High Voltage Ratings of Silicone Rubber - John Dunn, Consultant, Ambertec, P.E., P.C.

Sometimes, when we look way back in time, we find the most useful things. I refer to this application note:

 
I had the pleasure of meeting Jim Hawkins back in 1986. It was both an enjoyable and educational experience. His key point to me that day was from the CDS-2081 document that the volts per mil ratings of silicone rubber or RTV is not a constant as the thickness of the RTV is varied. 

Extracting from the CDS-2081, one may come up with the following:  

 
From this we may examine voltage support capability and derated voltage stress as follows:

 
I have heard it said as a common colloquialism that RTV is "good for five-hundred volts per mil".

General Electric has long since left the RTV business, but RTV is still obtainable elsewhere and the data sheet for that material shows 515 volts per mil rating at 1.9mm thickness. Just look out though if you are working at some other, different thickness.

If you'd like to put on a fireworks show, then go ahead with the colloquialism , but if you want to make a reliable high voltage device using RTV as your supporting dielectric, then look more closely at this chart.

Comments

[Marty Kanner]

John,
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As you reminded us all, RTV has been noted to have a very high dielectric stength for many years. However the newer kid on the block is Kapton and that material will withstand soldering iron temperatures and a breakdown raing in the area of 2000 volts/mil. I've been using it successfully for a number of years now. I also refer you to one of my comments to your blog regarding an application to heat sinking.

[furnace spares]

High temperature silicone is used in a host of applications where sealants, adhesives, or insulators are needed which do not degrade or deform when exposed to high heat.