Accurate thermal dissipation calculations are critical for safe, efficient panelboard design under IEC standards. Understanding heat generation and removal ensures compliance and longevity.
This article explores the “Thermal Dissipation in Panelboards Calculator – IEC,” detailing formulas, tables, and real-world applications for engineers and designers.
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- Calculate thermal dissipation for a 100 A panelboard with 10 circuit breakers.
- Determine heat loss in a 250 A panelboard with mixed load types.
- Estimate panelboard temperature rise for a 400 A distribution board.
- Compute total heat dissipation for a panelboard with 15 MCCBs rated at 63 A each.
Comprehensive Tables of Thermal Dissipation Values for Panelboards (IEC)
| Component Type | Rated Current (A) | Typical Power Loss (W) | Thermal Dissipation Factor (W/A) | Reference Standard |
|---|---|---|---|---|
| Molded Case Circuit Breaker (MCCB) | 16 | 3.2 | 0.20 | IEC 60947-2 |
| MCCB | 63 | 12.6 | 0.20 | IEC 60947-2 |
| Miniature Circuit Breaker (MCB) | 10 | 1.0 | 0.10 | IEC 60898-1 |
| MCB | 32 | 3.2 | 0.10 | IEC 60898-1 |
| Busbar (Copper, 10 mm²) | N/A | 0.5 (per meter) | N/A | IEC 60439-1 |
| Contactor (AC-3 Duty) | 40 | 8.0 | 0.20 | IEC 60947-4-1 |
| Thermal Relay | 20 | 2.0 | 0.10 | IEC 60947-5-1 |
| Panelboard Type | Rated Current (A) | Typical Heat Dissipation (W) | Ambient Temperature (°C) | Reference |
|---|---|---|---|---|
| Distribution Panelboard (Indoor) | 100 | 50 | 35 | IEC 61439-1 |
| Motor Control Center (MCC) | 250 | 120 | 40 | IEC 61439-2 |
| Lighting Panelboard | 63 | 25 | 30 | IEC 61439-1 |
| Control Panelboard (Enclosed) | 125 | 60 | 35 | IEC 61439-1 |
Fundamental Formulas for Thermal Dissipation in Panelboards (IEC)
Thermal dissipation in panelboards is primarily the heat generated by electrical components during operation. Calculating this heat accurately is essential for thermal management and compliance with IEC standards.
1. Total Thermal Dissipation (Qtotal)
The total heat dissipation of a panelboard is the sum of the heat losses of all individual components:
- Qtotal: Total thermal dissipation (Watts, W)
- Qi: Heat dissipation of the i-th component (W)
- Ii: Rated current of the i-th component (Amperes, A)
- ki: Thermal dissipation factor for the i-th component (W/A)
The thermal dissipation factor (ki) depends on the component type and is typically provided by IEC standards or manufacturer datasheets.
2. Heat Dissipation of Busbars (Qbusbar)
Heat loss in busbars is mainly due to resistive losses and can be approximated by:
- I: Current through the busbar (A)
- R: Resistance per unit length of busbar (Ω/m)
- L: Length of busbar (m)
Resistance (R) depends on the busbar material and cross-sectional area, calculated as:
- ρ: Resistivity of the material (Ω·m), e.g., copper ≈ 1.68 × 10-8 Ω·m
- A: Cross-sectional area of busbar (m²)
3. Temperature Rise Estimation (ΔT)
Temperature rise inside the panelboard enclosure can be estimated by:
- ΔT: Temperature rise above ambient (°C)
- Qtotal: Total heat dissipation (W)
- h: Heat transfer coefficient (W/m²·K), depends on convection and radiation
- Asurface: Surface area of the panelboard enclosure (m²)
Typical values for h range from 5 to 25 W/m²·K depending on ventilation and enclosure design.
4. Derating Factor for Ambient Temperature (kamb)
IEC standards require derating of components based on ambient temperature:
- Iderated: Derated current (A)
- Irated: Rated current at 25°C (A)
- kamb: Ambient temperature correction factor (dimensionless)
Values of kamb are provided in IEC 60947 and IEC 61439 series, typically decreasing as ambient temperature rises.
Real-World Application Examples of Thermal Dissipation in Panelboards (IEC)
Example 1: Calculating Total Thermal Dissipation for a 100 A Panelboard
A distribution panelboard contains the following components:
- 5 MCCBs rated at 16 A
- 3 MCCBs rated at 63 A
- 1 Busbar, copper, 1 meter length, 10 mm² cross-section
Calculate the total thermal dissipation (Qtotal) assuming the following thermal dissipation factors:
- MCCB 16 A: 0.20 W/A
- MCCB 63 A: 0.20 W/A
- Busbar resistance: R = ρ / A = 1.68 × 10-8 / (10 × 10-6) = 0.00168 Ω/m
Step 1: Calculate heat dissipation for MCCBs
Step 2: Calculate heat dissipation for busbar
Step 3: Calculate total thermal dissipation
This total heat dissipation must be managed by the panelboard enclosure design to prevent overheating.
Example 2: Estimating Temperature Rise in a 250 A Motor Control Center (MCC)
A motor control center rated at 250 A has a total heat dissipation of 120 W. The enclosure surface area is 1.5 m², and the heat transfer coefficient is estimated at 10 W/m²·K. Calculate the temperature rise above ambient.
Step 1: Use the temperature rise formula:
Step 2: Interpret the result
The panelboard temperature will rise approximately 8°C above ambient. If ambient temperature is 40°C, the internal temperature will be 48°C, which must be checked against component temperature ratings and derating factors.
Additional Technical Considerations for Thermal Dissipation Calculations
- Ventilation and Cooling: Natural convection, forced ventilation, or air conditioning significantly affect heat transfer coefficient (h).
- Enclosure Material: Thermal conductivity of enclosure materials (steel, aluminum, plastic) influences heat dissipation efficiency.
- Component Loading: Actual load currents may differ from rated currents, affecting real heat generation.
- Ambient Conditions: Humidity, altitude, and ambient temperature variations impact thermal performance and derating.
- IEC Standards Compliance: IEC 61439 series provides detailed guidelines for thermal testing and verification of panelboards.
For precise thermal management, engineers should combine calculation methods with thermal imaging and testing during panelboard commissioning.
Authoritative References and Further Reading
- IEC 61439-1: Low-voltage switchgear and controlgear assemblies – Part 1: General rules
- IEC 60947-2: Low-voltage switchgear and controlgear – Circuit-breakers
- IEC 60898-1: Circuit-breakers for overcurrent protection for household and similar installations
- Eaton MCCB Technical Data and Thermal Dissipation