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How to create an electrical switchboard diagram?

Before assembling an electrical panel, you need to identify all the existing consumers and calculate the total power consumption.

Each diagram consists of a set of elements. By knowing their designations and functional features, you can easily read the existing panel layout or create a new one. Let's review the main elements.

The main elements of the electrical switchboard diagram

1. Input circuit breaker or switch

For efficient disconnection of electrical power at the input, it is recommended to use a main switch or circuit breaker. If the electrical panel serves as the point of entry and contains the primary electrical meter, it is better to install a circuit breaker at the input. This will provide additional protection to the electrical system against overloading and short-circuit currents. However, if the panel is installed downstream from the one containing the primary meter and is equipped with a circuit breaker, then a main switch is sufficient for this panel.


The rating of the input circuit breaker is determined based on the cable cross-section and the power consumption. For instance, for apartments with electric stoves and cables with a cross-section of 10 sq. mm, a circuit breaker with a rating of not more than 50 A (11.5 kW) can be installed; for apartments with gas stoves and electric ovens and cables with a cross-section of 6 sq. mm, a circuit breaker with a rating of not more than 32 A (7.5 kW) can be used, and for cables with a cross-section of 4 sq. mm, a circuit breaker with a rating of not more than 25 A (approximately 6 kW) is suitable.

2. Selective SSD 

In houses or apartments with a large number of consumers and dedicated lines, you need to install a selective residual current device. This is an additional protection in case of current leakage. Its distinctive feature is the ability to set the trip time and overcurrent trip parameters. For correct operation of the system, both of these parameters must be set three times higher than for other SSD
in the system.


If several panels are connected in series, it is enough to install one selective SSD in the metering panel.

3. Voltage monitoring relay

The Voltage Relay (VR) allows you to set a range of acceptable voltage fluctuations, and in case the readings exceed the specified limits, it disconnects all consumers from the power supply. Once the voltage returns to the normal range, the relay automatically reconnects the power supply. This helps protect the equipment from excessive voltage fluctuations.

There are single-phase and three-phase voltage relays. Three-phase relays are used for consumers that require consistent voltage across all three phases and adherence to their sequence. In cases of distributed phase loading, it is recommended to install protection on each of the phase lines.

DS Electronics manufactures ZUBR voltage relays of various capacities. These devices are characterized by high precision voltage measurements due to the True RMS algorithm. The relays' enclosures are made of special non-combustible plastic, and they are equipped with a thermal protective relay to prevent overheating and potential fire hazards.

If your house receives three-phase power, you can protect your electrical equipment using one of the methods mentioned above. The primary criterion for choosing a specific method is the presence of three-phase loading (e.g., a three-phase electric motor). If such a load is present, you should consider only method 1 or 3.

Method 1: ZUBR 3F three-Phase Relay in combination with a Contactor (contactors are not included in the kit).


Advantages:

  • protection of three-phase loads.
  • compact installation in the distribution panel (compared to three separate three-module single-phase relays).
  • potentially a more cost-effective solution.

Disadvantages:

  • in case of a fault on any of the phases, the relay will disconnect the load on all three phases (in other words, the entire building will be de-energized until the fault voltage is restored).

Method 2: three single-phase ZUBR relays (double-module (D2, D2 red), or triple-module (D, Dt)).


Advantages:

  • in case of a fault on any of the phases, the relay will only disconnect the load connected to the faulty line. The rest of the equipment will continue to operate normally.
  • the ability to set a longer delay for the phase with equipment that has a compressor. The other phases can be reconnected faster after the fault.

Disadvantages:

  • not suitable for protecting three-phase loads (e.g., three-phase motors).
  • possibly less cost-effective solution.

Method 3: combination of the first and second methods. To achieve this, it is necessary to split the three-phase line at the input into two separate lines. One of them will be used to protect the three-phase equipment using a three-phase relay, and the other will be used to protect other single-phase equipment using three single-phase relays.


Advantages:

  • universal and individual approach to protecting three-phase and single-phase equipment.
  • the ability to set a longer delay for the phase with equipment that has a compressor. The other phases can be reconnected faster after the fault.
  • in case of a fault on any of the phases, the relay will only disconnect the load connected to the faulty line and the three-phase load. The rest of the equipment will continue to operate normally.

Disadvantages:

  • the most complex and costly among the three methods.
  • requires more space in the electrical panel.

4. Ammeters and Voltmeters 

The presence of these devices allows visual monitoring of voltage or current levels. This is important when there is a need for real-time redistribution of the load among phases in case of power deficiency on one of the phases.

5. Group Lines

Next, according to the scheme, there is a division into lines for groups of consumers equipped with automatic circuit breakers (CB) and SSD (safety shutdown device).

It is recommended to allocate separate lines for powerful consumers such as electric ovens, boilers, washing machines, and underfloor heating. Additionally, specific areas such as garages, workshops, saunas, and bathrooms should have their own dedicated lines. Rooms with high humidity and appliances in contact with water, like dishwashers, washing machines, and boilers, must be equipped with RCDs with a nominal differential tripping current of up to 10 mA.

Each designated line should be protected by an SSD and CB. It is possible to install one SSD for multiple lines, provided that its nominal capacity is higher than the total capacity of all CB. Alternatively, combined CB-SSD devices (dual-rated circuit breakers) can be used.

6. Connectors and Distribution Busbars, Wires, etc.

When creating an assembly diagram for an electrical panel, it is necessary to specify the methods of connecting devices together and the method of connection. For this purpose, the presence of various busbars, terminal blocks, wires, etc., is separately marked and indicated on the diagram.

Tips for constructing an electrical switchboard diagram

An electrical panel diagram is essential for providing a visual representation of the device arrangement and the sequence of their connections. It aids in the assembly, repair, and modernization of the electrical panel. Here are several tips to consider while creating the diagram:

  • prioritize safety on three levels – protection of individuals, wiring, and electrical devices – by installing appropriate protective devices.
  • label all devices and connections on the diagram – this will facilitate the assembly process and help identify faults in the future.
  • use standard symbols or provide a separate legend for the diagram.
  • create distinct lines for high-power consumers and separate areas.
  • follow the principles of time and current selectivity for additional protection.
  • plan for future upgrades and increased consumer capacity by incorporating reserves into the design.

Programs for creating an electrical switchboard diagram

To simplify the process of creating a panel diagram, there are numerous programs available. Both regular graphic editors and specialized software for electricians can be used for this purpose.

One of the simplest and most functional programs for creating a panel diagram is «1-2-3 Scheme.» It includes a vast library of various devices that can be selected based on their ratings. Additionally, the program allows printing labels with designations for placement on the panel. More detailed information about different software for electricians can be found in our previous article.

Creating a diagram is a crucial and responsible stage in assembling an electrical panel. The accuracy and thoroughness of the calculations at this stage determine not only the stability of the entire electrical system but also its potential for future expansion and modernization.