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Sphere Gap Breakdown Voltage Tables

The following two tables give the breakdown voltages for a standard sphere gap of the specified sphere size and spacing. The standard accuracy is ±3% for gaps less than half the sphere diameter and 5% for gaps larger than that. The first table is for a gap with one terminal grounded, typically a vertical gap. There are two columns for each sphere size depending on whether it is a positive or negative impulse. The second table is for a gap with both terminals at HV. The values from these tables will need to be corrected for current atmospheric conditions, particularly humidity.

A -> AC, DC, either polarity and full negative standard impulse voltages (one sphere grounded)
B -> positive polarity standard impulse voltages and impulse voltages with long tails (either polarity)

Gap Spacing551010151525255050100100150150200200
ABABABABABABABAB
0.517.417.416.916.816.916.9
1323231.731.731.431.431.231.4
1.544.745.544.745.144.745.144.744.7
257.558585858585858
2.571.571.571.571.571.571.571.571.5
38585858585858585
3.595.596979797979797
4106108108110110110110110
5123127127132135136136136
7.5181187195196199199
10257268259259262262262262262262
12.5277294315317
15309331367974383384384384384384
17.5336362413425
20452472500500500500500500
25520545605610
30575610700715730735735740
35725755785800
40862885940950960965
45925965
50100010201110113011601170
75121012601420146015101590
10018701900

 

symmetrical sphere gaps 20deg C, 760 torr, either polarity impulse, AC, DC
spacings <0.5D Accuracy +/- 3% ; spacings >=0.5D accuracy +/- 5%

gap (cm)510152550100150200
0.517.516.916.5
132.231.631.331
1.546.145.845.545
258.359.359.259
2.569.472.472.973
379.384.985.886
4107111113112
5128134138138137137137
8177194207214
10248263266267267
12286309
14320353
16352394
18452
20495504511511
25558613628632
30744741746
35812848860
40902950972
50107011401180
60121013201380
7014901560
8016401730
901900
1002050

Copyright 1998, Jim Lux / spherev.htm / 8 March 1998 / Back to HV Home / Back to home page / Mail to Jim