Power
The rated power of the relay in kilovolt-amperes, in other words, the maximum apparent load power with which the device can normally operate.
From a physical point of view, kilovolt-amperes and kilowatts mean the same thing, but in kW it is customary to indicate only the active power of the load (see below), and in kVA — full. In AC networks, these powers can vary because active power (the power consumed by resistive-type devices such as heaters) is added to reactive power (the power consumed by capacitors and inductors). The apparent power is calculated from these two quantities.
When selecting control relays for AC networks, it is best to take into account the full power, especially if you plan to connect equipment with electric motors to the device. However, for many modern household appliances, only active power is given in the characteristics — in kilowatts. There are calculation methods that allow converting active power into total power, depending on the type and characteristics of the load; such techniques can be found in special sources.
Rated current
Rated switching current for which the control relay is set. In some models, this parameter can be changed at the request of the user; for such devices, the current value set in the factory settings is indicated (usually, this is the maximum indicator).
For a voltage relay (see “Device”), the rated current is the maximum current allowed for the device and the network segment protected by it for an unlimited time, in fact, the maximum current in normal operation. Exceeding this current is allowed, but not for long (up to several minutes) and not much, not higher than the maximum current (see below). And devices with the functions of a current relay or a power relay can work as follows: if the actual current is between the rated and maximum, the relay goes into the “delayed off” mode, and turns off the power after a certain period of time (for example, 10 minutes). This avoids both overload from long-term operation at high currents, and unnecessary power outages at large, but short-term permissible loads.
Maximum current
Maximum switching current allowed for the control relay. This is the maximum current that the device can safely pass through itself. And for models with current relay functions (see "Device"), this is also the default threshold of instantaneous operation — the current at which the relay instantly turns off the power to the load. In many models, you can set a lower threshold, but not a higher one.
Reclosing delay
The reclosing delay is the time after a safety shutdown after which the device turns on the mains power again. Usually, in modern control relays this time can be adjusted, so the characteristics indicate the range from the minimum to the maximum value.
Adjustment of the delay allows you to adjust the format of the relay to the characteristics of the network. So, if voltage failures do not mean critical problems, you can set the minimum re-closing time, and if jumps occur only with serious problems that need to be fixed, it is better to turn on the maximum delay. Note that triggered relays usually allow manual reclosing, and in most models it is possible to completely disable the automatic reclosing function.
Current trip limit
The upper current shutdown limit provided in the device is the threshold above which the relay switches off the protected network segment. Many models allow you to adjust this limit; for them, the range of such adjustment is indicated in the characteristics. Note that for the upper limit of this range, some manufacturers take not the maximum, but the rated current of the device; see above for details on these options.
