What is the maximum distance of RS 485?

Answer 1

It depends on the wires' diameter you use, and the network topology you will use. Generally say the bigger the diameter you use, the distance longer. But it is the best you use it in BUS of hand in hand. If you use RS485 in tree or star network, it can not be long because of the signal's reflex on lines. What i said above must be twisted-pair, otherwise the distance can not by far. Also you need to consider the data rate you use. the lower data rate you use the longer distance you will get. But all above i said, even in the best condition, RS485 is only 300~500 meters long. If longer distance you need, you have to consider other way, such as RS485 module which use other technology to expand the distance, just only RS485 interface but not RS485 signal on the lines. For example, the PWBS01H series module i used before. It makes RS485 be 3000m distance, also supports tree or start network topology. here is the link for PWBS01H series module.
slideshare.net/eddiegao/bestrong-rs485-powerbusmodules

Answer 2

It depends on the wires' diameter you use, and the network topology you will use. Generally say the bigger the diameter you use, the distance longer. But it is the best you use it in BUS of hand in hand. If you use RS485 in tree or star network, it can not be long because of the signal's reflex on lines. What i said above must be twisted-pair, otherwise the distance can not by far. Also you need to consider the data rate you use. the lower data rate you use the longer distance you will get. But all above i said, even in the best condition, RS485 is only 300~500 meters long. If longer distance you need, you have to consider other way, such as RS485 module which use other technology to expand the distance, just only RS485 interface but not RS485 signal on the lines. For example, the PWBS01H series module i used before. It makes RS485 be 3000m distance, also supports tree or start network topology. here is the link for PWBS01H series module.

slideshare.net/eddiegao/bestrong-rs485-powerbusmodules