The standard rod gap uses two long rods (usually square in cross section, but round can be used) either 1/2 or 5/8" in diameter. The end is cut perpendicular. The tables usually show a rod cross diameter of 1.27 cm, which reflects their British/American origin. Rod gap measurements are typically considered accurate to ±8%, when corrected for humidity, temperature, and density.
The rods may be 15 to 75 cm long and the gap will be from 2 to 200 cm. For impulse measurements, IEC and IEEE recommend horizontal mounting of the rod gap on insulators at 1.5 to 2 times the gap spacing above ground.
Copyright 1998, Jim Lux / rodgap.htm / 8 March 1998 / Back to HV Home / Back to home page / Mail to Jim