What Is an Electrical Panel? Construction, Working Principle and Functions

What is an electrical panel?

An electrical panel is a box-shaped enclosure made of steel or stainless steel, used to house, protect and connect electrical components into one coherent operating system. Inside it you may find circuit breakers (MCCB/MCB), contactors, thermal overload relays, inverters (VFDs), soft starters, PLC controllers, HMI screens, copper busbars and a range of other supporting components.

The most common English term is electrical cabinet or control panel. In Vietnamese, depending on context, it is also called a control cabinet, an industrial electrical cabinet, an electrical board or a distribution board.

An electrical panel performs three main functions in any electrical system. First, equipment protection against dust, moisture, impact and external electromagnetic interference. Second, power distribution from the main supply down to each load in a controlled, safe manner. Third, operational control covering starting, stopping, speed adjustment and real-time status monitoring of equipment.

Industrial electrical panel construction

An industrial electrical panel has two main parts: the enclosure and the components inside it.

• Cabinet shell is the outermost protective layer, and it determines how well the panel copes with its environment. Powder-coated galvanised steel suits dry indoor conditions. Stainless steel 304 or 316 is mandatory in damp or chemical environments and in food-industry cleanrooms. In deep-freeze stores, the enclosure also needs insulation or an internal heater to prevent condensation forming on the electronics when the temperature outside the panel drops below 0°C (32°F).
• Inside the panel components are arranged by functional zone. The busbar zone receives power from the main supply and distributes it to the branches. The switching zone holds the MCCBs and ACBs protecting each separate circuit. The control zone houses the PLC, interposing relays, timers and terminal blocks. The display zone carries the indicator lights, meters and HMI.

The key components in an industrial electrical panel are: the main circuit breaker (ACB), branch breakers (MCCB/MCB), motor starting contactors, thermal overload relays, inverters for speed control, soft starters to limit starting current, the PLC/SCADA controller, terminal blocks, phase indicator lights and energy metering devices.

Common panel types

Electrical panels are classified by several criteria: function, operating voltage and field of application. By function, the 6 most common types are the main switchboard (MSB), the distribution board (DB), the PLC control panel, the SCADA control panel, the motor control centre (MCC) and the automatic transfer switch (ATS).

Main switchboard (MSB)

The MSB (Main Switch Board) is the entry point for the entire electrical system, installed immediately downstream of the step-down transformer. It takes power from the national grid, usually at 0.4 kV (400V), and distributes it to the DBs and the larger loads. An MSB in an industrial plant can have a rated current of up to 6,300A and be fitted with an ACB capable of breaking short-circuit currents up to 85 kA.

Distribution board (DB)

The DB (Distribution Board) takes power from the MSB and distributes it to individual equipment groups or production areas. A DB typically uses MCCBs as branch switching devices, together with protective fuses and phase indicator lights. A large plant may have anywhere from 5 to 20 distribution boards depending on its size.

PLC control panel

A PLC (Programmable Logic Controller) panel is an intelligent panel that uses a programmable controller to automate production processes according to complex logic. Inside a PLC panel you will find the CPU that processes signals, I/O modules that gather sensor data, an HMI screen for the operator to monitor and intervene, and a 24VDC power supply for the control circuits.

In industrial refrigeration, the PLC panel sequences compressor starting, manages the evaporator fans, coordinates the condenser water pumps and monitors the temperature of each zone of the store. Tân Long PLC panels are running at many seafood plants, including the system driving 8 high-speed IQF lines at Kyokuyo Vina Foods Co., Ltd.

SCADA control panel

A SCADA (Supervisory Control And Data Acquisition) panel sits a level above the PLC, allowing the whole system to be monitored and operated from a central control room over an industrial network. SCADA gathers data from hundreds of measurement points, logs operating history, raises fault alarms and automatically optimises operating parameters.

The standout feature of a SCADA panel is remote connectivity over the internet or a local network, letting engineers monitor and adjust the system even when they are not on site. That is essential for large cold stores of 5,000 tonnes and above.

Motor control centre (MCC)

The MCC (Motor Control Centre) centralises the control and protection of every motor in the plant — pumps, fans, compressors and conveyors. Each compartment in an MCC manages one motor and supports several starting methods: direct-on-line (DOL), star-delta, soft start or inverter. Choosing the right starting method reduces starting current by a factor of 3 to 7 against DOL, extends motor life and saves a significant amount of energy.

Automatic transfer switch (ATS)

An ATS (Automatic Transfer Switch) panel automatically transfers the supply from the grid to a standby generator when the mains fails, with a transfer time of 0.1 to 10 seconds depending on configuration. Once the grid is stable again, it transfers back automatically. For a cold store holding thousands of tonnes of frozen food, an ATS panel is indispensable insurance against product loss during an outage.

Panel technical standards: IEC 61439 and IP rating

Control cabinet An industrial panel must satisfy two core groups of technical standards: construction and assembly requirements under IEC 61439, and environmental protection expressed as an IP rating.

The IEC 61439 standard

IEC 61439 is the international standard setting out design and testing requirements for low-voltage assemblies. It replaced IEC 60439 in 2012 and is widely applied in Vietnam at the request of foreign owners and on FDI projects. IEC 61439 specifies key parameters including rated voltage up to 1,000V AC, rated current, permissible short-circuit current, maximum temperature rise inside the enclosure and insulation capability.

A panel built to IEC 61439 must undergo two kinds of testing: design verification carried out by the manufacturer, and routine verification on every panel leaving the factory. Food processing plants exporting to the EU and Japan usually require this standard as a mandatory condition.

IP (Ingress Protection) rating

The IP rating expresses how well an enclosure keeps dust and water out, under IEC 60529. The IP designation has two digits: the first (0-6) indicates protection against dust, the second (0-9) protection against water.

In industrial refrigeration and food processing, the minimum IP rating for each application is as follows: a panel in a dry control room needs IP54 (dust-tight and protected against splashing water from any direction); a panel in a processing area washed down with a high-pressure hose needs IP65 or IP66 (fully dust-tight, resistant to powerful water jets); a panel outdoors or in a freezing room needs IP66 or better.

From projects at seafood export plants in the Mekong Delta, Tân Long has seen the same issue recur: panels originally rated only IP54 installed in workshops with a wet cleaning regime. After 12 to 18 months, internal condensation damages the relays and PLC. Upgrading to IP65 together with an anti-condensation heater resolves the problem for good.

Electrical panels in industrial refrigeration systems

Industrial refrigeration systems place demands on an electrical panel that ordinary applications do not. Continuous 24/7 operation, a wide temperature span, high humidity and flammable gases such as NH3 (ammonia) in natural-refrigerant systems all create their own engineering challenges.

• Control refrigeration compressor is the most important application. The MCC or PLC panel sequences the starting of the screw compressors in a predetermined order to avoid an electrical overload from simultaneous starts. For the NH3 system at Frescol Tuna Vietnam's 12,000-tonne cold store in Nghe An, Tân Long designed an MCC panel controlling 2 screw compressors of 250 kW each, with inverters unloading them to match actual demand.
• Temperature monitoring and alarms are a vital function in a cold store. The SCADA panel gathers data from hundreds of temperature sensors distributed throughout the store, displays a real-time heat map and sends alerts by SMS or email when temperature drifts outside the permitted band. In a freezer store held at -18°C (-0.4°F), a deviation of more than 3°C (5.4°F) for over 30 minutes can affect product quality and export compliance.
• Automated defrosting condenser is an application that receives little attention but directly affects system efficiency. The PLC panel schedules defrost cycles at the optimum interval for each evaporator, avoiding simultaneous defrosting across all coils, which would cause a sudden temperature rise in the store. The intelligent defrost schedules Tân Long programs save customers 8 to 12% of their power consumption compared with a fixed time-based setting.
• Integration with IQF lines is a specialised application on seafood freezing lines. The central control panel synchronises conveyor speed with actual cooling capacity, ensuring the product reaches a core temperature of -18°C (-0.4°F) before it leaves the IQF tunnel, while regulating NH3 or HFC flow to match the real heat load.

Tân Long control panels: solutions for food plants and cold stores

Tân Long has designed and manufactured PLC and SCADA control panels for the refrigeration and food industries since 2005. Our panels integrate hardware from leading brands such as Siemens, Schneider Electric and ABB, programmed by engineers with hands-on experience from dozens of cold storage facilities and processing plants.

What sets a Tân Long panel apart from an ordinary one is the control software: algorithms refined over many years of real plant operation, not template code running for the first time. Tân Long PLC panels support sequential compressor starting, load-following inverter control, intelligent defrost management and SCADA connectivity for remote monitoring.

Enclosures are manufactured at Tân Long's plant in Duc Hoa I Industrial Park, Tay Ninh (formerly Long An), to IP55 through IP66 depending on the requirements of each project. Stainless steel 304 panels are for wet processing areas and cleanrooms. Powder-coated galvanised steel panels are for control rooms and dry areas.

For detailed specifications and the full feature set of our PLC control cabinet and SCADA control cabinet, see the dedicated product page. If you need advice on a specific project, Tân Long's engineering team is ready to analyse your requirements and propose a suitable solution, from design through installation and handover.

In ammonia-based industrial refrigeration systems, the panel must meet additional specific safety requirements — see control panels for NH3 systems.

Frequently asked questions about electrical panels

How does an electrical panel differ from an electrical board?

An electrical board typically contains only basic switching devices such as circuit breakers and fuses, and is used in residential settings or small buildings. An industrial electrical panel has a more complex structure, with integrated control, protection and monitoring, built to withstand harsh conditions and run continuously.

What is the difference between a PLC panel and a SCADA panel?

A PLC panel controls equipment automatically on site according to pre-programmed logic. A SCADA panel collects data from several PLCs, visualises the whole system on screen and allows remote supervision. In most large plants, PLC and SCADA work side by side: the PLC handles real-time control, SCADA handles supervision and data analysis.

What IP rating does a cold store panel need?

A panel in a dry control room needs at least IP54. A panel in a wet processing area regularly washed down with a hose needs IP65 or IP66. A panel outdoors or in a freezing room needs IP66 together with an anti-condensation heater.

How long does an electrical panel last?

A good-quality steel enclosure lasts 15 to 25 years. Internal components such as relays, contactors and inverters usually need replacing after 8 to 12 years depending on duty. PLCs and electronics last 10 to 20 years provided the operating environment meets requirements for temperature, humidity and freedom from heavy vibration.

When does an electrical panel need upgrading?

A panel needs upgrading when the following signs appear: relays operating incorrectly on a regular basis, a PLC no longer supported by the manufacturer's software, total current approaching 80% of rated capacity, or the plant expanding with more equipment than the spare I/O on the existing PLC can handle.