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Glossary of Technical Terms

Conductivity or Resistivity -

(inversely related terms) Measures the current-carrying ability of an insulating material—as if treating the insulating material as a conductor. Measured by ASTM D-257.

Corona or Partial Discharge -

Low-level passage of high-voltage current through a gas, usually air, due to ionization. In air, corona creates highly active ozone, which can cause severe chemical damage to materials nearby. May be audible (a hiss) and visible (a blue glow).

Corona Resistance or Voltage Endurance -

(similar terms)—Ability of the insulating material to withstand damage caused by voltages (usually high) applied in use.

Dielectric Strength -

Voltage required to puncture the material. May be direct current or alternating current (DC or AC), at many test conditions. Often measured by ASTM Standard D-149.

Dielectric Constant or Permittivity -

(similar terms)—Measures the capacity of the material to store energy. Generally, the lower the better, since it also determines how much AC leakage current can flow through the material, and how voltage stress is distributed in an insulation system. Often measured by ASTM D-150.

Dissipation Factor -

Relates to energy that is lost in the insulating material due to AC current flow (capacitive current). Usually measured by ASTM D-150.

Impulse Dielectric Strength -

Ability to resist a very short pulse of high voltage, such as a lightning strike. Measured by ASTM D-3426.

Breaking Elongation -

Amount the material will stretch under tensile stress before yielding and breaking under tension. Measured by ASTM D-828.

Initial Tear Resistance -

Ability of the material to resist tearing when a force is applied to tear a well-cut edge of the material. Usually tested by ASTM D-1004.

Power Frequency -

Frequency of the sine-wave power in Hertz (written Hz) (formerly cycles per second). Usually 60 Hz in the United States and parts of Asia, 50 Hz in Europe and parts of Asia, etc.

Harmonics -

Multiples of the power frequency, e.g., 120 Hz, 180 Hz, 600 Hz, on a 60 Hz power system. The higher the harmonic content, the higher the rate of damage to the equipment if corona (partial discharge) occurs.

Tear Propagation Strength -

Measures the ease with which a cut or tear that already exists can be further extended. Usually measured by TAPPI Test T-414, the Elmendorf Test.

Tensile Strength -

The ability of the insulating material to resist straight-line pulling forces without breaking. Usually measured by ASTM D-828.

Thermal Conductivity -

Measures the speed with which heat is transmitted through the material. The higher the thermal conductivity of the insulation, the easier it is to cool the electrical equipment by transferring heat to other parts of the machine, or to the air. Usually measured by ASTM D-1674.

Temperature Conversions and Dimension Conversions 

Degrees C 

Degrees F 

Inches 

mm 

mils 

100 

212 

.002 

.051 

110 

230 

.003 

.076 

120 

248 

.004 

.102 

130 

266 

.005 

.127 

140 

284 

.006 

.152 

150 

302 

.007 

.178 

160 

320 

.008 

.203 

170 

338 

.009 

.229 

180 

356 

.010 

.254 

10 

190 

374 

.015 

.381 

15 

200 

392 

.020 

.508 

20 

210 

410 

.025 

.635 

25 

220 

428 

.030 

.762 

30 

230 

446 

.050 

1.27 

50 

240 

464 

.100 

2.54 

100 

250 

482 

.200 

5.08 

200 

260

500

.300

7.62

300

 

 

.400 

10.2 

400