As has been mentioned screened should not be required. in theory on rs485 on the correct UTP cable.

But while there sometimes can be issues with screened (ie increased cap etc) it usually causes softer square waves or slow slopes.

But noise can also be an issue etc.

In theory a cat5 would be ideal with all spare cores grounded. However id still use a screened beldon any day over cat 5.

Agreed

If problems on any cable, grounding spare cores will allways help (only one end though same with screen core), I do that on any install if I have the time. (the spares, screen always)

Aparrently the only type of alarm twisted cable would not be good for is ID circuits.

I think I read this somewhere screened is fine but twisted nope (ID only)

best info http://www.maxim-ic.com/appnotes.cfm/an_pk/763/

Edited April 20, 200917 yr by y-i-out-of-bed