Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 240)

Publication 1757-UM006A-EN-P - May 2002
D-4 Fieldbus Wiring Considerations
The following table lists limits for some possible fieldbus cable types
listed in the order of usage preference with 1 being preferred.
Another rule of thumb based on Fieldbus Foundation published
guidelines is for the length of spurs and how many devices can be on
various lengths of cable as listed in the following table.
Table D.2 Fieldbus Cable Limits
Preference
Type Description Distance
(Meters/Feet) Resistance
(Ohms per km) Attenuation
(dB per km)
1 #18 AWG, shielded,
twisted pair 1900/6233 22 3
2 #22 AWG,
multiple-twisted,
pairs with overall
shield 1200/3937 56 5
3 #26 AWG,
multiple-twisted,
pairs without shield 400/1312 132 8
4 #16 AWG, multiple
conductor, no
twisted pairs with
overall shield 200/656 20 8
Table D.3 Number of devices on the fieldbus and maximum spur length
Number of Devices Maximum Spur Length (Meter/Feet)
1 to 12 120/394 (one device per Spur)
13 to 14 90/295 (one device per Spur)
15 to 18 60/197 (one device per Spur)
19 to 24 30/98 (one device per Spur)
25 to 32 No spurs allowed
ATTENTION
!
The spur length limitations are for spurs with one
device each. Please refer to the Fieldbus Foundation
AG-140 Wiring and Installation Guide for rules on
multiple devices per spur.