Beatrice Lang
Derating is a term used in electrical engineering to describe the process of reducing the maximum capacity or output power of a device or component to protect it from damage and prolong its life. This is often done in response to high ambient temperatures or other environmental conditions, such as installation altitude or mounting orientation, that can increase the temperature of the device or component and therefore impact its performance. Derating can also be necessary when installing multiple current-carrying conductors in a single raceway, cable, or covered ditch, as this can have a detrimental effect on the insulation of the conductors. By reducing the voltage, current, or power, derating helps to reduce the heat generated by the system or component, creating a buffer zone between the manufacturer's recommended maximum rating and the actual applied stress.
What does derating mean in electrical terms?
| Characteristics | Values |
|---|---|
| Definition | Reduction of output power to protect electronic components and devices from high temperatures and prevent failures |
| Application | Nearly all industrial power supplies |
| Temperature limit | Above 60 °C, the output power must be reduced linearly |
| Installation altitude | Derating is necessary above 2,000 meters |
| Mounting orientation | Derating is necessary if it deviates from the recommended standard installation |
| Purpose | To prolong the life of a device, increase average strength, decrease average stress, and decrease stress variations |
| Operation | Below the maximum power rating, current rating, or voltage rating |
| Safety | Provides a safety margin for transient voltages or currents (spikes) that exceed normal operation |
| Heat | Reduction of heat generated |
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What You'll Learn
- Derating is necessary when installing power supplies at altitudes above 2,000 meters
- Derating is required when mounting power supplies in non-standard orientations
- Derating is the reduction of the maximum capacity a unit can handle
- Derating is the operation of a device at less than its maximum capability to prolong its life
- Derating is necessary when installing more than three current-carrying conductors together
Derating is necessary when installing power supplies at altitudes above 2,000 meters
Derating refers to the reduction of the maximum output power of a device to protect it from damage and prolong its life. It is a protective measure to safeguard electronic components and devices from high temperatures and prevent failures.
When installing power supplies at altitudes above 2,000 meters, derating is necessary because the atmospheric pressure decreases, which leads to reduced air density. This lower air density diminishes the cooling effect of the convection airflow, resulting in higher temperatures that can damage the power supply. Therefore, to prevent system downtime and damage, the output power must be reduced above 2,000 meters, either by a certain percentage per 1,000 meters or by lowering the ambient temperature.
The required power derating values can be found in the data sheets provided by manufacturers, which include derating curves that indicate how to adjust the output current based on both temperature and altitude. These values vary depending on the specific power supply unit.
It is important to note that power supplies do not automatically adjust their output power in response to altitude or temperature changes. Instead, users must adapt the device to the ambient conditions during installation. This proactive adjustment ensures the power supply functions optimally and avoids potential issues caused by excessive heat.
Additionally, derating may also be necessary when the mounting orientation deviates from the recommended standard installation. This is due to the functionality of convection-cooled power supplies, where airflow enters at the lower ventilation grille, rises as it heats up, and exits through the top of the device. Deviations from this standard “chimney effect” can impact cooling efficiency and necessitate derating or ambient temperature adjustments.
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Derating is required when mounting power supplies in non-standard orientations
Derating is a protective measure that allows the use of power supplies at high temperatures, high altitudes, or in alternative mounting orientations. It is the reduction of the output power depending on the ambient conditions. Derating is, therefore, a recommended protective measure for electronic components and devices to protect them from high temperatures and prevent failures.
When mounting power supplies in non-standard orientations, derating is required to prevent these components from overheating, maintaining the power supply's longevity and reliability. The mounting orientation of a power supply can affect its airflow. If the airflow is impacted, the power supply may not cool the interior components as efficiently, leading to overheating.
The recommended standard installation position for power supplies is based on a "chimney effect". Cool air enters the power supply at the lower ventilation grille, heats up due to the power losses of certain components, and is discharged at the top of the device. This design ensures that temperature-sensitive components are placed in the coolest areas of the power supply.
If the power supply is mounted in a non-standard orientation, such as upside down or on a tabletop, the airflow can be disrupted. This can cause the components to overheat, reducing their lifetime and potentially leading to a failure of the power supply. To prevent this, derating or limiting the ambient temperature is necessary.
By reducing the output power and adapting the device to the ambient conditions, you can avoid system downtimes and damage to the power supply. This is especially important when mounting power supplies in non-standard orientations, as it ensures the components operate within a safe temperature range and prolongs their lifespan.
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Derating is the reduction of the maximum capacity a unit can handle
Derating is necessary when the ambient temperature is higher than the recommended standard installation, as the power supply will need to be convection-cooled. This is particularly important when the power supply is mounted in an orientation that deviates from the recommended standard installation, as the airflow inside the device cools the temperature-sensitive components.
Derating is also required at an installation altitude above 2,000 metres, as the reduced air density decreases the cooling effect of the convection airflow. In these cases, the output power must be reduced or the ambient temperature lowered.
Derating can also be necessary when there are too many current-carrying conductors installed together in a raceway, cable, or buried in the earth. This has the same destructive effect on a conductor's insulation as installing conductors in an elevated ambient temperature.
By reducing the maximum capacity of a unit, derating increases the average strength and decreases the average stress and stress variations, thereby extending the component's life and enhancing its reliability.
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Derating is the operation of a device at less than its maximum capability to prolong its life
Derating is a procedure used to protect electronic components and devices from damage caused by high temperatures. It involves operating a device at less than its maximum capability to prolong its life.
In electrical terms, derating means reducing the output power of a device to prevent it from overheating. All wires have some resistance, and this resistance generates heat. When multiple wires are placed in close proximity, such as in a conduit, the heat can build up quickly and lead to high temperatures. Derating helps to mitigate this issue by reducing the maximum capacity (load) a unit can handle.
For example, a wire designed to work at room temperature (70°C) will have a reduced ampacity when placed in an environment with a higher temperature, such as 100°C. The wire will still function, but the amount of amps that can flow through it will be lower. This reduction in capacity is a form of derating.
Derating is also necessary when power supply units are installed at altitudes above 2,000 meters. At higher altitudes, the atmospheric pressure and air density decrease, reducing the cooling effect of convection airflow. As a result, the output power of the power supply unit must be reduced to prevent overheating.
The derating curve for a device indicates how much it can dissipate without sustaining damage at different temperatures. This information is typically provided in the device's datasheet and must be considered when designing a system to ensure the long-term reliability of its components.
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Derating is necessary when installing more than three current-carrying conductors together
Derating is a necessary procedure in electrical systems to ensure safety and prevent potential hazards like electrical fires or equipment damage. It involves reducing the maximum capacity or output power of a device or conductor to protect it from high temperatures and prevent failures. This is particularly important when installing more than three current-carrying conductors together in a single raceway, cable, or covered ditch, as this setup can lead to heat accumulation and increased resistance.
When multiple current-carrying conductors are bundled together, the heat generated by each conductor can build up due to limited air circulation and the close proximity of the conductors. This heat accumulation increases the resistance of the conductor material, potentially leading to overheating and subsequent failure. By derating the conductors, the maximum allowed current (ampacity) is reduced, preventing the conductors from exceeding their safe operating limits.
The Texas SFM Electrical Code 2023 and the National Electrical Code (NEC) in the United States provide guidelines for derating conductors based on the number of conductors and environmental conditions. For example, according to Table 310.15(C)(1), a THWN No.4 copper conductor with a normal value of 85 amps must be derated to 80% of its value when there are 4-6 current-carrying conductors bundled together. The ampacity continues to decrease as the number of conductors increases, with 7-9 conductors requiring a derating to 70% of the normal value.
It is important for electricians to consider the impact of installing too many current-carrying conductors together and apply the necessary derating adjustments. This proactive measure helps maintain the integrity of the electrical system and prevents premature failure of the conductors' insulation due to excessive heat. By following the relevant electrical codes and derating factors, electricians can ensure the safe and efficient operation of the electrical system.
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Frequently asked questions
Derating in electrical terms means reducing the output power or running a system or component at a lower voltage or current to protect it from high temperatures and prevent failures.
Derating is necessary to protect the electronics from high temperatures. It also increases the average strength, decreases the average stress, and reduces stress variations, thus extending the component's life.
Temperature plays a crucial role in derating. As the temperature increases, the output power must be reduced linearly to protect the electronics. Similarly, at high altitudes, the atmospheric pressure and air density decrease, reducing the cooling effect of convection airflow, necessitating derating.
Derating is commonly applied to various electronic components, including resistors, diodes, transistors, LEDs, CPUs, and capacitors. It is also relevant when mounting power supplies in non-standard orientations, as the airflow for cooling may be compromised.
The amount of derating required is specified in the data sheet for each power supply or component. It includes a derating curve, which indicates how much the device can handle without sustaining damage at different temperatures.
