Motor FLA Tables
Motor FLA Tables
(OP)
Table 44 of CEC 2006 Part I and the NEC Motor FLA Table are similar and they indicate Full Load Amps for various HP and voltage ratings. Note 4 of these tables indicates that for 90% and 80% power factor, 1.1 and 1.25 are to be multiplied to the FLA values in the tables. My question is, at what %PF BASE or %EFFICIENCY BASE are the values on the table derived from. I am trying to create a typical motor FLA database and hoping to derive them from Code tables as part of my conductor sizing calculations...Any comments?
I would appreciate if somebody could share me a typical FLA table for various voltages which I can conservatively use aside from the Code tables as an option. Thanks
I would appreciate if somebody could share me a typical FLA table for various voltages which I can conservatively use aside from the Code tables as an option. Thanks





RE: Motor FLA Tables
This would be for a synchronous motor rated for use at a power factor other than unity to supply VARs to the system.
That is, a motor may be rated at 500 HP, unity PF, or rated at 400 HP, 0.8 PF. (Or the 500 HP motor may be used at 0.8 PF provided that the mechanical load does not exceed 400 HP.
Note, in the CEC this table is a guide, and the motor nameplate data is used for conductor sizing.
In the NEC, the table is used rather than the motor nameplate.
Bill
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"Why not the best?"
Jimmy Carter
RE: Motor FLA Tables
The power factor calculated will also going to be used for the voltage drop calculation which is:
Vdrop = 1.732 x FLA x L x (RcosY + XsinY) where Y = angle
I just noticed using the published client efficiencies and CEC FLAs, I am getting low power factor values as low as 78% for a 60HP at an efficiency of 92.4% to get a CEC FLA of 77A @ 460VAC.
RE: Motor FLA Tables
http:
(see section 1.9)
The motor application is mostly Class 1, Div 2, NEMA Design B and TEFC.
Any further comments and suggestions are higly appreciated.
RE: Motor FLA Tables
Usually the OEM selects typical motor brands (non VFD, and VFD rated) , motor brand manufacturer gives up the lists giving FLA eff and HP. Use this lists for the FLAs, eff, and hp.
If customer requests different, mechanical will usually pass this info during turnover.
we usually have two or three different lists of FLA motor brands.
I do not start on a project until mechanical is done
Why would you worry about PF in calculating wire sizes?
RE: Motor FLA Tables
By using typical current values, you avoid the possibility of a high efficiency motor being replaced with a low efficiency motor on conductors that may be undersized.
I would suggest looking at some motor catalogs and picking a current value for each size of motor that is in the upper part of the current range. In many instances the wire size won't change and you will have adequate capacity in the event that a motor is changed at a later date and the only motor available has a lower efficiency than the original design motor.
Bill
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"Why not the best?"
Jimmy Carter
RE: Motor FLA Tables
With today's high efficiency and especially the premium efficiency motors, actual FLA's are a bit and sometimes more than a bit lower than the NEC amps for the same motor.
RE: Motor FLA Tables
So in NEC land, sizing motor conductors is generally cut and dried.
RE: Motor FLA Tables
There are only two alternatives, either use Code tables or use acual value on the nameplate. Anything else is conjecture and waste of time. Plus using anything less than what Code suggests would only be a liability as dpc pointed out.
RE: Motor FLA Tables
RE: Motor FLA Tables
If you are trying to compute motor kW, kVA, etc, then I would use typical data from two or three manufacturers and take a worst case or an average.
RE: Motor FLA Tables
I will revise my calculation and provide notes of the basis of the FLA and other motor parameters. For ampacity check, the Code FLA values will be in use.
Now, going to the voltage drop. If I have both resistance and reactance values for the conductors in ohms per 1000', the the motor operating power factor is required and in this case I will assume 80%. However, I also see Table 44 of the CEC code note 4 (which might be a similar note in the NEC)indicates that a multiplying factor of 1.1 and 1.25 will be used on the code table FLAs for 90% and 80% power factor respectively, hence a 10HP motor at 460VAC with a Code FLA of 14A should be 17.5A for a power factor of 80%. If I am going to assume PF=80% for my Vdrop calculation, then I ahve to use 17.5A as FLA. Is this going to be way over-rated?
RE: Motor FLA Tables
Note 4 applies to synchronous motors only. 60 HP seems small for a synchronous motor.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Motor FLA Tables
I will use the code FLA for my induction machines regardless of power factor and efficiency. For the Vdrop calculation, I will assume a conservative PF=80%.
Thank you very much for all the supports and comments.