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608.8 Electrical System Efficiency
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Electrical systems shall comply with Section 608.8.1.
Distribution transformers installed on the load side of the service disconnecting means shall comply with the provisions of Tables 608.8.1.1(1), 608.8.1.1(2) and 608.8.1.1(3), and the Energy Policy Act of 2005 as applicable.
Exception:
The following transformers are exempt from the efficiency standards of Section 608.8.1.1:
- Transformers not covered by the Energy Policy Act of 2005.
- Transformers for special purpose applications, and not used in general purpose applications.
- Transformers with multiple voltage taps where the highest tap is not less than 20 percent more than the lowest tap.
- Drive transformers, rectifier transformers, auto-transformers, uninterruptible power supply transformers, impedance transformers, regulating transformers, sealed and nonventilating transformers, machine tool transformers, welding transformers, grounding transformers, and testing transformers.
| SINGLE PHASE | THREE PHASE | ||
| kVA Rating | Minimum Efficiency (%) |
kVA Rating | Minimum Efficiency (%) |
| 15 | 97.7 | 15 | 97.0 |
| 25 | 98.0 | 30 | 97.5 |
| 37.5 | 98.2 | 45 | 97.7 |
| 50 | 98.3 | 75 | 98.0 |
| 75 | 98.5 | 112.5 | 98.2 |
| 100 | 98.6 | 150 | 98.3 |
| 167 | 98.7 | 225 | 98.5 |
| 250 | 98.8 | 300 | 98.6 |
| 333 | 98.9 | 500 | 98.7 |
| — | — | 750 | 98.8 |
| — | — | 1000 | 98.9 |
- All efficiency values for low-voltage transformers are at 35 percent of nameplate-rated load, determined in accordance with the DOE test procedure. 10 CFR Part 431, Sub-part K, Appendix A.
| SINGLE PHASE | THREE PHASE | ||||||
| kVA Rating | 20-45 kV BIL Minimum Efficiency (%) |
46-95 kV BIL Minimum Efficiency (%) |
>96 kV BIL Minimum Efficiency (%) |
kVA Rating | 20-45 kV BIL Minimum Efficiency (%) |
46-95 kV BIL Minimum Efficiency (%) |
>96 kV BIL Minimum Efficiency (%) |
| 15 | 98.10 | 97.86 | — | 15 | 97.50 | 97.18 | — |
| 25 | 98.33 | 98.12 | — | 30 | 97.90 | 97.63 | — |
| 37.5 | 98.49 | 98.30 | — | 45 | 98.10 | 97.86 | — |
| 50 | 98.60 | 98.42 | — | 75 | 98.33 | 98.12 | — |
| 75 | 98.73 | 98.57 | 98.53 | 112.5 | 98.49 | 98.30 | — |
| 100 | 98.82 | 98.67 | 98.63 | 150 | 98.60 | 98.42 | — |
| 167 | 98.96 | 98.83 | 98.80 | 225 | 98.73 | 98.57 | 98.53 |
| 250 | 99.07 | 98.95 | 98.91 | 300 | 98.82 | 98.67 | 98.63 |
| 333 | 99.14 | 99.03 | 98.99 | 500 | 98.96 | 98.83 | 98.80 |
| 500 | 99.22 | 99.12 | 99.09 | 750 | 99.07 | 98.95 | 98.91 |
| 667 | 99.27 | 99.18 | 99.15 | 1000 | 99.14 | 99.03 | 98.99 |
| 833 | 99.31 | 99.23 | 99.20 | 1500 | 99.22 | 99.12 | 99.09 |
| — | — | — | — | 2000 | 99.27 | 99.18 | 99.15 |
| — | — | — | — | 2500 | 99.31 | 99.23 | 99.20 |
BIL = Basic impulse insulation level.
- All efficiency values for medium-voltage transformers are at 50 percent of nameplate-rated load, determined in accordance with the DOE test procedure. 10 CFR Part 431, Sub-part K, Appendix A.
| SINGLE PHASE | THREE PHASE | ||
| kVA Rating | Minimum Efficiency (%) |
kVA Rating | Minimum Efficiency (%) |
| 10 | 98.62 | 15 | 98.36 |
| 15 | 98.76 | 30 | 98.62 |
| 25 | 98.91 | 45 | 98.76 |
| 37.5 | 99.01 | 75 | 98.91 |
| 50 | 99.08 | 112.5 | 99.01 |
| 75 | 99.17 | 150 | 99.08 |
| 100 | 99.23 | 225 | 99.17 |
| 167 | 99.25 | 300 | 99.23 |
| 250 | 99.32 | 500 | 99.25 |
| 333 | 99.36 | 750 | 99.32 |
| 500 | 99.42 | 1000 | 99.36 |
| 667 | 99.46 | 1500 | 99.42 |
| 883 | 99.49 | 2000 | 99.46 |
| — | — | 2500 | 99.49 |
- All efficiency values for medium-voltage transformers are at 50 percent of nameplate-rated load, determined in accordance with the DOE test procedure. 10 CFR Part 431, Sub-part K, Appendix A.
The voltage drop in feeder conductors shall not exceed 1.5 percent at design load.
The voltage drop in branch circuit conductors shall not exceed 1.5 percent at design load.
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