occurs, as a rule, automation is triggered, after which a team of workers goes to the facility to inspect and fix the problem.

In addition, stray currents near a fallen power line wire can lead to the appearance of step voltage.

In the event of a person approaching, a potential may appear between the soles of the feet, which can be fatal to life. That is why such situations should be eliminated as soon as possible.

Static electricity at home

You can’t relax in ordinary life either, because static electricity can accumulate on metal elements (batteries, plumbing, bathroom, etc.).

As a result, stray currents appear, which can damage the metal.

The cause of problems most often is the lack of grounding, errors in the installation of wiring along the riser, etc.

Effect on metal

The main disadvantage of stray currents is their negative effect on metal elements. Pipes, cable lines, reinforced concrete structures, etc. are at risk.

An additional factor, besides corrosion, is the appearance of leakage currents. This process accelerates destructive processes.

There are cases when the pipeline in the water supply system was destroyed under the influence of stray currents in two years with an official service life of at least 20 years.

Which facilities are most at risk?

A feature of stray currents is the difficulty of identifying and controlling, therefore, all metal underground structures are at risk.

The following structures are susceptible to corrosion:

1. Cables laid underground and having a sheath made of metal.
2. Metal pipelines. As already noted, stray currents in water pipes most quickly destroy the product and reduce the service life by almost ten times. This feature does not only apply to plumbing. Danger is also borne by stray currents in gas pipes and sewers.
3. Metal tracks for electric transport: railway, trams.
4. Elements of houses and other objects made of metal.
5. All-metal elements, for example, a tank for gasoline or diesel fuel.
6. Underground electric transport used in the creation of the subway.

Stray current measurements

The only way to determine the source of current input to earth is to make measurements.

Applied equipment:

1. Reference electrodes. Can be connecting or portable type. The main thing is that copper-sulphate technology should be the basis.
2. Digital multimeter.
3. Wire with reliable insulation. Length – not less than 100 m.

After receiving the information, you can quickly develop a set of measures and protect metal elements.

Measurements take place in several stages:

1. Resistance control between rails and ground.
2. Determination of the potential difference between metal elements underground and rails.
3. Analysis of probable electricity leaks from the cable line throughout its entire length.

In the process of measurements on the tracks, it is recommended to choose the period of the minimum frequency of traffic. As for the equipment, it must have a high accuracy class – at least 1,5.

Measurement parameters:

• lower resistance threshold – 1 MΩ;
• maximum potential difference – 10 mV;
• check time — 10 min;
• recording parameters – once every 10 seconds.

Stray current protection

All protection methods are conditionally divided into two types: passive and active. The former involve isolating pipes from the ground, while the latter involve the use of additional structures that require installation and electricity costs.

Let’s consider each of the protection options in more detail.

Passive

The most common option is the use of passive protection.

Basic options:

1. The use of insulating materials: electrical tape, special surface protection, bitumen. This method is used for plumbing structures. When performing work, you need to act carefully, because with mechanical damage to the metal, corrosion can accelerate.
2. Spacing pipes or cable lines to a greater distance. Such work is best done at the design stage. The same method applies to electric transport lines, the distance between which also needs to be increased.
3. Replacement of elements from metal to plastic. In this case, the equipment leaves the risk zone and does not respond to existing stray currents. This is due to the absence of electrochemical processes.
4. The use of a special “gasket” between the rails and the ground. This leads to a slight rise of the structure above ground level. As a rule, embankments made of a material that does not conduct electric current are used for these purposes. Such a solution increases the cost of the structure and cannot always be used for trams or subways located within the city.

Active

There are situations when passive protection methods do not work, are ineffective or cannot be implemented in specific conditions.

Active protection feature:

1. A small range, reaching only a few tens of meters.
2. The goal is to eliminate the anode areas, namely the places where currents exit the soil.
3. The principle of operation is the installation of cathodic protection, which “quenches” stray currents by supplying a “positive” potential to the protected structure. Cathodes are placed nearby, to which a “minus” is applied.

The cost of such a design is insignificant in comparison with the benefits that its use can bring. Over time, the installed protection wears out, so it needs to be replaced.

Elimination of anode zones is possible with correct calculations. If you make a mistake in the calculations, the effect can be reversed and the currents created will lead to even greater destruction.

As an additional method, an electrical drainage protection option can be used.

Wandering swamps in everyday life (in an apartment)

When considering the issue, the appearance of stray currents in residential buildings cannot be ruled out. They can appear in heated towel rails, water pipes, heating systems, gas water heaters and even boilers. Consider the main options.

Stray currents in a heated towel rail

With proper construction, the appearance of stray currents is excluded. This is due to the fact that all structures along the riser are metal and are grounded in the basement.

It turns out that the current potential is divided, and voltage may appear between the riser and the heated towel rail.

There are other reasons for the appearance of stray currents in such structures:

• close use of two types of steel: stainless steel and black;
• poor insulation of the wiring;
• network break;
• grounding for the heating system, etc.

1. Prepare a wire with a cross section of 2,5 square meters. mm.
2. Connect all the metal parts of the bathroom with a wire.
3. Make a jumper, namely, connect the conductor and the wire on the switchboard.
4. Secure the ground to the heated towel rail with a metal clamp.

Stray currents in the heating system

In any house or apartment there is a heating system and plumbing.

This leads to the appearance of incoming and outgoing stray currents that negatively affect the metal.

In addition, the causes of stray currents in pipes include:

• damage to the insulation in the washing machine;
• hidden / open wiring problems;
• violation of the integrity of heating elements;
• hit of fasteners in the wiring;
• location near power lines, etc.

1. Replace metal pipes with plastic ones (in the heating system).
2. If the first option is not suitable, use plastic inserts.
3. Perform grounding.
4. Install cathodic protection (can be installed in multi-storey buildings).
5. Check wiring to avoid leaks.

in the boiler

The water heater has increased risks for human health, because it is made of metal and is constantly in contact with water.

It is impossible to exclude the appearance of stray currents that occur in electrical equipment of high power.

The correct way is the following:

1. Make an outlet with a grounding contact. It should be installed at a height of more than 80 cm from the floor, and 50 cm from the heater.
2. Use a 3-core cable with one core insulated green/yellow. That is what needs to be grounded. The wire from the socket must be brought to the shield and connected to ground.
3. When laying the cable, make a strobe or use the external laying method.
4. Turn off the main switch and connect.

In a gas column

Another place for the occurrence of stray currents can be a gas column. The reason for this phenomenon may be the presence of a power line or electric transport nearby, as well as improper grounding.

Its installation is a prerequisite according to SP 402.1325800.2018. It may also be necessary to find the location of the incorrect grounding to correct the problem.

Results

Stray currents are not a myth or fiction of physicists, but a real problem that needs to be dealt with. If nothing is done, the likelihood of corrosion of metals in the potential area increases.

At risk are not only underground metal structures located in the area of ​​power lines, electrified railways, subways and trams, but also household items: a water heater, a heated towel rail, a plumbing / heating system, and even a gas water heater.

That’s why you need to know how to measure and protect against such a phenomenon.

References: 1 Privezentsev, V.A. Power cables and high-voltage cable lines / V.A. Privezentsev, THIS. Larina. – M.: RAGS, 1995. – 120 p. 2 Fridkin, I.A. Operation of cable lines 1–35 kV / I.A. Friedkin. – M.: Energy, 1972. – 88 p.