A good insulating material will be free of impurities that may act as internal conductors. When it comes to glass and porcelain, both can be very pure     early glass insulators, we often see impurities  in the glass due to poor quality control. Fortunately, when the glass completely seals  any electrical problems. This is especially true in low voltage applications such as telegraph, telephone, and signaling.


The porosity of an insulating material is important when it comes to keeping out foreign material while in use. Dirt, moisture, and other contaminants could quickly cause a porous material to fail. Glass is very non-porous while porcelain usually has a glass glaze over the outside to completely seal it.


Lastly, it is important for insulator material to be both mechanically and electrically stable with changes in temperature. Depending on where an insulator is used,  change quickly. Here in Northern Utah we see outdoor temperatures that vary from -35° F to +105° F. Other locations can have even greater variations. Temperature             have to be able to handle both. Glass and 


There are a lot more details that go into the selection of materials used for electrical insulators. This article has only touched on the most important considerations for   went into the early decisions as to what to use for insulating wires. Once again, this is just another interesting and educational aspect of our hobby.


Have fun learning  “BLOCK HEAD” looking for BLOCK TYPE TELEGRAPH INSULATORS


CD 1000 good condition:any color but especially Amber or Light Purple CD 1001 / CD 1002 / CD 1003 / CD 1004 / CD1005 / CD 1006 CD 1007 / CD 1008 / CD 1010 – CD 1017


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CD 127.4 Good color / character September 2018


CD 131 TILLOTSON Good Shape CD 132 Good color / character


CD 206.5 Harloe CLAW Great Condition STEPHEN DRAKE


StephenD13@hotmail.com / 828-551-6970 13


Screw in Glass


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