When you select a unit "machine" you are sure to stumble upon the parameter "breaking capacity". He indicated in kA (kA) It means the amount of current, he will stand at the short-circuit has arisen, while maintaining its efficiency. I.e., It works on off, and will not burn.
You can find in one and the same brand of the same denomination with different breaking capacity. On sale household model with the values of this parameter 4,5kA, 6kA and 10kA (everything, that more – already for industrial use). The higher this index, the higher the price "modulki".
for example, Eaton (to purchase an American corporation known as Moeller) It offers three series: PL4 with breaking capacity 4,5kA, PL6 and PL7 (on 6kA and 10kA respectively).
To illustrate the difference between guns, We use the online store "AksiomPlyus". so, tags at the time of preparation of the material (February 2018 year in terms of the currency):
PL4-C16 / 1 – 2,9 dollars,
Fla6-Cl6 / 1 – 3,61 dollars,
PL7-C16 / 1 – 6,25 dollars.
The difference between the cost of the first two already noticeable, about 20%, and at 10kA model will cost at all in 2 times more, than 4,5kA.
What caused the difference? And whether you need when searching for modular protection devices to pay more, chasing the highest breaking capacity?
In some cases, choose 4,5kA, 6kA and 10kA
In the bulk using gradation values 4,5kA, 6kA and, rarely, 10kA. These figures specified by the manufacturer in a rectangle on the front panel of the case.
What they mean: for example, in panel mounted circuit breaker 4,5kA. If there at the site short circuit to circuit 4,5kA it effectively work, break the emergency electric circuit, and it does not fail. When, when the fault current exceeds the rated value, guaranteed by the manufacturer, probably, that the machine oplavitsya or burn, failing to carry out their task.
Therefore, when choosing the nominal value, determine the probability of occurrence of emergency values, exceeding 4,5kA or 6kA.
according to the EMP (see. 3.1; 1.7; 7.1; section 6), in networks up to 1000V to safely disconnect the machine must meet the short-circuit overcurrent. If you do not go into short-circuit calculations, you can take as an example of the generalized conditions for installation in apartment buildings:
of 4,5kA – exhaust flaps in apartment;
of 6kA – opening flaps in apartment;
of 10kA – extending in the input switching centers (on input power line in the house).
Why is that – Let us be clear. Дело в том, that the magnitude of the current (including short-circuit) in a conductor is inversely proportional to the resistance (all remember Ohm's law from the school physics course?) – i.e., it is the lower, higher resistance.
В свою очередь, wiring resistance is directly dependent on several factors, including the proximity of the substation (the closer, the higher the value of short-circuit currents can occur), wiring material, quality connections.
To prevent accidents in the homes of old housing, in rural areas and country houses, where battered wiring made of aluminum cable, you'll find most marked 4,5kA. this is enough.
In apartment buildings, wherein the wiring is made good using copper wires (copper cable has less resistance, than aluminum), the absolute values of short circuit potentially increase. Here, it is desirable to provide a dielectric strength 6kA. by the way, demand for 6kA "machines" predictably grows.
What is the most expensive to 10kA? It is considered an exceptional relevance for the protection of industrial plants. However, the currents of such values may well be formed in the immediate vicinity of an electrical substation. Therefore, to protect the power lines cottages, town houses and other buildings on the 2-3 этажа, especially those located in the vicinity of the transformer substation, choice of induction machines to 10kA – rational decision.
Under whose brand to buy
Interesting, that depending on the parameter range of the breaking capacity of low-voltage equipment from well-known brands is quite different.
Допустим, You decided to limit 4,5kA. Будьте готовы к тому, that in the afternoon with fire you will not find such models in some of the leading manufacturers of low-voltage equipment – eg, ABB, General Electric, Hager.
Дело в том, that is not used modulka with breaking capacity lower than 6kA in Europe, not to comply with their higher safety standards.
Other brands produced a series on 4,5kA specially for the CIS market. for example, advertised line "Brownie" from Schneider Electric. Not a problem to find such and IEK.
Как правило, This device structure cheapening. So, in Legrand and Schneider Electric does not provide output for connecting comb tires. A window display of contacts able to perform only at Eaton and inexpensive IEK (кстати, to honor the manufacturer's).
Many stores Electrical apparatus on 4,5kA up the bulk of the range, wherein the high demand (including for the most affordable prices).
Sales occasionally come across "fossil" on 3kA (eg, by Asko-Ukrem). In addition to the cost of the cheapest on the market, any advantage they do not have. We do not recommend the use of.
Difficulties may arise when looking unipolar "machine" to 10kA. So, ABB in such a modular does not exist, therefore have to choose from the same Eaton (Moeller), Hager, IEK and a couple of lesser-known producers such as the Slovak SEZ.
But the denomination 6kA represented in all brands, are "on ear". These are the "domestic" demand in Europe Machines.
Which ultimately choose for themselves
When you select can not be guided solely by considerations of economy and current recommendations.
The new apartments and private homes with powerful energy consumers, high-quality copper wiring (section of the cable 4 мм2. for "odnushki" and by 6 мм2. for a more spacious housing) appropriate to use circuit breakers with breaking capacity 6kA.
Modular panel of filling in the cottage, town house or other building on 2-3 floor provides a margin of safety in the "commissioning". Especially on the subject, Located close to the transformer substation. If the budget allows, take a higher level of protection, the 10kA.