Typical telephone line DC voltage is 48V and ring voltage is typically 90 vrms or 130V peak but can be upt to 130V RMS.
Calculations would be rather difficult as the line is a physical thing..
Regards,
IanP
could you tell me the highest votage on T1 line and ISDN line? I have to select a lightning protection component baseing on this. Thanks for your any help.
" .Recommendation: Any over-voltage protectors (Gas Arrestors or similar) which are connected to the earth bonding of the product shall have a minimum DC sparkover voltage of 1.6 times the rated voltage of the unit."
For more see "Telecom Design Guide" : **broken link removed**