Rockwell Automation DeviceNet Media Design Installation Guide - Manual (Page 98)

Publication DNET-UM072C-EN-P - July 2004
4-20 Determine Power Requirements
9. Find the value next largest to the length of section 2 using Figure 4.3 on
page 4-6 to determine the approximate maximum current allowed.
280m (7.69A)
Since the total current does not exceed the maximum allowable current,
section 2 will operate properly (3.50A
≤ 7.69A).
Loading is 46% (3.50/7.69).
If the middle section is still overloaded after you move the power supplies
closer together, add a third power supply. Then recalculate each segment.
Use the Full-calculation
Method Use the full-calculation method if your initial evaluation indicates that one
section is overloaded or if the requirements of your configuration cannot be
met by using the look-up method.
IMPORTANT
If the total current in the section exceeds the maximum
current, move the power supplies closer together and
repeat steps 7-9 until the total current in the section is less
than the maximum allowable current.
IMPORTANT
Section 1 + Section 2 + Section 3 = 7.3A. This is > 4A and
does not comply with the NEC/CECode for Class 2
installations.
IMPORTANT
To determine spare capacity for future expansion,
subtract the actual current from the maximum allowable
current. To determine the percentage loading for each
segment, divide the maximum allowable current into the
actual curren
t.
Segment Maximum Current -
Actual Current = Spare Capacity % Loading/Segment
1 2.85A - 2.25A= 0.60A 79% (2.25A/2.85A)
2 3.83A - 3.50A= 0.33A 91% (3.50A/3.83A)
3 1.70A - 1.55A= 0.15A 91% (1.55A/1.70A)
Results
IMPORTANT
Before constructing the cable system, repeat all calculations
to avoid errors.