Understanding Insulation Voltage Markings: 300/300V, 300/500V, 450/750V, 600/1000V - U0/U Explained

Question

As I wrote above, in this way U0 / U are marked with insulation wires. I don't understand one thing about these markings. For example, take the 450 / 750V insulation marking, it says that the wire insulation is made for a single-phase voltage of 450V and a phase-to-phase voltage of 750V. If...

Anonymous · Accepted Answer

Because between one core and the ground there is one insulation, and between 2 wires is 2x thicker due to the fact that there are two insulations (each wire has its own).

Anonymous · Accepted Answer

Isolation is not 450V. At most, the rated voltage of this insulation can amount to this amount. Exactly. The external element is also a braid of a wire / cable or a cable armor, and a shield. Wire insulation, for example 450 / 750V, is given in the U0 / U format, where, as given in the link I sent: The phase voltage in the Polish power grid is 230V. As you know, the phases are shifted to each other, and between the individual phases the voltage is 400V. More precisely, it is 230 * root of 3. The same in the wire - 450V is the phase insulation voltage, and the wire (i.e. phase-to-phase) voltage is 450V * square root of 3, which is 750V. This cable is not suitable for operation in a two or three phase network. Why? Because between the phase conductors you can have a voltage of max 300V. Such cables are used, for example, to connect a lamp with two packages of bulbs.

golec2604 · Answer

There is something wrong with your translation. First of all, the neutral / zero wire also has insulation. Secondly, as you say, 2 x 450V for one wire gives 900V for two wires, not 750V. Can someone explain how is it ??

Anonymous · Answer

It was not about the neutral wire, but about the element outside the wire, e.g. a hand holding the wire. But it is not that simple ... As the manufacturer says that 750 is 750, not 900 because someone wanted to be wise and multiplied it.

golec2604 · Answer

1. Let's say that we have a 5-core cable and we have a three-phase voltage "so-called force", the insulation of each single wire (out of these 5 wires) between it and the external element is 450V, and between the two wires is 750V. I understand well ??

2. I am very curious how it is that a single conductor insulation is 450V and when we consider two conductors where theoretically the insulation should be doubled, but it is much less, i.e. 750V?

3. I am interested in 300 / 300V insulation, since single insulation can withstand 300V, why the increased insulation does not give increased strength, but 300V is further?

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I am asking for answers in points 1,2,3 and some human explanation.

Anonymous · Answer

Bad naming, but in a way yes. These voltages are the voltages that the insulation must withstand while meeting the appropriate conditions (depending on the measurement methodology). It is not a defect if it says 450/750, and the insulation is 2000, still within the standards. Take a look: Znakenia-kabli-norma-polska/

golec2604 · Answer

Could you please answer the individual questions separately? Second, expand your bad naming thinking I looked at this link, but there are only cable markings. I do not know what you mean.

elpapiotr · Answer

Really ?

Anonymous · Answer

No 780V, but for some reason they mean 750V. Unless I didn't understand the question.

golec2604 · Answer

Thanks to Kraniec_Internetów for a great explanation. I searched the Internet for such an answer for a long time before I asked the question here, but I did not find it.

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I do not really understand the answer to the 3rd question because if the maximum interfacial voltage is 300V, where can you find such voltage?

One more question has now arisen for me. Having a 5-core cable / wire, we can use it to release 3 phases, so the marking 450/750 is correct. But why use such a marking in a cable / 3-wire conductor where we can only release one phase, so the marking should be only 450V.

Anonymous · Answer

In some countries there are networks where the phase voltage is equal to the line voltage (60 degree phase shift), but that is not the point. The designation 300/300 tells us that the same phase can be applied to different phase cores of the same conductor. For example, we have a 300/300 4-core cable with brown, black, blue and yellow-green wires. We can install 2 lamps on this cable, connected by different phase conductors (black and brown), and activated with different switches. They must be powered from the same phase so that the voltage between these wires does not exceed 300V. When both lamps are on, the voltage between the wires is 0V (both 230V to the ground). When we turn on only one, it is 230V. There are also devices powered from 2 phases, such as welding machines and induction hobs. Such a cable cannot be used to power these devices.

golec2604 · Answer

I would like to ask you more.

.Jack · Answer

Rather, it was written before: So one value relates to the insulation resistance to voltage between any conductor and the external insulation The second value relates to the insulation resistance to voltage between the two inner insulations and not the outer insulation. During normal operation of the electrical system, the voltage in the 1-f system does not exceed 250V. But please take into account the possibility of switching overvoltages or short-circuit conditions. The rated insulation of cables is also selected taking into account the external conditions occurring in a given location, and often in special locations and installations where the 700 series standards recommend the installation of cables with reinforced insulation. And then there is no discussion here anymore.

czesiu · Answer

And how to understand the two voltages in the marking of single-core cables, e.g. YKY 1x120 0.6 / 1kV? 1kV applies to two cables lying next to each other?

golec2604 · Answer

I was thinking today and I still don't understand a certain thing. Having a multi-core cable / wire, e.g. with a rated insulation voltage of 450/750 V, informs us that the insulation of a single core was made for a phase voltage of 450 V. And the second value of the phase-to-phase voltage was calculated by multiplying 450 x sqrt (3) = 780 - manufacturers they take a value less than 750. Ok, almost clear about the markings. But there is one thing that I don't understand.
Since each single wire has an insulation that can withstand the phase voltage of 450V, if we wanted to determine the strength of the phase-to-phase voltage between two wires in this cable, every logical person would say that it is 900V (because it consists of two identical insulations withstanding 450V)

Calculating the inter-phase voltage based on the knowledge of the phase voltage and vice versa is not difficult because we will use the sqrt (3) converter. But here it is not about calculating the voltages, but about calculating the insulation resistance to the given voltage. So it is logical that by having two identical insulations and adding their values we will get a total.

I don't understand why the producers mean 450/750 and not 450/900 ??

Wirnick · Answer

Or maybe on the other hand - what is the rated value? 450 - can be used in a 230V 1F installation with a safety factor of about two times, and 750 - 3F - also about two times. The manufacturer offers the product for use in domestic installations with a guarantee of resistance to voltage breakdown of the insulation. I'm just thinking.

Anonymous · Answer

Well of course. After all, this is the minimum voltage that the insulation MUST bear. A breakdown can also occur at 1kV or at 10kV. Simply put, of course.

golec2604 · Answer

Please reply to what I asked.

Krzysztof Reszka · Answer

In the underlining, you have the answer why the producers write two voltages. Now read what is the RMS voltage.

Darom · Answer

I must admit that as always I understand Col. Reszka, now what is he talking about with this effective value? I guess I'm sleepy ...

Krzysztof Reszka · Answer

And what not to understand, an example.
The maximum value of the residential voltage equals; rms voltage / square root of 2, i.e. 325 V.
Manufacturers, writing 350 V on the cable, then meet the minimum requirements for a given cable, which was 325V.

Anonymous · Answer

However, according to the PN-88 E-02000 standard:
"In the international standard, it is recommended that the voltages at the point of energy supply during normal operation of the 50Hz alternating current network above 110 to 1000V should not differ by more than +/- 10%"

Krzysztof Reszka · Answer

The standard about supplied energy is for consumers and has nothing to do with the insulation parameters used by manufacturers.

Wirnick · Answer

The 450/750 (rated values) information does not have to be satisfactory for you - use 0.6 / 1kV - for exaggeration and swelling. In the final stage of production, multi-core cables usually undergo an insulation test with a voltage of 4kV (I am talking about their use in municipal installations). European regulations also apply to those conductors where the protective conductor is without insulation. Now another note - In any type of 3x400V network and installation, the phase voltage is not greater than 230V + -15% with respect to the protection voltage. So much for analysis for now.

golec2604 · Answer

No offense, but when you read your statements, you write nonsense, you probably do not know what it is about.
Mr. Krzysztof Reszka, I see that you are confusing. See the definitions:

Quote:

The marking on the cable 300 / 300V, 300 / 500V, 450 / 750V, 600 / 1000V indicates the rated voltage (effective value) of the cable insulation where (U0 / U)
U0 - RMS voltage between any conductor and the "earth" or cable shield
U - RMS voltage between any two phase conductors (phase-to-phase voltage)

You see in the definition it says "rated voltage (RMS)". If you don't know, I'll explain what they mean:
Rated voltage - Voltage rated value (nominal, normal, typical) - the value at which the device operates in accordance with the standards or manufacturer's recommendations. Exceeding this value causes incorrect operation of the device, changes in parameters or its damage.
RMS value - it is the rms value of a periodically changing signal, examples of such value are typical voltage in an apartment / house 230 V for one phase and 400 V phase-to-phase.
What you gave was the conversion of the effective (i.e. average) value into the maximum value. In the definition of insulation, he writes about the effective value (and not the maximum value) that the insulation must withstand.

So taking the example of a wire with an insulation strength of 450/750 V - it tells us that it will withstand a voltage of 450 V single-phase effective voltage (and not the maximum one) between the conductor and the earth or screen, and that it will withstand an effective inter-phase voltage of 750V between any two phase cores.

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My question is still valid. Let us take into account the case of a wire with insulation at 450/750 V. Since the insulation of one core will withstand 450 V of effective voltage, then when we take into account two identical wires, i.e. a double increase in insulation, then there is also no double value of the insulation strength, i.e. 900 V, and there is 750V ??
It is logical that 2 x 450 gives 900V, so where does the lower value come from, i.e. 750V ??

retrofood · Answer

Similar questions have already been asked on the forum many times. Each phase to N has 230 volts, and there is only 400 volts in between. Quackery! Producers of wires and cables cannot count, I do not even mention measuring. That's what!

Anonymous · Answer

Oh, it's hard to see math. The phase voltage is the line voltage * square root of 3. The maximum value is the rms value * square root of 2. Do you think square root of 2 = square root of 3?

Krzysztof Reszka · Answer

It is not logical, because it is the material used by the manufacturer that determines its use. Why does he write in the DTR to what voltage and what application it is intended for. And adding tensions to each other by keeping the veins together appears to be lacking in knowledge. An example of a cable that looks identical from the outside. Telefonica; Cables for industrial and agricultural workshop equipment, boilers, electric heaters, portable lamps, electric tools such as drills, circular saws, household electric tools, and also portable motors or machines on construction sites or on farms etc., also for permanent installation in temporary buildings and barracks for power. They are suitable for wiring components in lifting equipment, machines, etc. For use in dry, damp and wet rooms. Also for use at low temperatures in the open air for caravans, for heaters cars and camping. Use with voltages up to 1000V AC is allowed in fixed secured installations (in conduit or devices), as well as for motor connections cranes or the like H07BN4-F - cable made according to the harmonized standard (H), voltage 450 / 750V (07), on isolation from heat-resistant EPR rubber (B) and a heat-resistant EPR rubber coating (B ), with flexible veins (F) Cables intended for common use in households, kitchens, offices and households powering devices where the cables are exposed to small mechanical stress (e.g. kitchen appliances, flasks soldering irons, toasters) also for use at low temperatures. They are not suitable for continuous use on in the open air, in agricultural or industrial workshops and for powering portable tools except domestic H05BN4-F - cable made according to the harmonized standard (H), voltage 300 / 500V (05), on isolation from heat-resistant EPR rubber (B) and a coating of heat-resistant oil-resistant and flame retardant rubber (N4), with flexible conductors (F) We close the topic, it has been exhausted.

Understanding Insulation Voltage Markings: 300/300V, 300/500V, 450/750V, 600/1000V - U0/U Explained

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