A Very Strange and Unusual Breaker and Electrical Service which where banned but may still be out there in rural areas. the Delta Breaker

 Now after 40 plus years in the field and seeing almost every type of power  service configuration   from 480- 3 phase Delta to 230 Volt 2Phase and 240- High leg 3Phase  I recently ran across an article a fellow long time electrician shared .

Its Called a Delta breaker and they where banned in 1973 .

 A delta breaker is a load center breaker with 2 plug in stabs and a third wire from the third terminal that goes to the third leg of a transformer. This allowed you to use a single phase load center and get three phase power by running a third wire back to the transformer.

 This breaker was designed so a  standard 3 wire electrical service breaker panel could be used 

instead of having to purchase a more expensive 3 phase panel .

You would find them in old mom& pop general stores where their was 1 -3 phase load 

like a Cooler.  as everything else used single phase 230 or 120 volts.

Personally I have never seen one and have done plenty of work in rural America. 

Many power company's paid for or made customers switch to the more expensive 3 phase  4 panels where all 3 hot wires are clearly marked and visible. 

But these types of services could well be still out their in the backwoods some where and if you work in those areas you should be aware of them.