The dielectric used in the production of all mineral insulated heating elements magnesium oxide is hydroscopic. On completion, the heating elements will be sealed against ingress of moisture and while we set our pass/fail level for inspection testing at 100 megohms in practice, elements leaving the works will be infinity.
One of the seal techniques we employ is a silicone-based fluid and does not give a totally hermetic seal. Over extended period in stock the I.R. value will reduce gradually, if elements fall below 1 meg-ohm, we recommend that the element should be dried at a temperature of 250 to 300°c for 3 to 4 hours before use. This will remove the moisture contents of the insulant and the I.R. value will quickly restore to previous level.
All products must be kept in a clean dry area and protected from dust and dampness in order to ensure the correct operation of this equipment.