According to JimE :

I have read this thread with interest since I am facing a similar
situation. The wiring in my cement-walled older home was run inside the
walls when they were poured, making adding new wiring very difficult. I
have just remodeled a bedroom suite and replaced a pullman-style
one-piece stove/sink/fridge metal unit with new cabinets and a drop-in
cooktop, new frdge, etc. The problem is that there is only a 240v 3
wire outlet on that wall. This outlet is what powered the old unit,
which also had 120v outlets on it that were powered by this outlet. I
need a 120v outlet to power the new fridge and it appears that the only
reasonable option is to tap off one of the hot legs. All three outlet
wires are insulated and all the ground and neutral wires in my house
are attached to the same bus bar in the distribution panel. The outlet
is powered by a 30 amp breaker. While I understand that the codes exist
for a reason, I also know that most older homes do not meet current
codes. And don't most stoves and ovens have 120v loads supplied by
their 240v breaker? What exactly is the risk of my plan? There must be
some level of acceptable risk of non-compliance or most of the older
homes in the US would be uninhabital due to code non-compliance.

The main difficulties people encounter switching 240V outlets over
to 120V is that the result isn't breakered properly and/or has no
ground.

Or they try to mix 240V and 120V devices on the same circuit.
Yes, stoves and dryers are such, but they're single devices, not
multiple. There's a reason why stoves and dryers are supposed
to be the _only_ things on their circuits.

You say that you have a 240V 3 wire receptacle in the wall with
other 120V outlets attached to it. This is illegal for at least
three reasons:

1) The 120V outlets cannot have proper grounds. Ground != neutral,
potentially quite dangerous.
2) The 120V outlets are inherently breakered at 30A - highly
dangerous.
3) Mixture of different voltages for seperate devices.

The closest you can get to "right", without pulling new wire, is
to rearrange the wiring in the panel so that it's a single 120V
circuit on a 15A or 20A breaker (with oversize wire, but that's
okay). Which ends up needing to use an insulated wire as ground -
you have to use the white as neutral - so that means you'll have to
use a black or red as ground.

Code-wise that's illegal, but an inspector may permit it if you
have no other reasonable alternative.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.