Heat is quite possibly the single most critical element affecting the life of components in a switchboard. The inside components, such as fuses, circuit breakers, contactors, and wiring, are all designed to operate within a specified temperature limit. When the temperature exceeds the maximum operating level, it can lead to a series of problems, including:

• Accelerated Degradation: High temperatures can also cause the materials in a switchboard to deteriorate at an increased rate. For example, plastic materials can melt or become bent, and metal materials become corroded.
• Decreased Life: The lifespan of electrical components in a switchboard depends directly on temperature. As temperature increases, the life of components is greatly decreased. It is an approximation rule that for each increase of 10°C above the maximum tolerable temperature, the life of the components decreases by half, and their rate of failure is doubled.
• Increased Failure Rate: Components that experience high temperatures will fail. High temperatures may destroy insulation, resulting in electrical shorts or fires.

Heat management is thus highly essential in maintaining the reliability of a switchboard and ensuring it remains safe to use for decades.

The Science Behind Heat in Switchboards

To know how heat influences switchboards, it’s important to learn how heat is transferred in switchboards. The heat transfer in a switchboard primarily happens through three methods:

• Thermal Conduction: Heat is transferred through materials such as the metal components within the switchboard.
• Convection: Heat is transferred from the internal parts to the air within the switchboard. This method is significant for cooling the switchboard.
• Radiation: Heat is emitted in the form of infrared radiation, but this is a lower consideration relative to conduction and convection.

Heat is generated inside the switchboard by electrical components as they carry out conduction and control of the flow of electricity. Since the generated heat cannot be expelled easily, the internal temperature rises, which creates a dangerous condition for equipment inserted inside.

Heat and the Maximum Operating Temperature

Each switchboard is built with an operating maximum temperature in mind, that is, the highest temperature at which the components can operate without degrading. When temperatures in a switchboard exceed this point, the internal components can be harmed by overheating, which can result in lowered performance, early failure, or even complete breakdowns.

The ambient temperature at which a switchboard is made to operate is determined by the material and component that it is made of. However, when the ambient temperature exceeds the maximum by some 10°C, the lifetime of the component is approximately halved. It is a critical concern as this equates to higher cost in the form of replacement, repair, and downtime.

Natural Cooling vs. Forced Cooling

When it comes to heat management within switchboards, there are two primary cooling processes: natural and forced cooling. Understanding these processes and where to use them is key to preventing breakdowns based on heat.

1. Natural Cooling

Natural cooling occurs when the internal heat of the switchboard dissipates into the surrounding environment without any active heat management system. This is accomplished through the walls of the switchboard, where heat dissipates naturally.

This method is most efficient when the temperature inside the switchboard is significantly different from the outside. For example, if the inner part of the switchboard is hotter than the surrounding air, then the heat will naturally shift from the interior components to the outer air. Natural cooling cannot always be relied upon, however.

For natural cooling to be used by a switchboard, the heat from internal components must be fairly low. When more than 500 watts of heat is being generated by a switchboard, natural cooling is not sufficient. In such cases, more active cooling systems are necessary to manage the temperature and maintain the components at safe working temperatures.

2. Forced Cooling

When natural cooling is insufficient, forced cooling comes into operation. Forced cooling makes use of fans and filters to drive air into the switchboard, spreading heat evenly and helping to evacuate it from the system. Fans are installed to blow air inside the switchboard, allowing space for the heat to move towards the walls, where it is let out into the external world.

For forced cooling to work, it’s important to determine how much air the fan needs to ventilate. The fan size and airflow capacity will depend on the heat load, the temperature difference between the interior and exterior, and the type of equipment inside the switchboard. Forced cooling, if required, must be attained by selecting fans with adequate capacity to absorb the heat and keep the internal temperature within safety limits.

Calculating the Heat Load in a Switchboard

To ascertain whether natural cooling will be adequate or whether forced cooling is required, the heat load in a switchboard must be calculated. Heat load is the total of heat generated by electrical equipment in the switchboard. This can be calculated in either of two methods:

• Using Power Dissipation: Each electrical component in the switchboard will have a datasheet that provides its power dissipation (amount of heat it produces). By adding up the heat generated by all components, you can determine the total heat load in the switchboard.
• Using Electrical Draw: Without power dissipation, the generated heat can be calculated by measuring the current draw of each device in the switchboard, multiplying it by the supply voltage, and correcting for the equipment efficiency. The sum of all devices’ outputs is used to give the total heat load.

Once the heat load is determined, it can be used to ascertain whether the switchboard requires natural cooling or forced cooling.

Prevention of Moisture and Cold in Switchboards

In addition to heat control, moisture can also be harmful to the internal components of the switchboard. Moisture can lead to corrosion and damage to the electrical components. This is especially in cold environments where condensation may take place inside the switchboard.

To prevent accumulation of moisture, heaters against condensation may be installed inside the switchboard. These heaters keep the inside of the switchboard slightly above the dew point, and hence moisture does not form on the parts. This is also useful in protecting the equipment and allowing the switchboard to function without any loss of efficiency even during low temperatures.

Temperature Control using Thermostats

For controlling the temperature in a switchboard, thermostats are utilized. Thermostats can detect the temperature electronically and turn the fans or heaters off or on as needed. Thermostats are needed to maintain the temperature level constant and enable the cooling system to function only when needed, which helps save energy and prevent overheating.