Tubular heaters absorb moisture

Tubular Heater Drying Instructions

The material inside any tubular heater (aka 'calrod') provides excellent electrical insulation, but has the unfortunate behavior of also absorbing moisture from the humidity in the air.  Even though the end of the tubular heater might appear to be sealed, it is not a true hermetic seal.  During shipping, storage or even times of non-use, tubular heaters can absorb the moisture from the air and it may collect inside the metal sheath.  How quickly this happens is a function of the ambient conditions in which it is stored and the amount of time that it is subjected to those conditions.  If enough moisture collects inside the sheath, it could cause circuit breakers to trip when the heater is first energized.  All Eichenauer tubular heaters are 100% tested for insulation resistance at final inspection so that you can be assured that there is no moisture in them when shipped from our factory.  During normal use, the operation of the heater prevents moisture absorption.

Before installation or after long periods of un-use or storage, it is a good habit to perform an insulation resistance test to check for the presence of moisture.  This is done with a megohm meter, commonly known as a 'Megger' at room temperature.  Each tubular heater should not be less than 20MΩ when tested with a 500VDC megger between the terminal and the sheath.  If several tubes are bussed or wired together, this value can be reduced.  If there are multiple groups of connected tubes, each group should be checked with the megger.  In the event of a low insulation resistance value, the heater should be dried before use.

The preferred method of drying is in an oven at 110°C (230°F) or greater, but not to exceed 177°C (350°F) for a minimum of 4 hours or until an acceptable insulation resistance value is achieved.  Any lead wires, thermostats or other hardware not rated for this temperature need to be removed.