Electrical Dryer outlet
This meant that @ 240volts there was Hot-Hot-Ground.
The problem was that ranges and dryers began evolving many 120vac assessories, lights, timers, bells, whistles , etc....
This meant current was 'returning' on the grounding conductor. Granted, a negligible qantity at first, but increasingly so, thus this introducing a hazard.
So it became a code ( i'm thinking the 93' or 96' cycle without looking) to have a 4-prong receptacle and 'pigtail'
( cord from unit).
so now we have Hot-Hot-Nuetral-Ground
This is not so far fetched if one considers the modern day receptacle that has Hot-Nuetral-Ground ( looks like a face with the ground down)
There is a real hazard with the Three (3) conductor cord-sets by using the Neutral for both the neutral and the equipment grounding conducor. Especially since the motor is 120 volts, if by chance you lose the neutral, albeit loose, broken or if it comes apart, the whole appliance will be energised and can become a serious shock hazard.
Be careful and be safe.