High Altitude Voltage and Current Derate Factors.


Most switchgear is tested with reference to Normal Temperature and Pressure at Sea Level (NTP) (25C, 298K, and 101.3 kPa, 1.013 mbar). An added safety factor allows normal use at altitudes up to 1000 m. For installation of switchgear, rated for up to 1000 m, at altitudes above 1000 m, the insulation level of external insulation under the standardized reference atmospheric conditions shall be determined by multiplying the insulation withstand voltages by a factor listed below. In addition, since the air density is less at greater altitudes, the capability of the surrounding air to disipate heat is reduced. This may require a rerating of the amperage of the device due to this decreased thermal regulation capability.

For the "Increase Column" multiply the maximum current/voltage of the applicaiton by this value to determine the switchgear current/voltage rating.
For the "Decrease Column" multiply the switchgear maximum current/voltage rating by this value to determine the maximum allowable current/voltage the switchgear can handle at the elevated level of the application.

Select here for Amperage Re-rating for high altitude applications
Select here for Voltage Re-rating for high altitude applications for power frequency, lightning impulse and phase-to-phase switching impulse voltages (M=1)MOST CONSERVATIVE
Select here for Voltage Re-rating for high altitude applications for longitudinal switching impulse voltage switching impulse voltages (M=0.9)
Select here for Voltage Re-rating for high altitude applications for phase-to-ground switching impulse voltage (M=0.75)

Notes:




Chart of High Altitude Amperage Derate Factors For High Altitude Applications.


Altitude in MetersAltitude in Feet Rated Amperage Increase
for eqpt rated 1000 m
Rated Eqpt Decrease
for eqpt rated 1000 m
Rated Amperage Increase
for eqpt. rated at Sea Level
Rated Eqpt Amps Decrease
for eqpt. rated at Sea Level
30.48 100 1.000 1.000 1.000 1.000
60.96 200 1.000 1.000 1.003 0.997
91.44 300 1.000 1.000 1.007 0.993
121.92 400 1.000 1.000 1.010 0.990
152.4 500 1.000 1.000 1.013 0.987
182.88 600 1.000 1.000 1.017 0.983
213.36 700 1.000 1.000 1.020 0.980
243.84 800 1.000 1.000 1.024 0.977
274.32 900 1.000 1.000 1.027 0.973
304.8 1000 1.000 1.000 1.031 0.970
335.28 1100 1.000 1.000 1.034 0.967
365.76 1200 1.000 1.000 1.038 0.963
396.24 1300 1.000 1.000 1.042 0.960
426.72 1400 1.000 1.000 1.045 0.957
457.2 1500 1.000 1.000 1.049 0.953
487.68 1600 1.000 1.000 1.053 0.950
518.16 1700 1.000 1.000 1.056 0.947
548.64 1800 1.000 1.000 1.060 0.943
579.12 1900 1.000 1.000 1.064 0.940
609.6 2000 1.000 1.000 1.068 0.937
640.08 2100 1.000 1.000 1.071 0.933
670.56 2200 1.000 1.000 1.075 0.930
701.04 2300 1.000 1.000 1.079 0.927
731.52 2400 1.000 1.000 1.083 0.923
762 2500 1.000 1.000 1.087 0.920
792.48 2600 1.000 1.000 1.091 0.917
822.96 2700 1.000 1.000 1.095 0.913
853.44 2800 1.000 1.000 1.099 0.910
883.92 2900 1.000 1.000 1.103 0.907
914.4 3000 1.000 1.000 1.107 0.903
944.88 3100 1.000 1.000 1.111 0.900
975.36 3200 1.000 1.000 1.115 0.897
1005.84 3300 1.000 1.000 1.119 0.893
1036.32 3400 1.003 0.997 1.124 0.890
1066.8 3500 1.007 0.993 1.128 0.887
1097.28 3600 1.010 0.990 1.132 0.883
1127.76 3700 1.013 0.987 1.136 0.880
1158.24 3800 1.017 0.983 1.141 0.877
1188.72 3900 1.020 0.980 1.145 0.873
1219.2 4000 1.024 0.977 1.149 0.870
1249.68 4100 1.027 0.973 1.154 0.867
1280.16 4200 1.031 0.970 1.158 0.863
1310.64 4300 1.034 0.967 1.163 0.860
1341.12 4400 1.038 0.963 1.167 0.857
1371.6 4500 1.042 0.960 1.172 0.853
1402.08 4600 1.045 0.957 1.176 0.850
1432.56 4700 1.049 0.953 1.181 0.847
1463.04 4800 1.053 0.950 1.186 0.843
1493.52 4900 1.056 0.947 1.190 0.840
1524 5000 1.060 0.943 1.195 0.837
1554.48 5100 1.064 0.940 1.200 0.833
1584.96 5200 1.068 0.937 1.205 0.830
1615.44 5300 1.071 0.933 1.210 0.827
1645.92 5400 1.075 0.930 1.215 0.823
1676.4 5500 1.079 0.927 1.220 0.820
1706.88 5600 1.083 0.923 1.224 0.817
1737.36 5700 1.087 0.920 1.230 0.813
1767.84 5800 1.091 0.917 1.235 0.810
1798.32 5900 1.095 0.913 1.240 0.807
1828.8 6000 1.099 0.910 1.245 0.803
1859.28 6100 1.103 0.907 1.250 0.800
1889.76 6200 1.107 0.903 1.255 0.797
1920.24 6300 1.111 0.900 1.261 0.793
1950.72 6400 1.115 0.897 1.266 0.790
1981.2 6500 1.119 0.893 1.271 0.787
2011.68 6600 1.124 0.890 1.277 0.783
2042.16 6700 1.128 0.887 1.282 0.780
2072.64 6800 1.132 0.883 1.287 0.777
2103.12 6900 1.136 0.880 1.293 0.773
2133.6 7000 1.141 0.877 1.299 0.770
2164.08 7100 1.145 0.873 1.304 0.767
2194.56 7200 1.149 0.870 1.310 0.763
2225.04 7300 1.154 0.867 1.316 0.760
2255.52 7400 1.158 0.863 1.322 0.757
2286 7500 1.163 0.860 1.327 0.753
2316.48 7600 1.167 0.857 1.333 0.750
2346.96 7700 1.172 0.853 1.339 0.747
2377.44 7800 1.176 0.850 1.345 0.743
2407.92 7900 1.181 0.847 1.351 0.740
2438.4 8000 1.186 0.843 1.357 0.737
2468.88 8100 1.190 0.840 1.364 0.733
2499.36 8200 1.195 0.837 1.370 0.730
2529.84 8300 1.200 0.833 1.376 0.727
2560.32 8400 1.205 0.830 1.383 0.723
2590.8 8500 1.210 0.827 1.389 0.720
2621.28 8600 1.215 0.823 1.395 0.717
2651.76 8700 1.220 0.820 1.402 0.713
2682.24 8800 1.224 0.817 1.408 0.710
2712.72 8900 1.230 0.813 1.415 0.707
2743.2 9000 1.235 0.810 1.422 0.703
2773.68 9100 1.240 0.807 1.429 0.700
2804.16 9200 1.245 0.803 1.435 0.697
2834.64 9300 1.250 0.800 1.442 0.693
2865.12 9400 1.255 0.797 1.449 0.690
2895.6 9500 1.261 0.793 1.456 0.687
2926.08 9600 1.266 0.790 1.463 0.683
2956.56 9700 1.271 0.787 1.471 0.680
2987.04 9800 1.277 0.783 1.478 0.677
3017.52 9900 1.282 0.780 1.485 0.673
3048 10000 1.287 0.777 1.493 0.670
3078.48 10100 1.293 0.773 1.500 0.667
3108.96 10200 1.299 0.770 1.508 0.663
3139.44 10300 1.304 0.767 1.515 0.660
3169.92 10400 1.310 0.763 1.523 0.657
3200.4 10500 1.316 0.760 1.531 0.653
3230.88 10600 1.322 0.757 1.538 0.650
3261.36 10700 1.327 0.753 1.546 0.647
3291.84 10800 1.333 0.750 1.554 0.643
3322.32 10900 1.339 0.747 1.563 0.640
3352.8 11000 1.345 0.743 1.571 0.637
3383.28 11100 1.351 0.740 1.579 0.633
3413.76 11200 1.357 0.737 1.587 0.630
3444.24 11300 1.364 0.733 1.596 0.627
3474.72 11400 1.370 0.730 1.604 0.623
3505.2 11500 1.376 0.727 1.613 0.620
3535.68 11600 1.383 0.723 1.622 0.617
3566.16 11700 1.389 0.720 1.631 0.613
3596.64 11800 1.395 0.717 1.639 0.610
3627.12 11900 1.402 0.713 --- ---
3657.6 12000 1.408 0.710 --- ---
3688.08 12100 1.415 0.707 --- ---
3718.56 12200 1.422 0.703 --- ---
3749.04 12300 1.429 0.700 --- ---
3779.52 12400 1.435 0.697 --- ---
3810 12500 1.442 0.693 --- ---
3840.48 12600 1.449 0.690 --- ---
3870.96 12700 1.456 0.687 --- ---
3901.44 12800 1.463 0.683 --- ---
3931.92 12900 1.471 0.680 --- ---
3962.4 13000 1.478 0.677 --- ---
3992.88 13100 1.485 0.673 --- ---
4023.36 13200 1.493 0.670 --- ---
4053.84 13300 1.500 0.667 --- ---
4084.32 13400 1.508 0.663 --- ---
4114.8 13500 1.515 0.660 --- ---
4145.28 13600 1.523 0.657 --- ---
4175.76 13700 1.531 0.653 --- ---
4206.24 13800 1.538 0.650 --- ---
4236.72 13900 1.546 0.647 --- ---
4267.2 14000 1.554 0.643 --- ---
4297.68 14100 1.563 0.640 --- ---
4328.16 14200 1.571 0.637 --- ---
4358.64 14300 1.579 0.633 --- ---
4389.12 14400 1.587 0.630 --- ---
4419.6 14500 1.596 0.627 --- ---
4450.08 14600 1.604 0.623 --- ---
4480.56 14700 1.613 0.620 --- ---
4511.04 14800 1.622 0.617 --- ---
4541.52 14900 1.631 0.613 --- ---
4572 15000 1.639 0.610 --- ---


Voltage Re-rating for high altitude applications for power frequency, lightning impulse and phase-to-phase switching impulse voltages (M=1)MOST CONSERVATIVE.


Altitude in MetersAltitude in Feet Rated Amperage Increase
for eqpt rated 1000 m
Rated Eqpt Decrease
for eqpt rated 1000 m
Rated Amperage Increase
for eqpt. rated at Sea Level
Rated Eqpt Amps Decrease
for eqpt. rated at Sea Level
100 328 1.000 1.000 1.012 0.988
200 656 1.000 1.000 1.025 0.976
300 984 1.000 1.000 1.037 0.964
400 1312 1.000 1.000 1.050 0.952
500 1640 1.000 1.000 1.063 0.940
600 1969 1.000 1.000 1.076 0.929
700 2297 1.000 1.000 1.090 0.918
800 2625 1.000 1.000 1.103 0.907
900 2953 1.000 1.000 1.117 0.895
1000 3281 1.000 1.000 1.131 0.885
1100 3609 1.012 0.988 1.145 0.874
1200 3937 1.025 0.976 1.159 0.863
1300 4265 1.037 0.964 1.173 0.853
1400 4593 1.050 0.952 1.187 0.842
1500 4921 1.063 0.940 1.202 0.832
1600 5249 1.076 0.929 1.217 0.822
1700 5577 1.090 0.918 1.232 0.812
1800 5906 1.103 0.907 1.247 0.802
1900 6234 1.117 0.895 1.263 0.792
2000 6562 1.131 0.885 1.278 0.782
2100 6890 1.145 0.874 1.294 0.773
2200 7218 1.159 0.863 1.310 0.763
2300 7546 1.173 0.853 1.326 0.754
2400 7874 1.187 0.842 1.342 0.745
2500 8202 1.202 0.832 1.359 0.736
2600 8530 1.217 0.822 1.376 0.727
2700 8858 1.232 0.812 1.393 0.718
2800 9186 1.247 0.802 1.410 0.709
2900 9514 1.263 0.792 1.427 0.701
3000 9843 1.278 0.782 1.445 0.692
3100 10171 1.294 0.773 1.463 0.684
3200 10499 1.310 0.763 1.481 0.675
3300 10827 1.326 0.754 1.499 0.667
3400 11155 1.342 0.745 1.518 0.659
3500 11483 1.359 0.736 1.536 0.651
3600 11811 1.376 0.727 1.555 0.643
3700 12139 1.393 0.718 1.575 0.635
3800 12467 1.410 0.709 1.594 0.627
3900 12795 1.427 0.701 1.614 0.620
4000 13123 1.445 0.692 1.634 0.612
4100 13451 1.463 0.684 1.654 0.605
4200 13780 1.481 0.675 1.674 0.597
4300 14108 1.499 0.667 1.695 0.590
4400 14436 1.518 0.659 1.716 0.583
4500 14764 1.536 0.651 1.737 0.576
4600 15092 1.555 0.643 1.758 0.569
4700 15420 1.575 0.635 1.780 0.562
4800 15748 1.594 0.627 1.802 0.555
4900 16076 1.614 0.620 1.824 0.548
5000 16404 1.634 0.612 1.847 0.541
5100 16732 1.654 0.605 1.870 0.535
5200 17060 1.674 0.597 1.893 0.528
5300 17388 1.695 0.590 1.916 0.522
5400 17717 1.716 0.583 1.940 0.516
5500 18045 1.737 0.576 1.964 0.509
5600 18373 1.758 0.569 1.988 0.503
5700 18701 1.780 0.562 2.013 0.497
5800 19029 1.802 0.555 2.037 0.491
5900 19357 1.824 0.548 2.063 0.485
6000 19685 1.847 0.541 2.088 0.479


Voltage Re-rating for high altitude applications for longitudinal switching impulse voltage switching impulse voltages (M=0.9).


Altitude in MetersAltitude in Feet Rated Amperage Increase
for eqpt rated 1000 m
Rated Eqpt Decrease
for eqpt rated 1000 m
Rated Amperage Increase
for eqpt. rated at Sea Level
Rated Eqpt Amps Decrease
for eqpt. rated at Sea Level
100 328 1.000 1.000 1.011 0.989
200 656 1.000 1.000 1.022 0.978
300 984 1.000 1.000 1.034 0.967
400 1312 1.000 1.000 1.045 0.957
500 1640 1.000 1.000 1.057 0.946
600 1969 1.000 1.000 1.069 0.936
700 2297 1.000 1.000 1.080 0.926
800 2625 1.000 1.000 1.092 0.915
900 2953 1.000 1.000 1.104 0.905
1000 3281 1.000 1.000 1.117 0.895
1100 3609 1.011 0.989 1.129 0.886
1200 3937 1.022 0.978 1.142 0.876
1300 4265 1.034 0.967 1.154 0.866
1400 4593 1.045 0.957 1.167 0.857
1500 4921 1.057 0.946 1.180 0.847
1600 5249 1.069 0.936 1.193 0.838
1700 5577 1.080 0.926 1.207 0.829
1800 5906 1.092 0.915 1.220 0.820
1900 6234 1.104 0.905 1.233 0.811
2000 6562 1.117 0.895 1.247 0.802
2100 6890 1.129 0.886 1.261 0.793
2200 7218 1.142 0.876 1.275 0.784
2300 7546 1.154 0.866 1.289 0.776
2400 7874 1.167 0.857 1.303 0.767
2500 8202 1.180 0.847 1.318 0.759
2600 8530 1.193 0.838 1.333 0.750
2700 8858 1.207 0.829 1.347 0.742
2800 9186 1.220 0.820 1.362 0.734
2900 9514 1.233 0.811 1.377 0.726
3000 9843 1.247 0.802 1.393 0.718
3100 10171 1.261 0.793 1.408 0.710
3200 10499 1.275 0.784 1.424 0.702
3300 10827 1.289 0.776 1.440 0.695
3400 11155 1.303 0.767 1.456 0.687
3500 11483 1.318 0.759 1.472 0.679
3600 11811 1.333 0.750 1.488 0.672
3700 12139 1.347 0.742 1.505 0.665
3800 12467 1.362 0.734 1.521 0.657
3900 12795 1.377 0.726 1.538 0.650
4000 13123 1.393 0.718 1.555 0.643
4100 13451 1.408 0.710 1.573 0.636
4200 13780 1.424 0.702 1.590 0.629
4300 14108 1.440 0.695 1.608 0.622
4400 14436 1.456 0.687 1.626 0.615
4500 14764 1.472 0.679 1.644 0.608
4600 15092 1.488 0.672 1.662 0.602
4700 15420 1.505 0.665 1.680 0.595
4800 15748 1.521 0.657 1.699 0.589
4900 16076 1.538 0.650 1.718 0.582
5000 16404 1.555 0.643 1.737 0.576
5100 16732 1.573 0.636 1.756 0.569
5200 17060 1.590 0.629 1.776 0.563
5300 17388 1.608 0.622 1.795 0.557
5400 17717 1.626 0.615 1.815 0.551
5500 18045 1.644 0.608 1.836 0.545
5600 18373 1.662 0.602 1.856 0.539
5700 18701 1.680 0.595 1.877 0.533
5800 19029 1.699 0.589 1.897 0.527
5900 19357 1.718 0.582 1.918 0.521
6000 19685 1.737 0.576 1.940 0.516


Voltage Re-rating for high altitude applications for phase-to-ground switching impulse voltage (M=0.75).


Altitude in MetersAltitude in Feet Rated Amperage Increase
for eqpt rated 1000 m
Rated Eqpt Decrease
for eqpt rated 1000 m
Rated Amperage Increase
for eqpt. rated at Sea Level
Rated Eqpt Amps Decrease
for eqpt. rated at Sea Level
100 328 1.000 1.000 1.009 0.991
200 656 1.000 1.000 1.019 0.982
300 984 1.000 1.000 1.028 0.973
400 1312 1.000 1.000 1.037 0.964
500 1640 1.000 1.000 1.047 0.955
600 1969 1.000 1.000 1.057 0.946
700 2297 1.000 1.000 1.067 0.938
800 2625 1.000 1.000 1.076 0.929
900 2953 1.000 1.000 1.086 0.921
1000 3281 1.000 1.000 1.096 0.912
1100 3609 1.009 0.991 1.107 0.904
1200 3937 1.019 0.982 1.117 0.895
1300 4265 1.028 0.973 1.127 0.887
1400 4593 1.037 0.964 1.138 0.879
1500 4921 1.047 0.955 1.148 0.871
1600 5249 1.057 0.946 1.159 0.863
1700 5577 1.067 0.938 1.169 0.855
1800 5906 1.076 0.929 1.180 0.847
1900 6234 1.086 0.921 1.191 0.840
2000 6562 1.096 0.912 1.202 0.832
2100 6890 1.107 0.904 1.213 0.824
2200 7218 1.117 0.895 1.224 0.817
2300 7546 1.127 0.887 1.236 0.809
2400 7874 1.138 0.879 1.247 0.802
2500 8202 1.148 0.871 1.259 0.794
2600 8530 1.159 0.863 1.270 0.787
2700 8858 1.169 0.855 1.282 0.780
2800 9186 1.180 0.847 1.294 0.773
2900 9514 1.191 0.840 1.306 0.766
3000 9843 1.202 0.832 1.318 0.759
3100 10171 1.213 0.824 1.330 0.752
3200 10499 1.224 0.817 1.342 0.745
3300 10827 1.236 0.809 1.355 0.738
3400 11155 1.247 0.802 1.367 0.731
3500 11483 1.259 0.794 1.380 0.725
3600 11811 1.270 0.787 1.393 0.718
3700 12139 1.282 0.780 1.406 0.711
3800 12467 1.294 0.773 1.419 0.705
3900 12795 1.306 0.766 1.432 0.698
4000 13123 1.318 0.759 1.445 0.692
4100 13451 1.330 0.752 1.458 0.686
4200 13780 1.342 0.745 1.472 0.679
4300 14108 1.355 0.738 1.485 0.673
4400 14436 1.367 0.731 1.499 0.667
4500 14764 1.380 0.725 1.513 0.661
4600 15092 1.393 0.718 1.527 0.655
4700 15420 1.406 0.711 1.541 0.649
4800 15748 1.419 0.705 1.555 0.643
4900 16076 1.432 0.698 1.570 0.637
5000 16404 1.445 0.692 1.584 0.631
5100 16732 1.458 0.686 1.599 0.625
5200 17060 1.472 0.679 1.614 0.620
5300 17388 1.485 0.673 1.629 0.614
5400 17717 1.499 0.667 1.644 0.608
5500 18045 1.513 0.661 1.659 0.603
5600 18373 1.527 0.655 1.674 0.597
5700 18701 1.541 0.649 1.690 0.592
5800 19029 1.555 0.643 1.705 0.586
5900 19357 1.570 0.637 1.721 0.581
6000 19685 1.584 0.631 1.737 0.576


Notes:
#1. For devices used in switchgear assemblies, standards covering the specific devices should be used to determine the specific altitude correction factor.
#2. Currently IEEE and ANSI are re-evaluating these derating factors and, therefore, the values listed above are subject to change without notice.
#3. When the above data disagrees with actual manufacturer data, always default to actual manufacturer data.
#4. These values are for educational purposes only.
Due to the wide range of circuit applications, the author assumes no responsibility for the application of these values.


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