Are you sure it didn’t have a normal plug, with a separate clip for a reliable chassis ground? I don’t see how the half plug with a neutral wire to a radiator w

Are you sure it didn’t have a normal plug, with a separate clip for a reliable chassis ground? I don’t see how the half plug with a neutral wire to a radiator would be “safe”, even when compared to a neutral-connected chassis with an unpolarized plug. “The hot side is accessible to the user” is still true, just remove the wire to the radiator, now it‘s at line potential.