NEC Nameplate Data - FLA or FLC?

[Phyzik]

When calculating the full load current for the nameplate on an industrial panel for motors do they mean the full load current as calculated from the look up tables or do they mean full load amperage from the nameplates? I get that they say full load current in the text of the code, but without a method of calculation I am not sure that is what they mean. FLC and FLA seem to get thrown around interchangeably in the code at times. The one thing that does make me think it should be the current from the tables is when you use nameplate they seem to specifically call it out. This is throwing me for a loop since my fellow engineers have always used FLA from the motor nameplate to figure the panel FLA for the panel nameplate. If I am going to shake the apple cart I feel like I need solid evidence and not just a grammar argument.

 

[Dennis Alwon]

Usually for most motors you would use the nameplate for overload calculation. For the rest see 430.6

430.6(A)(1) Table Values. Other than for motors built for low speeds
(less than 1200 RPM) or high torques, and for multispeed
motors, the values given in Table 430.247, Table 430.248,
Table 430.249, and Table 430.250 shall be used to determine
the ampacity of conductors or ampere ratings of switches,
branch-circuit short-circuit and ground-fault protection,
instead of the actual current rating marked on the motor
nameplate. Where a motor is marked in amperes, but not
horsepower, the horsepower rating shall be assumed to be that
corresponding to the value given in Table 430.247, Table
430.248, Table 430.249, and Table 430.250, interpolated if
necessary. Motors built for low speeds (less than 1200 RPM) or
high torques may have higher full-load currents, and multispeed
motors will have full-load current varying with speed, in
which case the nameplate current ratings shall be used.

There are exceptions

430.6(A)(2) Nameplate Values. Separate motor overload protection
shall be based on the motor nameplate current rating.

 

[don_resqcapt19]

When calculating the full load current for the nameplate on an industrial panel for motors do they mean the full load current as calculated from the look up tables or do they mean full load amperage from the nameplates? I get that they say full load current in the text of the code, but without a method of calculation I am not sure that is what they mean. FLC and FLA seem to get thrown around interchangeably in the code at times. The one thing that does make me think it should be the current from the tables is when you use nameplate they seem to specifically call it out. This is throwing me for a loop since my fellow engineers have always used FLA from the motor nameplate to figure the panel FLA for the panel nameplate. If I am going to shake the apple cart I feel like I need solid evidence and not just a grammar argument.

As far as I know there is no place in Article 430 that uses FLA. There is nameplate FLC and code FLC that are used in the NEC.

 

[Phyzik]

Usually for most motors you would use the nameplate for overload calculation. For the rest see 430.6



There are exceptions

So basically unless it says to use the nameplate in the code I use the lookup tables.

 

[texie]

So basically unless it says to use the nameplate in the code I use the lookup tables.

I would say yes as 430 requires all the branch circuit elements to be based on table values with the exception of OL which uses nameplate.

 

[Carultch]

So basically unless it says to use the nameplate in the code I use the lookup tables.

Correct.

One way to help understand why this is the case, is that the FLC is a representative value of the current for that particular mechanical power rating of motor, that is generally a conservative value compared to most FLA values of available motors. In the event that the motor is replaced with an equivalent motor of the same horsepower, you'd still have a sufficient circuit for it.

FLA by contrast, is product-specific. While these aren't the real meanings of the letters, think of FLC as "full load code", and FLA as "full load actual".

 

[don_resqcapt19]

Correct.

One way to help understand why this is the case, is that the FLC is a representative value of the current for that particular mechanical power rating of motor, that is generally a conservative value compared to most FLA values of available motors. In the event that the motor is replaced with an equivalent motor of the same horsepower, you'd still have a sufficient circuit for it.

FLA by contrast, is product-specific. While these aren't the real meanings of the letters, think of FLC as "full load code", and FLA as "full load actual".

Since the code never uses FLA in Article 430, I prefer FLC (code), and FLC (nameplate).

 

[inquisitive]

Just so I completely understand: the motor code FLC values, and not the motor nameplate FLC values, are used to calculate the FLC for a panel nameplate or industrial machine nameplate? If so, when motor info is listed on an electrical schematic, does this also need to be the code FLC values?

 

[don_resqcapt19]

Just so I completely understand: the motor code FLC values, and not the motor nameplate FLC values, are used to calculate the FLC for a panel nameplate or industrial machine nameplate? If so, when motor info is listed on an electrical schematic, does this also need to be the code FLC values?

When I put it on a schematic, it is always for the purposes of making sure the correct overloads are installed, so I use the nameplate current. The code does not care what you put on the schematic.