Are you familiar with the situation when the panel is small, but you want to fit a lot into it? For example, a box for 12 or 15 modules is already installed, and then a great idea comes to mind – to install both a two-pole main circuit breaker and a voltage relay and differential protection at the input. And you still need to protect all group lines (these are circuit breakers and differential protection devices), provide busbars for neutral and protective conductors...
How to fit all the necessary protection devices into the panel? The residual current circuit breaker (RCCB) AD12MS, which combines several protection functions, will help us with this.
What types of protection should be at the entrance to the panel?
In an apartment panel, the installation of circuit breakers and differential protection devices is mandatory. In the PUE (Electrical Installation Code), the installation of an RCD or RCCB is recommended in clause 7.1.71. In SP 256.1325800.2016, clause 10.13, it is stated that differential protection must be provided for all socket circuits. There are separate requirements for sockets installed in damp rooms.
By differential protection we mean devices that disconnect the power supply in the presence of a differential current. As a result, protection of a person from direct and indirect contact with wires and other objects under dangerous voltage is implemented.
In addition to differential protection in group circuits, which protects people, a "fire protection" device (RCD or RCCB with settings of 100 or 300 mA) must be installed at the apartment input. This will additionally protect against fires due to leakage current to grounded objects in case of insulation deterioration.
With such comprehensive protection, the risk of electric shock to a person, as well as the risk of fire, is minimized.
And what about other protection devices – SPDs, surge protective devices, voltage relays? Partially, additional protection can be provided by the AD12MS residual current circuit breaker.
AD12MS – 4 types of protection in one housing
Let's consider the functions of the AD12MS.
Overcurrent protection. This function is also called protection against overload and short circuit. We think for regular readers there is nothing new here: any RCCB has such protection.
Differential protection. AD12MS is produced only with two ratings of residual operating currents: 100 and 300 mA, it is perfectly suitable for installation at the input.
Selectivity. The letter "S" in the name AD12MS indicates its selectivity with respect to differential current. This means that the device will trip on differential current with a delay of not less than 0.1 s. Why is this needed? To ensure selectivity of two-stage differential protection schemes.
In the PUE, clause 7.1.73, and in SP 256.1325800.2016, clauses 10.13 and A.4.2, two parameters are mentioned: the tripping setting (rated residual operating current) and the tripping time. To fulfill the requirements of these clauses, the differential current rating at the input must be 3 times greater than in group devices. The same applies to the tripping time. Then, if a leakage occurs in one of the groups, the protection on that particular line will operate, and the others will continue to work.
Overvoltage protection. As a result of a broken working neutral or human error, a voltage of up to 380 V can be supplied to home appliances, which will damage the connected devices. Unfortunately, this happens not so rarely. Therefore, overvoltage protection is so important.
The letter "M" in the name AD12MS just speaks of this function: the power supply will be disconnected as soon as the input voltage exceeds the level of 265 V. Thus, the same function as in a voltage relay is implemented.
Please note: AD12MS does not fully perform all the functions of a voltage relay. After all, a voltage relay not only trips at the upper level, but also knows how to automatically turn back on when the voltage returns to normal.
However, in the PUE, clause 7.1.21, only disconnection is mentioned, and other functions are not mentioned.
Moreover, if the voltage has risen above 265 V, then we are talking about a serious accident that requires human intervention, and automatic switching on can even be harmful.
The AD12MS differential circuit breaker is a multifunctional device that is also very compact: its size is only three modules.
Conclusions
AD12MS is an excellent option for a device at the apartment input. However, before installing it, a few more facts should be taken into account:
- We recommend additionally installing RCDs or RCCBs with a rated residual operating current of 10 or 30 mA on socket circuits. This is necessary for guaranteed human protection.
- In life support, security, communication and fire extinguishing systems, it is better not to use automatic disconnection based on differential current and voltage deviation.
- In some cases, instead of AD12MS, you can use an AD12M type residual current circuit breaker (has only overvoltage protection) or AD12S (selective). Read about them in our article: https://dzen.ru/a/Xx7W_bZG3VRuGu8j