The priority relay is an electrical device of small size, the main task of which is to control the inclusion of electrical appliances. Briefly called it RPN. It is able to respond to an increase or decrease in load by switching off, and also controls the total current of the supply network. Using such a design allows you to get rid of the problem of excessive loads of electrical wiring.
Types of Relays
The priority relay is very popular in suburban and private houses, as well as multi-apartment buildings, industrial enterprises. The essence of the work is to divide the electric network into priority lines and less important ones.
There are several types of load priority relays:
- single and three phase;
- single and multichannel.
Three-phase structures are also capable of performing phase priority functions, distributing the load evenly over single-phase channels. This approach allows you to prevent a complete blackout of the entire object.
Multichannel load relays are used together with different types of lines.
By functionality, the equipment is divided into the following varieties:
- lower threshold;
- upper threshold.
The latter are triggered by an increase in current strength, are connected according to the series connection scheme. A device that operates at the minimum voltage threshold is connected in parallel.
Modifications are available that are designed for different levels of inclusion. It is possible to adjust the device for different loads. In networks with heavy loads, it is recommended to use them in conjunction with a current transformer.
Specifications and Design Features
The non-priority load disconnect relay is equipped with a built-in current meter, as well as an actuating element that switches contacts when the specified parameters are reached with a given time delay. The measuring element is able to monitor the current strength in a certain interval.
The maximum current switched by the built-in contacts, as a rule, is characterized by a standard value of 16 A. For switching high currents, contactors - magnetic starters are used. In such cases, the priority relay only provides a control pulse to it.
To control large currents, there are separate types of devices that allow you to connect external current transformers.
Application area
Inductive load relay is used when there is a need to configure the electrical network with limits on energy consumption. Similar situations occur when there are more users than this network can provide, and it is not possible to change its technical and design characteristics.
This miniature electrical device ensures uninterrupted operation and safe operation of a large number of electrical appliances, while maintaining the integrity of the network design. If you want to use, for example, a powerful device, non-priority ones need to be turned off manually or change the characteristics of the operated electrical circuit.
This approach is actively used in everyday life and in all industries.
Principle of operation and installation of on-load tap-changer
First of all, a current transformer is connected to the common line, and then after the consumers.In the first stage, loads are placed that have priority and should not be disconnected.
Next, a consumer relay is added to the circuit, with which non-priority load groups are switched. If the load in the power grid is exceeded, they will begin to gradually turn off in the sequence set by the person in order of importance.
A signal is sent from the current meter to the comparator built into the module. Its main task is to correlate the received signal with the settings set by a person. The relay determines the response time of the comparator, as well as the shutdown time of electrical appliances with low priority. This principle of operation helps to reduce the current strength in the network.
Model Overview
The high popularity of this type of equipment has led to the fact that more and more manufacturers are starting to produce it. Choosing a device that combines affordable cost and good quality is quite difficult.
The table shows the well-proven models.
| Manufacturer | Specifications | Approximate value in rubles |
| F&F (Poland) | The adjustable current range is from 5 to 90 A.
The interval for adjusting the low-priority circuit breaking current ranges from 2-15 A. |
2000 |
| Legrand 0 038 11 | The device is equipped with 5 modules.
The total current strength of connected consumers is 90 A. The trip threshold is 15, 20, 25, 30, 40, 50, 60 (A). |
1800 |
| Z – LAR / 8 | Frequency of switching no more than 3 600/60 minutes.
Rated voltage 250V. Turn-on current more than 3 A. Tripping current less than 1.8 A. |
1750 |
It is also recommended to pay attention to the products of ABB LSS, CDS Schneider Electric.
Disadvantages of using on-load tap-changer
Despite a rather extensive list of advantageous features, on-load tap-changers also have disadvantages:
- There is no way to install a priority relay on ordinary wiring, the circuit of which is not equipped with separate lines to outlets.
- To install the device in an existing network, it is necessary to perform many works that are related to the modernization of wiring.
To conduct separate wiring lines from the distribution panel, you will need to ditch the walls, so repairs throughout the room can not be avoided. This approach requires considerable financial costs, time and effort.
Common connection errors
There is a lot of supporting documentation that provides detailed on-load tap-changer connections, but people still make common mistakes. To warn them, you need to familiarize yourself with the following information:
- Inexperienced specialists or people without experience supply a phase to the contacts of the priority relay. In fact, they are intended for switching indicator lamps.
- Direct connection of loads to the on-load tap-changer, not via contactors. The maximum load of the device is not more than 16 A. The reason may be inattention or insufficient knowledge, neglect of the recommendations of the equipment manufacturer.
Another common mistake is the incorrect grouping of loads from consumers according to their importance. If solving this issue is difficult, it is better to seek the advice of professionals who will help you find priority equipment at home or in the workplace.
Priority Relay Analogs
To install a priority relay in an existing electrical network, you will need to do a lot of work, for example, to modernize the distribution panel and the wiring itself. Doing it yourself is not always possible, since you will need to accurately calculate the entire load scheme.
The solution to the problem became much simpler after the development of a new, more advanced device, which was called the network load optimizer.The principle of operation of the analogue is to redistribute the power of electrical appliances according to their priority. Design features are simple, the device is designed for easy operation. It is not installed in the panel, it consists of two adapters for the socket of the socket and the plug.
