Isolation transformer in a home electrician workshop

Why can't ground the secondary winding? After all, then between the earth having some kind of potential close to zero and the potential on the secondary winding, when it is touched, a significant leakage current will be fatally dangerous to humans. It is necessary to make an independent ground loop in the protected room connected with the secondary winding, but separated from the power supply circuit of the transformer. This system, called "IT", is used, for example, in operating rooms, in addition, it is forbidden to install an RCD in the power supply circuit of the transformer and it is necessary to install a device that controls the insulation resistance of the transformer winding, not to mention the fact that home-made isolation transformers are prohibited in operation.

Isolation transformer (safety transformer) is a transformer whose primary winding is separated from the secondary windings by protective electrical separation of the circuits, that is, by double or reinforced insulation, or there is a grounded metal protective shield between the windings (paragraphs 1.7.44 and 1.7.49 PUE). Unlike a conventional transformer, the secondary winding of the isolation transformer is not grounded.

Isolation transformers are used where galvanic isolation of the primary and secondary (load) circuits is required, as well as isolation of the connected equipment from the ground loop. Without isolation, the limiting current flowing between the circuits is limited only by electrical resistances, which are usually relatively small. It is recommended to connect electrical equipment to the network, to increase electrical safety, increase reliability and service life, through an isolation transformer.

For example, according to the “Electrical Installation Rules”, bathrooms are included in the category of especially dangerous rooms due to the presence of increased humidity, flowing water and an abundance of metal products with unstable grounding. Installation of 220 V sockets is allowed only in a certain area of ​​such rooms, and special measures must be taken to protect against electric shock, in particular, the inclusion of sockets through an isolation transformer is allowed.

The use of such a connection of the power receiver significantly reduces the likelihood of electric shock, since the currents arising in the event of an insulation breakdown are of little importance, due to the galvanic isolation of the transformer secondary circuits from grounding circuits.

In transformerless power supplies with a small constant voltage at the load, with high probability it is possible to get under an alternating voltage of 220 V. In order for this to not happen and galvanic isolation is needed - the absence of electrical contact between the power and the load. I don’t know how relevant this is for power supply, transports are just too powerful, but an isolation transformer is an essential device for setting up electronic equipment!

I did not mean the grounding of the secondary winding of the transformer (error), but the bathroom equipment, since the rules provide for the mandatory performance of additional equalization of potentials, which is galvanically connected with the main equalization, that is, grounding, but according to paragraph 1.7.85 of the PUE and GOST R 50571.3:

- all cases of power receivers powered from one isolation transformer must be interconnected by a potential equalization conductor that does not have a ground connection (local non-grounded potential equalization system), PE conductors of other circuits and open conductive parts of other circuits;
- if the connection of electrical receivers is carried out using plug connectors, all plug sockets must have a protective contact connected to a local ungrounded potential equalization system;
- all flexible cables, with the exception of those supplying Class II equipment, must have a protective conductor used as a conductor of the local non-grounded potential equalization system;
- measures should be provided for from mechanical and other damage to the circuit conductors powered by the isolation transformer .---------- Although in my opinion this clause contradicts clause 1.7.104 of the same EMP, where grounding calculations are given for networks with isolated neutral, paragraph 2.4.4 of RTM-42 and European standards at the same time. To create an equal potential zone in the environment surrounding a person, it is necessary to provide also a FE-bus of the functional (working) grounding.

Thanks!

Thank you for the article! I have a question. Can an isolation transformer replace a voltage regulator? For example, for a gas boiler.

Can he cope with voltage drops? Or does he use it only for protective purposes?

Thanks!

Paul.

No, he can not. The isolation transformer has a different purpose. Read the article again.

Tell me, why, if the isolation transformer is so good, they are not placed in transformer booths at the entrances to houses, but they feed us with a dangerous phase with zero?

36 volts with such a switching circuit will be on one side of the screen with the network (when the network is connected at 5-15 and 5'-15 '), with a breakdown of insulation it can also kill ...

“when the TV was turned on, the lamp came on with a steady light - a short circuit in the power cord, in the input circuits of the power supply” - but should the fuse in the secondary circuit not burn out during a short circuit, and then the lamp will not light? Maybe the lamp should be in the secondary circuit?

Hello everybody. In a transformer booth, zero is still connected to the earth in the old fashioned way, out of habit. One hundred years ago, as some kind of smart person came up with this, they still do it here, they say that it’s for protection against electric shock.But in reality there is no protection !!! This is because the neutral wire connected to the ground is already connected to the person - the person is walking on the ground ... and it is worth touching the person by chance to another wire, called the "phase", it beats with current. Why does it strike at 220 volts? At high voltage, a high current passes through our body, and at low voltage, the current is weak. At 36 volts, a very small current passes through our body, a few milliamps. We may not even feel such a current. At a voltage of 220 volts, a current of much larger magnitude, several tens of milliamps, can already pass through our body. A current of 50 milliamps for a person is already dangerous, and 100 milliamps is deadly. Of course, there are different cases - if in a dry apartment a person stands on a dry floor, then he will not be shocked too much. But God forbid people to stand on damp earth and touch the wire "phase" - this is death.

I want to tell you why in those not very distant times, 100 years for history is nothing at all, they proposed and approved to connect the zero wire to the "ground". Electricity then only began to enter into the life of ordinary people. All this was very expensive, including wires from the power plant to the consumer. For an incandescent bulb, two wires must be brought in - zero and phase. So they decided to make one wire thinner, zero and connect it also to the ground. And then part of the current will pass through the earth, and part through the zero wire. Grounding was placed near almost every post and near the consumer's house. Everything turned out to be seemingly good. A thinner wire needed less metal. Non-ferrous metallurgy was then not very "advanced". Everything was very expensive. This is only later, when many modern power plants were set up and non-ferrous metals were smelted in electrolysis furnaces, metals became cheaper, including aluminum from which linear wires are made. Although the wires became cheaper, but still the neutral wire was still grounded and many thousands of people have already died from this grounded zero !!!! Abroad, they have long abandoned the grounded zero. There they conduct another third ground wire, really to protect human life. That's it.

Now I’ll also say why it’s advisable to have at least a 200–250 watt isolating transformer in the house, especially in the bathroom. Now we use many electric appliances in the bathroom as well: we blow dry our hair with a hairdryer, and we can put a small boiler into a glass. In the isolation transformer, it is no longer necessary to connect the zero of the secondary winding to the ground. The isolation transformer also serves to disconnect a zero from the earth. With such a connection of the wires of the secondary winding, we will not be shocked, even if we take on the phase wire of the secondary winding of the isolation transformer. This is because there will be no closed circuit between the zero of the separation transformer and the person. And do not listen to the current clever specialists, that it is necessary to ground zero in the bathroom. Only electrical enclosures need to be earthed !!! And in no case do you need to connect your zero to the body in electrical installations !!! Good luck to you all. Use electricity. It is very comfortable.

As a child, I watched how we did street wiring with us and it was very surprising to me that the electric wire was screwed to the exposed pipe of the gander riser. I knew then that it was impossible to touch electric wires, I knew how it nipped. Then, later I found out that this is a zero wire and it does not “beat”. And yet I still wonder how we relate to human life. It seems that everything is strictly safety precautions. At work, we sign for safety precautions that we are familiar with and strictly abide by the truth, and people die from electric shock. During my life, two people died at work with me.After the army, I worked at Selkhoztekhnika, where a tractor driver wanted to close the hood hatch in the winter and took hold of the electric lift box, and there he exposed three phases and killed him. Then I went to work in the city, there killed ELECTRICIAN. He was repairing an electric drive opening the gate there. If there were no grounded zero, people would not have died !!! And everything according to the rules, everything according to the instructions ... Why, then, do people die. So our instructions are not suitable !!! Urgent need to remove the grounded "ZERO"!

Incorrectly connected pins. This connection will not work, because the windings towards each other. The correct arrangement of the terminals of the primary 1-2 and 15'-5 ', and the secondary 2'-1' and 5-15

And I would not engage in amateur performances in the manufacture of such a vital device as an isolation transformer. Still, this is not the time of a general deficit. In any city there are specialized electrical shops where you can buy an industrially manufactured isolation transformer with guaranteed and proven electrical insulation properties. In addition, they are soaked, unlike television and are not afraid of high humidity. Life - it, brothers, is more expensive than any money!

Hello! Bought a transformer.

When connected to the network WITHOUT LOAD, it knocks out the machine. Why???

Opened.

Transformer "power" wire is three-wire. Zero, phase - clearly go to the primary winding (one of them through a fuse).

The ground wire is screwed to the metal casing and the ground contact of the load power socket.

- I measured the resistance of the windings - the same (I do not remember exactly, something about 3 Ohms), the difference in hundredths.

- “Rang” the power plug: “phase” - “ground”, “zero” - “ground. Do not“ ring ”.

- I did the same with the outlet for connecting the load. Everything is fine.

- He took out the fuse (i.e. disconnected one end of the winding) - the machine does not knock out. So the wire is normal, it won’t be somewhere "inside of itself".

Why can an automatic machine be knocked out idling? Shorty in the primary? But the resistance of the windings is the same and not 0.03 or 0.3 Ohm, which would be short.

By the way, the rubber legs on the bottom and the cover of the case are mounted ON THE TAPPERS, WHICH STOOR INSIDE and wires lie on them !!!

It is clear that the probability of cutting the sheath of wires through the sharp ends of the self-tapping screws is small, but as a fact of the "production culture" it is obvious. Screws "C grade" there would be more out of place.

And a socket for connecting the load - you look for such a plug. No, French teapots with a hole. And yet, I somehow never met other electrical appliances with such a plug.

Dmitriy,

The transformer is this: ... w.220-110.rf / product / ts220220-1500 /

Not an advertisement. It’s just that I’m not asking about “transformer in general” or some kind of homemade product.

Two electricians are sitting on a pole. Grandma is walking by. Electrician: granny .. let that wire lie on the ground .. Granny filed and went on. The first electrician to the second: I said "earth" ... and you - phase, phase ...

and why the light bulb in the primary circuit 220, and not in the secondary?
After all, the device under test will be connected to the secondary, it will take the short-circuit current from the secondary, we must protect the secondary, otherwise the secondary will be burned out by a faulty PSU. But in the pepper, insert the fuse and indicator lamp.

The essence of using an isolation transformer is to completely separate the receiver circuit from the power supply. This is an additional protection that does not relieve you of the obligation to exercise special caution and meaningfulness. Direct contact with devices powered by an isolation transformer (or IT network) is not 100% safe.It should also be remembered that after the isolation transformer, we do not distinguish between “L” and “N” - we have two “L”. Isolation transformers (with appropriate power) are the main element of the kits supplying power to the isolated “IT” power supply network. Some isolation transformers have a shield between the windings, which is supposed to replace the inner capacitance of the transformer with a smaller capacity on a straight surface, thereby reducing transformer leakage (through the longitudinal reactance). Such transformers are recommended for hospitals and as elements that provide protection against interference in recording studios, directors and laboratory measuring stands.