Electromagnetic coils in one form or another are used as solenoids for
the gas valve for your clothes dryer or your furnace to the low voltage
transformer for your air conditioner or fluorescent light fixture.
Recently these electromagnetic coils have been failing more frequently
due to either none or very little quality control in the countries in
which they are manufactured. To save money on copper these coils are
manufactured very close to their threshold of failure. Design
specifications require most of these coils to stay on continuously or
at least for very long periods and still remain relatively cool or at
least NOT hot to the touch. An electromagnetic coil basically consists
of a copper conductor (wire) covered with a high electrical insulation
varnish formulation. This copper wire is wound like a reel or spool
forming the coil. Ideally the length of the copper conductor should be
long enough to achieve its purpose plus a little to spare. This keeps
the coil from overheating and from reaching something called "core
saturation" which is basically the maximum capacity of current it can
handle. When enough copper is used the coil isn't anywhere near
saturation - and thus runs relatively cool, it will last essentially
forever. On the other hand when there ISN'T enough copper conductor
used ,"core saturation" is reached causing a build-up of high
temperature which eventually in time causes the insulation varnish
formulation to break down gradually increasing the current leakage and
even arching and humidity absorption. This leads to decrease of
resistance across the coil terminals, reduction of capacity and
eventual failure or burn out. In such a coil that is manufactured to
just barely meet specifications, even a small reduction of capacity may
be enough to cause it to fail to accomplish the purpose it was intended
for. An electronic coil that is hot to the touch IS NOT a normal
condition. It WILL fail prematurely. Either return the unit to the
manufacturer or be ready to replace it soon.