Switchgear assembly is critical to the reliability of the electrical installation. It must comply with clearly defined standards governing the design and construction of low voltage devices.
Switchboard assembly is the creation of a point at which the input power source is disconnected into separate circuits, each of which is controlled and protected by fuses. This design is divided into several functional blocks, each of which contains all the electrical and mechanical elements that contribute to the performance of the claimed function. For example, the assembly of a 380v switchboard in a private house is necessary in order to create a key link in the reliability chain.
Therefore, the type of construction should be ideally adapted to its application. Its design and construction are required to comply with applicable standards and working methods.
The enclosure assembly of the switchboard provides triple protection:
- First of all, it is the safety of measuring devices, relays, fuses, etc.
- The distribution panel assembly must include protection against mechanical influences, vibrations and other external factors that may affect operational integrity (electromagnetic interference, dust, moisture, parasites, etc.).
- Protection of human life from the possibility of direct and indirect electric shock.
Switchboard Types
The load requirements determine the device models that will be installed.
Switchgear assemblies 380v and below may differ depending on the type of application and the accepted design principle (especially regarding the location of the tires).
The main types are:
- The main low voltage model is MLVS.
- Engine Control Centers - MCC.
- Sub-distribution switchboards.
- The final model.
And the last three-phase switchboard assembly is designed for specific applications (e.g. heating, elevators, industrial processes). It can be located:
- Near the main low voltage facility.
- Near the attached items.
- Subdistributive and final switchboards. usually spread throughout the area.
Two technologists
Distinguish:
- Universal switchboards in which all kinds of devices, fuses, etc. are attached to the chassis at the rear of the chassis.
- Functional models for specific applications based on a modular and standardized design.
Universal
The switchgear, as already noted above, is usually located on the chassis in the rear of the housing. That is why the assembly of the switchboard with your own hands is very simplified. But it should be borne in mind that the display and control devices (meters, lamps, buttons, etc.) are installed on the front panel.
The placement of components inside the case requires a very careful study, taking into account the size of each element, the joints that must be made with it, and the gaps necessary to ensure safe and trouble-free operation.
Functional Distribution Boards
As a rule, these are models designed for specific applications. They consist of functional modules, which include separation devices, together with standard accessories for mounting and assembling a switchboard, and connecting, which provides a high level of reliability and a large capacity for changes at any moment in the future.
Many advantages
The use of functional assemblies of distribution electric switchboards has spread to all levels of low-voltage devices, from main to final, due to their many advantages:
- The modularity of the system, which allows you to integrate all kinds of functions in one model, including protection, maintenance, operation and modernization.
- Self-assembly of the switchboard and its design is quick. Because this model, unlike others, simply includes the addition of functional modules.
- Of course, assembling a private house distribution board can be even faster. This is due to the fact that for the average user, developers are trying to simplify the design as much as possible.
- Finally, these models are subjected to type tests that provide a high degree of reliability. Do-it-yourself assembly of the switchboard has become not only faster, but also safer.
Schneider Electric's Prisma G and P range of functional devices requires up to 3200 A and offers:
- Flexibility and ease of construction.
- Certified to IEC 61439 and guaranteed service in a safe environment.
- Saving the time of assembly of the switchboard with your own hands in stages, from design to installation, operation and modifications or updates.
- Simple adaptation, for example, to meet specific work habits and standards in different countries.
Fixed
Basic switchboards use three main technologies. Fixed - these units cannot be isolated from the power source, so any intervention for maintenance, modifications, etc. requires disconnecting the entire device. However, plug-in or plug-in models can be used to minimize shutdown times and increase the availability of the rest of the installation.
Disconnectable
Each function block is mounted on a removable board and is equipped with isolation means on the input side (busbars) and disconnection at the output (circuit). Thus, the entire device can be removed for maintenance without a general shutdown.
Retractable
The assembly of the metering switchboard and related accessories in this case is a little complicated. This is because the devices, for completeness of functions, are mounted on a retractable horizontal chassis. This model is usually complex and often involves engine control.
Isolation is possible on both the input and output sides by completely removing the drawer, which allows you to quickly replace a failed unit without disconnecting the rest of the switchboard.
Standards
Compliance with applicable standards is essential to ensure an adequate degree of reliability.
The IEC 61439 series of standards (Low Voltage Switchgears and Control Devices) has been developed to provide end users with a high level of trust in terms of safety and availability of electricity.
Reliability aspects include:
- Harmless to people (risk of electric shock).
- Fire protection.
- Explosion hazard.
Accessibility of power supply is a major problem in many sectors of activity, which can lead to significant economic consequences in the event of a long interruption due to a failure of the distribution board.
The standards establish design and verification requirements, so failure should not be expected in the event of a malfunction, violation or operation in harsh environmental conditions.
Compliance with standards should ensure accurate operation of the switchboard not only in normal conditions, but also in difficult ones.
The three elements of the IEC 61439-1 and 61439-2 standards contribute significantly to reliability:
- Clear definition of functional units.
- Separation forms between adjacent blocks according to user requirements.
- Clearly defined screening tests and routine screening.
Standard structure
The IEC 61439 series of standards consists of one basic postulate (IEC 61439-1), containing general rules, and several related theses detailing which of them are applied (or are not used, or should be adapted) for specific types, for example, distribution assembly shield in the apartment:
- IEC / TR 61439-0: Definition Guide.
- IEC 61439-1: General rules.
- IEC 61439-2: Power switchgears and controls for assembly.
- IEC 61439-3: Shields intended for use by ordinary people.
- IEC 61439-4: Particular requirements for devices for building sites.
- IEC 61439-5: Assembly of electrical distribution panels in public networks.
- IEC 61439-6: Busbars.
- IEC / TS 61439-7: Assemblies for special applications such as marinas, campsites, market squares, electric vehicle charging stations.
The first edition of these documents was published in 2009, and revised in 2011.
End-user expectations requirements
Various applications included in the standards have been introduced in order to meet numerous expectations:
- The ability to operate electrical installations.
- The ability to withstand high voltage.
- Current carrying capability.
- Withstands short circuit.
- Electromagnetic compatibility.
- Protection against electric shock.
- Service and modification options.
- Probability of installation in place.
- Protection against fire risk and environmental conditions.
Clear definition of responsibilities
Switchboards are qualified as assembly ones, including switching devices, control, measuring, protective, regulating equipment, with all internal electrical and mechanical connections and structural elements. Assembly systems include machine and electrical components (housings, tires, function blocks, etc.).
The original manufacturer is the organization that has carried out the entire design and associated assembly verification in accordance with the standard. He is responsible for the design tests listed in IEC 61439-2, including many electrical samples.
The inspection may be controlled by a certification body licensing the original manufacturer. These documents can be transferred to the specifier or to the end user upon request.
The manufacturer of the assembly, as a rule, is an organization that takes responsibility for the completed construction. The model should be completed in accordance with the instructions. If the manufacturer of the assembly is based on the guidance of the original inventor, he must conduct a structural inspection again.
If there are deviations, they must be submitted to the original creator for verification. At the end of the assembly, routine tests should be carried out by the distributor.
The result is a fully tested model for which the original manufacturer performed design checks and the final manufacturer performed routine inspections.
This procedure provides better end-user reliability compared to the Partially Validated approach proposed by the previous IEC60439 series.
Design requirements
In order for the assembly system or switchboard to comply with the standards, different requests apply. These requirements are of two types:
The assembly system design must comply with these requirements under the responsibility of the original manufacturer.
Switchboard installation
This is one of the most important work, which should be carried out only according to the instructions provided. This document must be attached with the goods at the time of purchase. If there is a good and understandable scheme, such installation turns into a purely technical task and does not represent any difficulty. Moreover, at the very beginning it is necessary to ensure the correctness of all connections of individual user groups and the reliability of connections. To begin with, it is worth unpacking everything and preparing the necessary additional tools.
The assembly of the shield itself is carried out only after wiring is installed in the room or office in accordance with the instructions provided. The ends of the products of each group are marked, inserted from below into a pre-mounted shield and bifurcated or torn apart, depending on the need.
Power input is from above. DIN rails are formed in the shield. Then zero and grounding tires and a sorting box for the phase cable are installed. Installation of safety devices is carried out from top to bottom and from left to right with their synchronous connection according to the diagram. Zero cores are introduced into the N tire, and those operating safety earth are introduced into PE.
During the installation of the shield, it is necessary to observe the color ratios of the products to its multifunctional purpose: white - phase, blue - zero, yellow-green - safety ground. This kind of procedure will make it possible to exclude many errors.
Depending on the features of the internal tie and the installed circuit, the sorting board may contain a common protection device, RCD, switches, zero and main grounding cover, flowmeter and other equipment.
Without exception, all innovative devices have a specific width that is a multiple of one value - the module (18 millimeters). Thus, a unipolar apparatus is 18 mm, that is, one segment, two-pole 36 millimeters — two, etc. A single-phase RCD has a width of 2 modules, three-phase - 4. Such a design makes it possible to choose a steel shield according to the number of segments and type contacted devices.
Integrated sorting devices are formed in a niche and then coated with cement. The depth of the collection must also be set according to the scale of the shield, taking into account the wall thickness.
Grounding and zero tires require brass plates with holes and screws for reliable wiring. They can be installed in a special heat-insulating block with the prospect of mounting in a DIN rail.
When installed in apartment rooms, modular panels make it possible to preserve the aesthetics of interior decoration. In order to install devices in the rear wall of the sorting element, specialized iron contour profiles are formed - DIN rails.
The overall dimensions of safety devices from different manufacturers can vary both in width and in elevation. Therefore, when receiving these devices, it is necessary to concentrate attention not only on industrial properties, but also on their straightforward scales. This will make it possible to effectively use safety panels in order to provide an aesthetic outdoor type.
After installation of the equipment and execution of the electrical connections in the switchboard, an iron or plastic panel is installed on top of it, hiding the device terminals, cable and DIN rail and protecting it from touching live parts. Slots are made in the panel, ensuring the visibility of devices and access to their controls. The vacant part of the slot is covered with plastic plugs.
When assembling the sorting board, all wires that must be marked without fail are first introduced into it. This eliminates the majority of assembly errors. For marking purposes, as a rule, use masking tape with numbers or multi-colored electrical tape.
For the device of branching of phase wires, sorting constructions can be used, which make it possible to connect conductors of different cuts and guarantee protection against touching the current-carrying part due to a replaceable tire. The case of such a unit is made of a fire-resistant substance that is stable to heat and has excellent electrical insulation properties.
When communicating wires, special attention must be focused on the correct connection of the RCD. The most popular error is considered to be connecting it to a group, in the circuit of which there is a union of a zero working conductor with open conductive parts of the electrical installation.
Short sequence
The installation of the sorting board contains the following procedures:
- installation of a metal box of the required volumes;
- marking on the supply wires with the prescription of the category number and section, and connecting them with the corresponding devices;
- the introduction of pre-marked devices in the stand and cutting their ends;
- setting the priority for the placement of safety parts in accordance with the distribution scheme of consumers into groups;
- fixing of DIN-rails and serial connection in accordance with the scheme;
- marking each device with the prescription of the category number for which it is specialized in order to avoid probable errors;
- accuracy control of all connections according to the marking of input wires and protective devices of all groups.
Already after the installation is completed, the beams of the same name must be tightened with special screeds and put in free areas of the shield.
The readiness of the RCD to operate can be tested using the control key, which is supplied with each safety shutdown device. When it is pressed, an electric current leakage into the earth is formed, which should activate the inclusion of the working device.