According to Tom Horne :

Generally an excellent post, but I think this bears commenting on:

In the older three wire configuration any failure of the neutral
conductor energizes the frame to the potential of the circuit. In the
four wire configuration the neutral opening causes the appliance to stop
functioning but the frame will remain at zero volts relative to other
grounded surfaces.

The problem with 240V/120V appliances is that if you lose the neutral,
the appliance doesn't necessarily "completely" stop working. Regardless
of whether it's 3 or 4 wire attached.

For example, with most stoves, if you lose the neutral, the only likely
symptom is that the clock stops working (but it won't necessarily![*]),
yet, the cooktop and oven continue working. Because they don't use the
neutral.[+]

Similarly, with a dryer, the heating elements will continue to work,
but the drum and blower will stop operating.

With a stove, you may not even notice that this has happened - the stove
still cooks dinner. With a dryer, if you're not there to notice (or, you
think it finished it's cycle), you won't notice.

In and of itself, losing the neutral for a stove is harmless. With a
dryer, you may well end up having to rely on the thermal cutout preventing
a house fire.

Furthermore, if the stove or dryer is on a three wire connection, the frame
now becomes directly part of the circuit - if you touch a better ground
(like a faucet), you can get zapped by the unbalanced current flowing thru
the clock (or drum rotator motor or timer motor on a dryer).

At least with four wire, you have a vastly better chance of the frame _not_
becoming part of the circuit and you won't get zapped by the clock.
[*] the clock may continue to function but _only_ during the times that
the elements are powered up. On a dryer, the timer/motor may "work" (possibly
very badly or not at all with black smoke) when the elements are powered up.
Depends on where the break is.

[+] I encountered a similar situation. In reverse. I helped rewire a
friend's house. They had to live in the place during renovations, so,
there was always being work done. Got a call several days after I
installed (and tested) a new 4-wire stove circuit with the complaint
that "the clock's working, but nothing else is". After much
head-scratching, I managed to figure out that my friend had removed and
reinstalled the duplex breaker for the stove (because he was adding
something else). This particular panel (a FPE) alternated legs in _pairs_
(AABBAABB) not individually (ABABAB) and he had reinstalled the breaker
such that both breakers were on the same leg. _Both_ ends of the heating
elements were attached to the same leg, so the elements didn't work. But
the clock was quite happy.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.