Hello RAMY 1,

Check this out, my office is about 4km away from the nearest local telephone exhange and we have a 200 pair 0.6mm diameter jelly filled steel amoured pe insullated telephone cable run between the local exchange and my office mdf; approximately 4000m.

Again, my friends office is 6km from the exchange and has something similar. To this day everything is working fine.

Furthermore, we have a PABX which has some extension users 1km from the the PABX.

To be precise, the maximum length is determined by the output voltage of the source exchange (PABX or PSTN local exchange)

Cheers,

ethobil