apples and oranges.

the ( approx 1.2 cu ft ) metal space inside of a microwave oven is
a " resonant " tuned circuit .... designed to resonate the microwave
oscillator tube at it's designed operating freq. this tuned circuit
impacts the total current drawn by the tube ( out of resonance will
cause it to over heat ) ...... and promote power output into the load
placed inside the " e " field of the microwave oven . grounded or
not is not relevant ... except related to RF / emf interference
related to the microwave RF signal or the power supply.
spaces too large or too small would not work ... causing the tube
to self destruct at worse and at the least preventing too little power
to load ( flow ) into the space to cook anything. the microwave
tube doesn't care about grounding ... it's all about size
and shape to the tube.

RF proof faraday shielded rooms ...... like the ones that used to be
found in every hospital , back in the '50s , '60s and '70s ( tube
type ekg diagnostic heart monitor machines used to be particularly
susceptible to RF and EMF field interference ... this before the
advent of " balanced " , common mode , noise canceling circuitry.
( found in ALL modern EKG machines ) are most definitely grounded
to a earth ground where they are located. there used to be standards
that the copper room shield grid had to have less than 1/4 to 1/2 of
1 ohm resistance between each copper shield plate and between those
and ANY and every earth ground it was connected to. ( even the
doorway and door had to be metal and had wires connecting them to the
room walls ) these rooms are VERY RF proof and absolutely NO signals
get into them or out of them . not am radio , not FM radio , not VHF
handhelds and certainly not cellfones. the quality of the grounding ,
or said in another way , the lower the resistance between the
shielding and the earth ground ...
the more effective the shielded room works. EMF in particular ,
more than RF ..can penetrate the room more easily as the quality of
the ground of the copped shield diminishes. 20 to 50 ohms between the
shield and ground and you have a giant square , resonant RF antenna
that picks up everything.


these shielded rooms were necessary in the old days to insure the
proper function of the ekg and eeg equipment ... no longer a problem
with modern day circuit designs. these rooms have , for the most
part, been disassembled and the huge amount of copper sold off
for scrap.

resonant cavities of microwave ovens ( the inside cooking space ) and
faraday shielded rooms have practically NO technical commonality.

apples and oranges ....



k.....................


I am assuming that a microwave oven is a Faraday cage. Since it keeps
the radiation trapped, bouncing around inside to heat up the food
instead of you.