I am a residential elec. contractor studying for my commercial lic. and I would like to know.....When you have several motors(3 phase)1 intermitten, 1 5 min rated, 1, 15 min rated and 2 continuous how do figure the load calc.? I really need specifics and %. Is it the highest rated fLCx 125% + sum of flc of all the other motors or do multiply from table 430.22(e)first then add that number?
Motor calculations
- Thread starter Brandymg
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brantmacga
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conductor load calc is 430.24 - if you have the type of motor specified in 430.22(E) then you calculate that single motor load according to the table provided. then you add that current total to those of the other motors connected and calculate using 430.24.
Here you go
Here you go
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Step 1. F.L.C (full load current) T 430.248 -1 phase-T430.250 3 phase.
Step 2. Motor running overload protection or heaters 430.32a1 min,430.32c max.(Use motor name plate only for heaters if given)
Step 3.Branch Circuit Wire Size.430.22 FLCx125%=required ampacity
Table 310.16 size wire ampacity to insulation.
Step 4. Branch circiut over current protection(fuse or cb) shall be selected from table 430.52.First select the type of motor (1 phase or 3 phase AC or DC wound rotor,code letter) next select type of protection(non-time delay,dual element,inverse time CB) now select the percentage from the propper colunm and multiply it times the FLC of the motor.Use 240.6 to select the standard size,code permits the next size up per 430.52 ex. 1
Step 5 Feeder conductor size 430.24. Multiply the largest rated motor in FLC by 125% and add the FLC of all the other motors connected to the (SAME feeder) conductor for required ampacity T 310.16.
Step 6 Feeder over current protection 430.62.Select the largest branch circuit (over current device) and add all the other motor FLC connected on the (SAME feeder) to select feeder fuse or .Code does not permit going up must go down . (Remember on three phase motors draw it out on paper,only count the lines attached to the phases Dont count all the motors)
Here you go
--------------------------------------------------------------------------------Step 1. F.L.C (full load current) T 430.248 -1 phase-T430.250 3 phase.
Step 2. Motor running overload protection or heaters 430.32a1 min,430.32c max.(Use motor name plate only for heaters if given)
Step 3.Branch Circuit Wire Size.430.22 FLCx125%=required ampacity
Table 310.16 size wire ampacity to insulation.
Step 4. Branch circiut over current protection(fuse or cb) shall be selected from table 430.52.First select the type of motor (1 phase or 3 phase AC or DC wound rotor,code letter) next select type of protection(non-time delay,dual element,inverse time CB) now select the percentage from the propper colunm and multiply it times the FLC of the motor.Use 240.6 to select the standard size,code permits the next size up per 430.52 ex. 1
Step 5 Feeder conductor size 430.24. Multiply the largest rated motor in FLC by 125% and add the FLC of all the other motors connected to the (SAME feeder) conductor for required ampacity T 310.16.
Step 6 Feeder over current protection 430.62.Select the largest branch circuit (over current device) and add all the other motor FLC connected on the (SAME feeder) to select feeder fuse or .Code does not permit going up must go down . (Remember on three phase motors draw it out on paper,only count the lines attached to the phases Dont count all the motors)
Here is a site that migth help also http://www.ecmag.com/index.cfm?fa=article&articleID=4091
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