Allen-Bradley 1756-IA32 - Determine Max Motor Starters Example

236 Rockwell Automation Publication 1756-UM058G-EN-P - November 2012
Appendix E Motor Starters for Digital I/O Modules
Determine the Maximum Number of Motor Starters
To determine the maximum number of motor starters that can be used by any
1756 digital I/O module, refer to this example.
Table 64 - Number of Motor Starters to be Used
Step Value used in this example
1. Choose your motor starter. Allen-Bradley Bulletin 500 Size 3 120V AC/60 Hz/2-3 Poles. Inrush 1225VA, Sealed=45VA
2. Determine the number of motor starters required for your
application.
12 size 3 motor starters
3. Choose a ControlLogix digital output module. 1756-OA16I
• Output voltage = 74…265V AC
• Output steady state current per point = 2A maximum @ 30 °C (86 °F)
• & 1A maximum @ 60 °C (140 °F) Linear derating
• Output steady state current per module = 5A maximum @ 30 °C (86 °F) & 4A maximum @ 60xC (linear derating)
• Output surge current p= 20A maximum for 43 ms repeatable every 2 s @ 60 °C (140 °F)
4. Determine the maximum environmental operating
temperature.
50 °C (122 °F)
5. Confirm the voltage range is within the motor starter
range.
Motor starter uses 120V AC
1756-OA16I operates in a 74…120V AC voltage range
6. Confirm the inrush current per point. Inrush of motor starter - Line voltage = Inrush current = 1225VA/120V AC = 10.2 A Inrush
7. Confirm the steady state point current of the module can
drive the motor starter.
Sealed/Line voltage = Steady state current = 45VA/120V AC = 0.375 A @ 50 °C (122 °F)
Output point current can drive: 2 A - (.033 mA x 10 °C) = 2 A - 0.33 A = 1.67 A @ 50 °C (122 °F)
Above 30 °C (86 °F), output point derates to .033 mA/°C (point derating)
The 1756-OA16I output point current (1.67A) can drive the motor starter (0.375 A @ 50 °C (122 °F)
8. Confirm the 1756-OA16I/A total module current can drive
12 size 3 motor starters @ 50 °C (122 °F).
Motor starter steady state current x 11 motor starters = .375 x 12 = 4.5A @ 50 °C (122 °F)
The output total module current can drive: 5A - (.033 mA x 10 x C) = 5A -0.33 A =4.67 A @ 50 °C (122 °F)
Above 30 °C (86 °F) total output current derates to .033 mA/x C (Module derating)
The 1756-OA16I total output current (4.67A) can drive the 12 motor starters (4.5 A) @ 50 °C (122 °F)