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Discussion Starter · #1 ·
Greetings,

Question about the CEC regarding VFD's.

Im doing a sand blasting project. I have the following loads

.77A 120Vac single phase gear motor, controlled across the line.
.7A dc motor controlled by a 120Vac KB penta DC drive
100W powersupply for PLC,PLC in/out modules, and 3 input inductive sensors.
x1 120Vac solenoid valve
x3 120Vac contactors

My question is how do i correctly size the feeder conductor to supply my cabinet containing all these electronic/electrical components. The feeder will be connected to a disconnect inside the machine.

Feeder demand Calc.
1. From my current understanding. I take the FLA of largest motor x125% (section 28-108)
2. Then do i take the FLA of the smaller motor which is controlled by the VFD or do i take the wattage input rating of VFD? (which do i add the VFD input power or the motor FLA which is controlled by the VFD.)
3. then ill take the wattage of my power supply and other connected loads (solenoid and contactor coil wattage) and add this to my feeder calc at 100%.

can somebody please clarify whether i add the VFD rating or motor rating towards feeder.
Thanks and bare with me.
 

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IBEW L.U. 1852
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5,261 Posts
Section 28 of the CEC has never really been too clear on the installation of feeders for VFD's....at least to me anyway. I know that most of the engineers that I do work for size the feeder according to the motor's FLA not the capacity of the VFD.
For what you are describing in your project....I wouldn't get overly concerned about it. The loads you are describing are small and I think you're feeders will be able to handle the load no matter which way you go.
 

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Discussion Starter · #3 ·
Ok thank you, and yes your right the loads i am dealing with now are tiny. I just figured i better get some insight because this project is a stepping stone towards future projects that i will be dealing with and designing. they will require larger loads and will be inspected so i thought i better learn now before mistakes are costly :)
 

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IBEW L.U. 1852
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5,261 Posts
Good idea.....just to be 100% certain, before you go too far on the larger projects, clarify the question with your local inspector before you do the job. Never hurts.
 
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