The breaker size for a 15 kVA 3-phase servo AVR starts at 32 A, 3-pole, because input current reaches about 31.2 A at low input (20.9 A at 415 V). Below: the math, the rule, and when to use 40 A.
How Do You Size the Breaker for a 15 kVA 3-Phase Servo AVR?
IEC 60364-4-43 requires design current (IB) ≤ breaker rating (In) ≤ cable capacity (IZ). For the current, use IB = 15,000 ÷ (√3 × V).
| Condition | Voltage | Input current | Next preferred breaker |
|---|---|---|---|
| Nominal supply | 415 V | 20.9 A | 25 A |
| Catalogue output voltage | 380 V | 22.8 A | 25 A |
| Lowest listed input, YIY SVC-3 | 278 V | 31.2 A | 32 A |
Breaker steps follow the IEC 60898 preferred values: 25, 32, 40 A. Output kVA stays constant, so input current rises as voltage falls. Losses aren’t included: if the datasheet input current at minimum input exceeds 32 A, use 40 A and rate the cable above it.
The SVC-3 15 kVA lists 278–433 V input, 380 V ±3% output (or customized), and its own MCB/MCCB. For 415 V output, get the input window in writing. Compare models on the three-phase stabilizers page, then run the 15 kVA three-phase comparison checks.
Frequently Asked Questions
Is a 25 A Breaker Ever Enough?
Only if your supply never drops below about 346 V, where 15 kVA draws exactly 25 A.
What Size Should the Output-Side Breaker Be?
Output sits at a steady 380 V, so full load is 22.8 A; 25 A covers it if the downstream cable is rated for it.
Can a Miniature Breaker Be Used on a 415V Supply?
Yes. IEC 60898-1 covers breakers up to 440 V between phases and 125 A. Ask your panel builder for the short-circuit rating at the installation point.
Final Thoughts
Start at 32 A; move to 40 A when losses push input current higher. Browse PRO-3 three-phase servo stabilizers for tighter-accuracy options.
