Interpreting UK Power networks dig plans

[tvrulesme]

Obtained a safe dig plan from uk power networks. Very annoyingly they don't include a key. Does anyone know where I can get hold of one?

 

Specifically interesting in

• what the green and red lines are
• the diamond shapes
• NR
• .15a +sl

 

Also, is it possible to find out for a given substation any info on the earthing system etc?

 

Thanks in advance