ATS Panel Rating Calculator
Size the ATS to carry the full site load safely.
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ATS Panel Rating Calculator by TheCalcTools
How the ATS Panel Rating Calculator works
Enter the site load and power factor.
If a generator is installed, enter its kVA: the ATS must also carry its full-load current.
The ATS rating is the next standard size above the larger of the two.
The formula
Worked example
Using the default values shown in the calculator:
| Site load (kW) | 25 |
|---|---|
| Power factor | 0.85 |
| Voltage (V, line) | 400 |
| Generator rating (kVA, optional, 0 to skip) | 40 |
| Margin (%) | 25 % |
- Load current = 25,000 ÷ (√3 × 400 × 0.85) × 1.25 = 53.1 A.
- Generator 40 kVA draws 57.7 A. ATS rating: 63 A.
Result:
| Load current with margin (A) | 53.1 |
|---|---|
| Generator full-load current (A) | 57.7 |
| Governing current (A) | 57.7 |
| ATS rating (A) | 63 |
Frequently asked questions
3-pole or 4-pole ATS?
Use 4-pole switching of the neutral where required by your earthing system or to avoid neutral-current issues; confirm with your design standard.
Is the ATS short-circuit rated?
Check its withstand and closing rating against the prospective fault level. Many ATS units need an upstream breaker for protection.
Sources and further reading
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This calculator gives estimates for planning only. Electrical installations must be designed, checked and carried out by qualified personnel following local codes and the equipment manufacturer's data. Never rely on this result alone for safety-critical decisions. See our disclaimer.