Table
Transformer Fault Current Multipliers by Percent Z
Transformer Fault Current Multipliers by Percent Z reference with assumptions and boundary notes.
Reference boundary
Transformer secondary fault-current estimate only. It does not determine equipment AIC/SCCR, utility contribution, motor contribution, or protective-device adequacy.
Reference table
Estimate transformer secondary fault current from full-load current and transformer impedance percent.
| Transformer kVA | Secondary V | Impedance (%) | Full-load A | Approx. current (A) | Boundary |
|---|---|---|---|---|---|
| 45 | 600 | 5 | 43.3 | 866 | transformer-only approximation; utility source impedance and motor contribution are not included |
| 75 | 600 | 5 | 72.2 | 1443 | transformer-only approximation; utility source impedance and motor contribution are not included |
| 150 | 600 | 5 | 144.3 | 2887 | transformer-only approximation; utility source impedance and motor contribution are not included |
| 300 | 600 | 5.75 | 288.7 | 5020 | transformer-only approximation; utility source impedance and motor contribution are not included |
| 500 | 600 | 5.75 | 481.1 | 8367 | transformer-only approximation; utility source impedance and motor contribution are not included |
| 75 | 208 | 5 | 208.2 | 4164 | transformer-only approximation; utility source impedance and motor contribution are not included |
| 150 | 208 | 5 | 416.4 | 8327 | transformer-only approximation; utility source impedance and motor contribution are not included |
Use notes
- Use this table for preliminary reference and arithmetic checks only.
- Confirm equipment ratings, product markings, installation conditions, utility requirements, and the local authority requirements before design or field use.