What are these called ?

Some type of transformer at the main entry (black round things with 200 writing on sides). What is the name of this and what do they do ? Thank s

Beidleman-Millbrook 252.JPG

Beidleman-Millbrook 252.JPG

Beidleman-Millbrook 252.JPG

Beidleman-Millbrook 253.JPG

Current transformers more info to follow .
Usually use for large amperage services .

http://www.electricityforum.com/electrical-transformers/current-transformer-basics.html

http://en.wikipedia.org/wiki/Current_transformer

The 200 is the ratio typically to 5 so those would be a 200 to 5 ratio CT. 200 amps through the CT will provide 5 amps of output to be measured by the metering equipment.

Thank You…Roy