How are the minimum seal length and the minimum outside diameter of the seal determined?

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The minimum seal length is a function of the pressure differential, leak rate, conductor dimensions, voltage and operating temperature range. Most seal lengths are from 0.30 inch (7,7mm) to 1 inch (25mm) or more. Longer seal lengths typically have higher pressure ratings. Seal thickness can be as small as 0.100 inch or less for low pressure (less than 10 bar) or ambient temperature (80º C maximum).

1000 bar will require a 25mm length or more. In order to bond properly to wire insulation, we recommend lengths typically between 12 and 25 mm where possible, though seals as thin as 0.100 inches may be available for low pressure and ambient temperature applications.

The outside diameter of the seal is determined by the number and size of conductors, any electrical shielding, whether the housing is metal or plastic and the size and type of the o-ring seal, if an o-ring is used. Small wires sizes of #22 AWG (0,78mm) or smaller can be spaced on 0.050 inch (1,3mm) centers. Larger wire conductors will require wider spacing for both electrical and mechanical reliability from 2-3 mm or more.

High pressures of over 30 bar, temperatures between over 80º C up to 200º C or voltages over 1000 Vac may also require slightly more spacing. Electrical shielding (sheathing) or braid will also increase the seal diameter, especially if the shielding is to be carried through the seal. Essentially, the shield will take up the same space as a ring of individual wires around the center wire.