Page 299 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Enclosures:
Immersion heater enclosures, casings, have normally been made from aluminum since the middle of the 20th
Century. Plastic enclosures have become more popular because of plastic‘s moldability but have been of inferior
quality. Most manufacturers have continued to use aluminum for its mechanical and thermal resistance.
For larger immersion heaters for uses such as atomic power plants, heavier denser metals are required.

The dark blue section in the above image is the enclosure that contains the wiring for the pictured pipe insert,
indirect immersion heater.
Temperature Range:
The temperature range for immersion heaters is dependent on how it will be used. Most industrial heaters are
designed to heat water to around 900°F or 482°C. Depending on application requirements, the amount of heat will
remain constant. Two key factors in the amount of heat produced are the voltage supply and resistance.
Heating Element:

The heating element of an immersion heater is made of a combination of nickel and chrome, known as nichrome,
with refractory metals tungsten, molybdenum, or tantalum, encased in stainless steel or titanium. The majority of
heating elements are insulated with magnesium as a filler between the heating element and sheath.

The composition of heating elements can vary depending on the material to be heated. Low alloy steels are used
for heating elements that are designed to heat oil or gas. Below is an immersion heater with a stainless steel
heating element for the brewing process.
Insulation in immersion heater:
Insulation resistance is a key parameter for any electric heater to operate safely. All Watlow® heaters undergo
insulation resistance testing before leaving the manufacturing facilities. However, during shipping and storage,
the mineral insulation (magnesium oxide or MgO) material used in metal sheath heaters can absorb moisture
rendering the heater unusable until the moisture is purged from the heater.
Moisture impacts the functionality and performance of mineral insulated heaters and increases the likelihood of
a short-to-ground episode. Although all heaters should have their insulation resistance tested before installation,
heaters held in storage for long periods of time or used in high humidity regions are especially vulnerable to
absorbing moisture from the ambient environment and should, therefore, always be tested before use. When too
much moisture has been absorbed from the surrounding atmospheric humidity, the heater can become “wet” and
must be purged of all moisture prior to use.
An insulation resistance test, or megohm test, is required to determine the quality of the insulation within the
heating elements. This test is easy to perform and should be completed before putting any electric heater into
service. This critical step will help avoid the installation of a “wet heater” that will have a higher chance of causing
damage or shorting out.
Insulation Resistance:
For an electric heater to work correctly, current needs to flow directly through the coil wires within the heating
element and not be able to short to the outer sheath through the absorbed moisture. The greater a heater’s

284

CITS : E & H - Electronics Mechanic - Lesson 160 - 179