The use of 3-wire range and dryer receptacles has caused a lot of confusion and misapplication over the years. During World War 2 the War Materials Boards decided to allow TN-C ( Terra
Neutral Common ) grounding of cooking and clothes drying equipment in wood frame dwellings. TN-C grounding uses the
neutral as the equipment
ground as opposed to TN-S ( Terra
Neutral Separate ) for branch circuits and feeders which uses separate
neutral and equipment grounds.
Most electrical services in the U.S. are grounded TN-C-S with the
neutral as the equipment
ground as one and the same ahead of the service
switch and separate equipment grounds downstream of the service
switch. That TN-C was allowed downstream of a service during and after World War 2 has caused a lot of confusion.
A 4-wire range or dryer
receptacle is legal on a
stage provided that the plugs are field wired with extra hard usage ( no Js ) industrial
cord.
It could be worse. There is a colorblind electrician running around Cleveland, Ohio. What he did at International Exposition Center was to get hot and equipment
ground swapped on some 480 volt extension cords.
Mike Cole