The choice of protective automation for the electrical network is not just a formality, but a matter of safety of life and property. When installed in the shield introductory machine rated at 32 Amps, the owner is faced with a logical question: what differential protection (RCD) parameter will be optimal in this case? Errors at this stage can lead to either permanent nuisance tripping or, much worse, to a lack of current leakage protection.
The rated current of the differential current device itself must match or exceed the capacity of the machine. If the automation turns off the network during an overload of 35-40 Amps, then the RCD must withstand these currents without overheating the contacts. In this article we will analyze the technical nuances that will help avoid fire hazards and ensure stable operation of electrical appliances.
It is important to understand that a circuit breaker and an RCD perform different functions. The first protects wiring from short circuits and overcurrent, and the second protects people from electric shock and prevents fire due to leaks. Harmonization of their characteristics is the key principle of constructing a competent power supply scheme.
The principle of coordinating the ratings of the machine and the RCD
The basic selection rule states: the rated current of the RCD must be equal to or greater than the rating of the circuit breaker that protects it. For a 32A machine, this means that it is strictly forbidden to install the device at 25A - its internal contacts will burn out long before the thermal protection of the machine is triggered during a prolonged overload.
The standard range of RCD ratings includes values of 25, 40, 63, 80 and 100 Amperes. For a 32A input machine, the most logical and safe choice would be RCD 40 Ampere. This provides the necessary margin of safety. Some electricians recommend taking a reserve of two stages (for example, 63A) to guarantee the life of the device, but for domestic conditions 40A is quite enough.
โ ๏ธ Attention: Installing an RCD with a rating lower than that of a circuit breaker (for example, 25A on a 32A circuit breaker) is a serious mistake. At a current of 30-32A, the machine may not turn off for hours, and the contacts of the RCD will begin to heat up, which will lead to melting of the housing and a fire.
There is also the concept of "rated conditional short-circuit current". For the household series this is usually 4500 or 6000 Amps. Since the 32A input circuit breaker is located at the beginning of the line, it limits the short-circuit current, but the RCD must still have a margin for this parameter so as not to be physically destroyed at the time of the accident.
The main rule: The rated current of the RCD (In) must be >= the rated value of the machine. For 32A, the ideal option is 40A or 63A.
Selection of differential leakage current (Iฮn)
The second most important parameter is the sensitivity of the device, that is, the leakage current at which shutdown occurs. For input circuit breakers that protect an entire apartment or house, a dilemma often arises: to set 30 mA or 100 mA? This is where the concept of selectivity and total natural leakage comes into play.
If the 32A RCD is at the input and protects all electrical wiring entirely, then setting the sensitivity to 30 mA may lead to frequent false alarms. The total natural background of leaks from all operating appliances (refrigerator, boiler, computers) can approach the threshold of 30 mA. In this case, it is more reasonable to use a selective RCD (type S) with a leakage current of 100 mA or 300 mA.
- ๐ 30 mA - standard for the protection of socket groups, bathrooms and individual powerful consumers, where direct human contact with live parts is possible.
- ๐ 100-300 mA - used for input devices (fire protection) or in old houses with dilapidated wiring, where there is a high risk of fire due to leakage, but setting 30 mA is impossible due to false alarms.
- โก 10 mA - used only for particularly dangerous premises (for example, a bathhouse) or individual devices (water heater), but never installed on the 32A input circuit breaker.
The optimal scheme for a private house with a 32A input circuit breaker looks like this: at the input there is a 40A/100mA RCD (type S), and after it, groups with circuit breakers and a 30mA RCD are distributed. This ensures selectivity: in the event of a breakdown in the socket, the group RCD will trip, while the input one will remain on.
RCD types: A, AC or F?
An equally important aspect that is often ignored is the type of response to the current shape. Standard devices type AC respond only to sinusoidal alternating current. However, modern household appliances (washing machines with inverters, LED lamps, computers) consume current with a pulsating DC component.
For such consumers it is necessary to use an RCD of the type A. They are capable of capturing both sinusoidal and pulsating leakage currents. Installing a cheap type of speaker in a modern house with a 32A input circuit breaker may be useless, since the device simply โwill not seeโ a dangerous leak from a new washing machine.
What is the difference between type A and AC?
RCD type AC is cheaper, but only reacts to alternating sinusoidal current. If the circuit contains a device with a rectifier (diode bridge), the leakage may be pulsating. The type of speaker may not react to such a leak or may operate with a delay. Type A is universal and mandatory for modern technology.
There is also a type F (Frequency), which is designed to protect equipment with frequency converters, but it is rarely found in everyday life. For a standard circuit with a 32A machine in a residential apartment or house, type A is the gold standard for quality and safety.
Connection diagram and switching order
Correct assembly of the shield requires consistency. The input cable (phase and neutral) first comes to the 32A circuit breaker, and then from it is fed to the RCD. This scheme allows you to protect the differential protection device itself from short circuit currents.
If you connect an RCD in front of the machine, then in the event of a short circuit on the line, the short circuit current will pass through the contacts of the RCD. Although the machine will turn off, there is a risk that the arc discharge inside the RCD will weld its contacts and it will fail. Therefore, the rule โMachine -> RCDโ is a priority for the introductory group.
Diagram: Network input -> Automatic 32A -> RCD (40A/30mA or 100mA) -> ConsumersDuring installation, it is important to connect the neutral correctly. The neutral wire after the RCD cannot be combined with zeros of other groups or grounding, otherwise the device will be knocked out instantly. To check the correct assembly, there is a "Test" button on the device body.
โ๏ธ Checking the shield assembly
Table of correspondence between ratings and characteristics
For ease of selection, we present a summary table that will help you quickly determine the necessary equipment parameters in conjunction with a 32 Ampere input circuit breaker.
| Parameter | Minimum value | Recommended value | Note |
|---|---|---|---|
| RCD current | 32 A | 40 A or 63 A | Current reserve is required |
| Leakage Current (Input) | 30 mA | 100 mA (type S) | For selectivity of the entire network |
| Leakage Current (Groups) | 10 mA | 30 mA | For outlets and wet areas |
| Reaction type | AC | A | For modern technology |
The table shows that the minimum permissible current of the RCD coincides with the current of the machine, but this is a limit value. Engineering practice dictates the use of the next rating in the series (40A) to eliminate operation at the limit. This is especially true at high temperatures in the shield in summer.
Common installation mistakes
One of the most common mistakes is ignoring the thermal regime. A 32A circuit breaker can continuously pass a current of 32A at an ambient temperature of +30ยฐC. If the panel is densely packed and the temperature is higher, the actual tripping current may shift. An RCD fitted end to end will degrade under such conditions.
Also a common combination of zeros. After the RCD, the neutral wire should go only to the protected group of consumers. If you โthrowโ the zero to another branch or accidentally touch the ground, the protection will work. This is not a malfunction, but a correct operating algorithm.
โ ๏ธ Attention: Do not use comb busbars to connect RCDs from different manufacturers without checking compatibility. The contact pitch may differ by 0.5 mm, which will lead to poor contact, heating and fire. For 32A it is better to use separate wire jumpers.
Another mistake is installing an RCD in TN-C grounding systems (where there is no separate ground wire, only PEN). In such old houses, it is possible and necessary to install an RCD (to protect against leakage through a person), but it will only perform the function of protection upon contact, and not upon breakdown to the housing (since the housing is not grounded). In this case, the choice of quality type A is especially important.
Frequently asked questions about choosing protection
Is it possible to install a 25A RCD if the circuit breaker is 32A, but the load is small?
No, you can't. The rating of the RCD is selected not according to the actual load, but according to the rating of the machine that stands in front of it. A 32A circuit breaker can pass current up to 32A (and even higher at certain temperatures) for a long time. A 25A RCD is not designed for such a current; its contacts will overheat, which will lead to damage to the device or a fire.
Why does the 32A/30mA RCD trip when the washing machine is turned on?
Most likely, the total leakage current in your network is approaching 30 mA. The washing machine has a natural leak to the interference filter. If there is already background from other devices in the network, adding a machine exceeds the threshold. Solution: check the wiring insulation, separate the lines, or (if this is an input RCD) increase the setting to 100 mA, transferring the 30 mA protection to the socket group.
Is it necessary to install an RCD at 32A if there is a difavtomat?
A difavtomat is a combined automatic machine and an RCD in one housing. It makes no sense to install a separate RCD before or after the automatic circuit breaker on the same line, unless you implement a complex selective circuit. Typically, the 32A/30mA difavtomat completely replaces the โAutomatic + RCDโ combination.
How often do you need to check the performance of the RCD?
Manufacturers and PUE standards recommend checking the performance by pressing the "Test" button at least once a month. This simulates current leakage and tests the mechanical part of the trip unit. If the RCD does not turn off when the button is pressed, it must be replaced.