The Model Railway Club's OO test tracks were originally fitted with the inner circuit with switchable stud contact, the middle circuit with switchable outside third , and the outer circuit EM with stud contact!
I've never seen the outside third being used by anybody at the club in the 1960s, the stud contact would sometimes run Hornby double 3-rail, alert rather erattically. The test tracks were rebuilt by myself, Grovenor of this parish, and others to OO, OO with N, and P4/OO, dispensing with third rail and stud contact.