How to select the RCD

By Admin | Electrical Light
10 May 2016
overload and short-circuit, preventing a fire due to leakage currents flowing on the ground.

RCD detect leakage of electricity from the appearance of the difference between the input and output currents, and when it occurs immediately de-energized loads.Thus, the leakage current flowing through the damaged insulation or through the human body, do not have time to cause damage.

Of all the electrical safety devices RCD is the only one that protects people from electric shock in direct touch to one of the live parts.

RCD is one of the most popular devices used as building corporations and private users.But in order to ensure the correct RCD buyer should take into account as working device operating parameters and characteristics that determine their quality and reliability.

RCD operating parameters: the rated voltage, rated current, rated residual current (leakage current setpoint).These parameters are selected based on the technical parameters of the designed installation.

quality and reliability o
f the RCD is determined by several parameters, primarily rated conditional short-circuit current (Inc) and nominal and breaking (switching) capacity (Im).Rated conditional short-circuit - a characteristic which determines the reliability and durability, quality of its machinery and electrical connections (minimum allowable value Inc = 3 kA.).Switching capacity according to the requirements of the RCD must be at least ten times the rated current of 500 A or

quality devices are usually much higher switching capacity - 1000, 1500 A. This means that such devices more reliable and accidentmodes, such as ground fault, circuit breakers, circuit breakers ahead, guaranteed to produce a trip.

For the best protection against out-of-control power it is advisable to install separate RCD or differential switches on each branch of the current consumption of the load with different characters.

For example, to prevent a fire in the kitchen, where there are many high-power electrical appliances require less sensitive switches.But they will not disconnect the electricity from each "throw" of the current caused by a refrigerator.And to protect the dedicated line to the bathroom you need to put the most sensitive devices "feel" even in leakage current of 10 mA.

For better electrical continuity and at the same time the maximum power is most preferable to install a separate RCD front of each circuit breaker.

It is this combination and represent a residual current circuit breakers (RCD + "machine" in one case).It should be noted that they are more expensive than single "machine" and the RCD, but more compact and significantly simplify the installation work.Such devices are better to put in the place of your circuit, where after the RCD is supposed to only one machine, such as a separate line in the washing machine.It is desirable that the RCD and the machines have a single firm, asOtherwise the RCD could work before the machine, thus taking the brunt, and quite possibly fail.

Selecting protective devices depends on the parameters of the network (1 or 3 phases and the rated current).However, the main component in the selection - is the value of the leakage current.The total leakage current of the network based on the merging of fixed and portable power consumers during normal operation should not exceed 1/3 of the nominal current of the RCD.In the absence of leakage current for power consumers should be at the rate of 0.4 mA to 1A load current and the leakage current of the network - at the rate of 10 mA per 1 m length of the phase conductor.

Approximate leakage currents arising from the use of household and office electrical equipment, are as follows: Fax 0.5 - 1 mA;Printer & lt; 1mA;Computer 1 - 2 mA;
appliance, depending on the availability of a constant component of the leakage current RCD may be of two classes: the "AS" and "A".The most common class is considered "AS", providing protection against leakage current of sinusoidal form variable.Prices RCD class "A" is somewhat higher, but the device of this class and provides protection from constant pulsating components in the leakage current.Some modern appliance manufacturers require the use of protective devices for units with "electronic stuffing."Appropriate guidance is available in the data sheet.

By their construction, electromechanical and electronic RCDs.The first does not require any power.For their operation enough to appear differential current.Secondly there is an electronic circuit and its operation need energy received or from the monitored network or from an external source.

Electromechanical RCD reliable, and they continue to perform the protective function even if one of the conductors.

Before buying a residual current device, you should pay attention to the labeling of the device - on the front panel of each RCD must be present value of the rated current that it can be carried out in continuous mode and the rated residual current device triggers.Other information may be arranged and on the side surfaces.