Transformer wiring

I have a 24vdc 10amp single secondary transformer for my PS. The
pimary has 2 black #20 wires and the secondary has 3 #14 wires. the
two outer wires are solid green and the center wire is green with a
yellow stripe. How are the 3 secondary wires hooked up to the bridge
rectifier and why is the secondary wire size larger than the primary?

Thanks

Jay