Comparison Zubr MF2-63 red vs DigiTOP VP-3F10A

The number of phases for which the relay is designed.

— 1. Single-phase power is known to everyone from classic 230 V household sockets. Actually, some relays for this voltage are even made in the form of socket adapters (see "Installation"). However, models are also produced for other values of alternating voltages — for example, 110 V.

— 3. Three-phase 400 V power supply is used mainly for high consumption devices for which 230 V networks do not provide enough power. Also note that switchboards in private houses are often connected to a three-phase electrical network, with further power distribution for individual phases. However, in such cases, it is more reasonable to use three separate relays for each of the phases, and not one three-phase device: in the first case, only part of the home network will lose power in the event of a power failure, in the second, the entire network.

— 1/3. A specific variant used exclusively in the phase selection relay. Such models take three phases as input, and only one is fed to the load; see "Device" for details.

Width expressed in unit units. This unit is used to measure the width of rack-mounted devices and makes it easy to estimate how much space you need. Width in unit is always expressed as whole numbers, 1 unit is approximately equal to 17.5 mm. There are models 1U, 2U, 3U and more

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 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 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.

Voltage measurement range supported by the device.

Many modern control relays are equipped with digital displays, which can display, including current voltage; this parameter specifies the operating range of the built-in voltmeter. In this case, the voltage measurement range can be noticeably wider than the difference between the smallest minimum and the largest maximum shutdown threshold (see below). This allows you to use the relay also for online diagnostics of the network status.

For a current relay (see "Device") in this case, the range of operating voltages can be given directly — the voltage at which the device can normally perform its functions.

Measurement accuracy provided by the device. In this case, different types of measurements may be implied, depending on the purpose of the relay (see "Device"). Note that in power relays and multifunctional devices, the measurement accuracy for voltage and current is usually the same, and a common parameter is given in the characteristics for them.

Accuracy is indicated by the maximum measurement error provided by the device. First of all, the operation accuracy depends on this parameter: the lower the error, the smaller the actual deviations from the specified operation parameters. For modern control relays, an indicator of 3 – 5% is considered acceptable, 1.5 – 3% is not bad, 1 – 1.5% is good, less than 1% is excellent. However, in fact, it is also worth choosing according to this parameter, taking into account how sensitive the connected load is to the accuracy of the specified operation parameters.

Also note that many modern relays are equipped with digital displays that can display various parameters. In such models, the measurement accuracy also determines the accuracy of the readings of such a built-in "tester".

Time to turn off the device on the lower limit of voltage or current. This is a kind of "reaction time" of the relay: the period of time between reaching the lower limit and turning off the protected network segment.

The lower this value, the more advanced the protection will be, the lower the probability of failure of sensitive devices due to untimely operation of the relay. On the other hand, a high response rate for the lower limit is not as critical as for the upper one, and the shutdown time can be quite long — 1 s or more.

Also note that for some devices, this paragraph gives the minimum turn-off time (fastest response time), while in certain modes this time may be longer. For example, a voltage relay with a lower limit of 160 V may provide tripping after less than 0.05 s when the voltage drops below 120 V and tripping after 1 s when the voltage is in the range of 120 – 160 V, but above 120 V. This avoids unnecessary shutdowns with relatively weak and short-term voltage deviations. In the characteristics of such a device, 0.05 s will be indicated.

The device shutdown time on the upper limit of voltage or current. This is a kind of "reaction time" of the relay: the period of time between reaching the upper limit and turning off the protected network segment.

The lower this value, the more advanced the protection will be, the lower the probability of failure of sensitive devices due to untimely operation of the relay. Note that a short reaction time in this case is especially important, because too high a voltage or current is a serious danger to any device.