Life Factor # 2 (continued)
Heater Design
Last week we explored Heater Design and its impact on the working life of a cartridge heater.
Dielectric or insulation of the coil in the sheath and heat movement away from coil are both
significant factors. The two failure modes of any cartridge heater are a short to ground and
an opening of the electrical continuity. Therefore, the other major consideration in heater
design that impacts life is the integrity of the coil.
The gage or size of the wire is simply a matter of applying Ohms Law to the specification for
the heater. Watts and volts establish a resistance and the wire that is coiled has a specific
resistance per inch that provides total ohms required. There are a few design processes that
can be employed to optimize the winding to provide a more substantial wire, as very fine wire
will heat fatigue and open much more easily than a thick, larger diameter wire.
Very occasionally, we will contact you to ask if we can change the specification, possibly
halving the voltage and running heaters in series. This will result in a much more substantial
resistance coil and elimination of early failure from heat fatigue of fine wire. As always,
Dalton will be seeking to optimize the working life of the heater.