A ballast which is fully potted can be installed inside an aquarium or
terrarium cover where it might be exposed to condensation. One which is
not completely potted poses a risk for electrical shock. After a recent
pipe break in my basement, I found that many of the electrical components
in a voltage regulating transformer had their terminals etched away.
Apparently, a film of moisture had wicked up over them and the metal was
electrolyzed away.
Also, a ballast which is fully metal enclosed and which uses high
temperature insulation can be mounted anywhere without fire hazard. One
which is not enclosed must be installed in a fireproof enclosure so that
a short does not result in the ballast igniting surrounding materials. A
metal enclosed ballast which does not use high-temperature insulation
must be provided with ventillation or it will cook itself, eventually
shorting out.
For both reasons, one must determine what kind of environment the ballast
was designed for before deciding how to mount it. This is true even for
integral solid-state ballasts. I have had more than one of the GE
screw-in fluorescents fail with bad solid-state ballasts. I no longer buy
that brand and suspect that the bulb leaks enough heat back into the
ballast to shorten its lifespan.
The packaging is often more expensive to manufacture than the internals
and due to its size and weight may be more expensive to ship. That and
achieving UL certification may drive the higher price that we pay here.
Bob Cruder - bcruder@miaco.com