When can you use nameplate FLA?

cppoly

Senior Member
Location
New York
If a motor operated appliance lists FLA, you're allowed to use this current and you're not required to get the FLC from the NEC tables right?

So by extension, when a motor or motor appliance only lists HP, then you must use the tables??
 

paulengr

Senior Member
You use FLA for overload sizing. FLC for everything else under 430.

But shat you are describing sounds more like a 440 application which uses totally different rules from normal motors. You use what’s on the name plate. Are you sure you are in the right section?


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Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
This may be helpful

) General Motor Applications. For general motor applications,
current ratings shall be determined based on (A)(1) and
(A)(2).
(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
 

Besoeker3

Senior Member
Location
UK
If a motor operated appliance lists FLA, you're allowed to use this current and you're not required to get the FLC from the NEC tables right?

So by extension, when a motor or motor appliance only lists HP, then you must use the tables??
HP and nameplate FLA are two different things. FLA is input current. HP is output power. Tells you nothing about power factor or efficiency so you can't accurately determine FLA from that.
 

romex jockey

Senior Member
Location
Vermont
Example D8 Motor Circuit Conductors, Overload
Protection, and Short-Circuit and Ground-Fault
Protection uses 'nameplate FLC'

Unfortunately ,many motors one places a probe on won't portray this value until placed under a full load.

~RJ~
 

Besoeker3

Senior Member
Location
UK
You use FLA for overload sizing. FLC for everything else under 430.

But what you are describing sounds more like a 440 application which uses totally different rules from normal motors.
Ignorant Brit strikes again. Two questions this time.

What is the difference between FLA and FLC?
Full load Amps and full load current?
We'd usually use FLC as the abbreviation.

Second question.
By 440 application I assume you mean 440V ? Apart from that not being one of your standard voltages, in what way does it differ from what you consider to be a "normal" motor that requires totally different rules?
 

cppoly

Senior Member
Location
New York
Thanks for replies. I guess what I'm unsure about is when you can just look at the motor/motor appliance data sheet and use the FLA listed here and NOT be required to go to the NEC tables.

For example,

- If I have a motor operated appliance such as a blender, I would use the FLA listed on the appliance to determine the conductors and OCPD, right?

- What if I have a sump pump and control panel and the data sheet only lists Full Load Amps but doesn't give the horsepower. I would also use the full load amps right and not NEC tables?

Sometimes data sheets just don't give you HP so then you can use the FLA??
 

retirede

Senior Member
Location
Illinois
Ignorant Brit strikes again. Two questions this time.

What is the difference between FLA and FLC?
Full load Amps and full load current?
We'd usually use FLC as the abbreviation.

Second question.
By 440 application I assume you mean 440V ? Apart from that not being one of your standard voltages, in what way does it differ from what you consider to be a "normal" motor that requires totally different rules?
FLA and FLC are the same thing. I find FLA more commonly used over here.

“440” application refers to NEC article 440 - Air conditioning and refrigeration equipment.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
FLA and FLC are the same thing. I find FLA more commonly used over here. ...
No. That is incorrect. Commonly done, but commonly incorrect.

FLA is the marking on the motor nameplate by the motor manufacturer for the motor's Full Load Amps.

FLC (Full Load Current) is a current value from a table in the NEC (430.247 through 250 depending on source) that is assigned to each HP rating. You are REQUIRED by code to use the FLC values from the table, NOT the FLA from the motor, for sizing conductors, switching devices and short circuit protective devices. The reason is that someone may someday change the motor and it may have a different FLA on the nameplate, but if you sized everything via the chart, the numbers they used are conservative enough to make it (relatively) safe to do so.

The ONLY thing that you use FLA for is in selecting running Over Load protection, a.k.a. heaters or settings on adjustable OL relays, VFDs, soft starters etc..
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
If a motor operated appliance lists FLA, you're allowed to use this current and you're not required to get the FLC from the NEC tables right?

So by extension, when a motor or motor appliance only lists HP, then you must use the tables??
The current is motor-specific, so overload protection needs to be sized for that.

The horsepower is application-specific, so replacements must be accommodated.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
No. That is incorrect. Commonly done, but commonly incorrect.

FLA is the marking on the motor nameplate by the motor manufacturer for the motor's Full Load Amps.

FLC (Full Load Current) is a current value from a table in the NEC (430.247 through 250 depending on source) that is assigned to each HP rating. You are REQUIRED by code to use the FLC values from the table, NOT the FLA from the motor, for sizing conductors, switching devices and short circuit protective devices. The reason is that someone may someday change the motor and it may have a different FLA on the nameplate, but if you sized everything via the chart, the numbers they used are conservative enough to make it (relatively) safe to do so.

The ONLY thing that you use FLA for is in selecting running Over Load protection, a.k.a. heaters or settings on adjustable OL relays, VFDs, soft starters etc..
There is nothing in the NEC that says that, in fact the language from 430.32 says:
...motor nameplate full-load current rating ..
.
It has often been taught that way, but the code language never uses the term FLA. I teach nameplate current and Table or NEC current when I teach motors.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
There is nothing in the NEC that says that, in fact the language from 430.32 says:
...motor nameplate full-load current rating ..
OK, I see what you mean. You're right, it never says FLA vs FLC. It is explicit as to the difference between using the nameplate and using the charts, but it doesn't actually say FLA (or the words) anywhere. I stand corrected, I guess that was something I was taught in order to help avoid that confusion.

But maybe this is why... since you will never see the term FLA anywhere OTHER than on the motor nameplate, that's a good way to keep it straight. In fact NEMA MG 1 gives a definition of FLA as meaning "Full Load Amperes", and requires that "Amps" be shown on the nameplate, but it does NOT provide a definition of "FLC" nor use the word "current" in the nameplate requirements.

Semantics though.
 
Last edited:

paulengr

Senior Member
There is nothing in the NEC that says that, in fact the language from 430.32 says:


OK, I see what you mean. You're right, it never says FLA vs FLC. It is explicit as to the difference between using the nameplate and using the charts, but it doesn't actually say FLA (or the words) anywhere. I stand corrected, I guess that was something I was taught in order to help avoid that confusion.
That’s what I was taught. And yes 440 is for HVAC which includes compressors and equipment that includes motors where the sizing rules are a bit different. I might have to actually visit Europe some day to be called an ignorant Brit. Guess dumb southern redneck will have to do. I learned 440 in the Code not on the wall socket. Under that section there is no table...you use name plate.

I’m going to look closer though because at least on the exam for 9 states they use FLC and FLA as you describe them. I know there are some trick answers where using name plate gives you the wrong answer. JC Rodriguez writes the tests for 8 states and he doex it that way. He doesn’t write NC exams but they do it that way.

And I agree with your logic especially because I work for a motor shop. FLA changes a little even when we rewind.

Not 100% sure but I think the table values are based on converting HP to kw then applying a 0.85 power factor and using the ANSI standard utilization voltage so for instance 460 then calculating amos. That should be pretty close to worst case on just about any motor except maybe some strange ones like NEMA curve D.


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retirede

Senior Member
Location
Illinois
I guess I would say it this way:
From a technical perspective, FLA and FLC are the same (motor current in amps at full load), but conventions have evolved where the context of use implies a different source of the data.

??!
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
From a grammar standpoint, it would also depend on the nature of a question as asked.

Q: “What is the Full Load Current of that motor?
A: “123 Amps

Q: “What is the Full Load Amps of that motor?
A: “123

In the second version it would be redundant to respond “123 amps” because amps was already embedded in the question. But I can’t think of a way to word that question to where the proper response would be “123 Full Load Current
 

cppoly

Senior Member
Location
New York
I should have given this reference originally:

430.6 Ampacity and Motor Rating Determination.
(A) General Motor Applications. For general motor applications, current ratings shall be determined based on (A)(1) and (A)(2).
(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.


Exception No. 3: For a listed motor-operated appliance that is marked with both motor horsepower and full-load current, the motor full-load current marked on the nameplate of the appliance shall be used instead of the horsepower rating on the appliance nameplate to determine the ampacity or rating of the disconnecting means, the branch-circuit conductors, the controller, the branch-circuit short-circuit and ground-fault protection, and any separate overload protection.


Question is what does exception 3 typically apply to?
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
...
Question is what does exception 3 typically apply to?
"Appliance" is defined in article 100;
Appliance. Utilization equipment, generally other than industrial, that is normally built in standardized sizes or types and is installed or connected as a unit to perform one or more functions such as clothes washing, air-conditioning, food mixing, deep frying, and so forth.
Then Section 422 is devoted to them and it is in 422 that they first state that "motor-driven" appliances must follow article 430 rules, then they go on to describe non-motor driven appliances, like the frying and resistance heating type. So exception 3 is just reiterating what was already brought up in 422.
 

paulengr

Senior Member
I stand corrected on nonlinear loads.

https://www.ecmag.com/section/codes-standards/nonlinear-loads-havent-changed-definition-remains-same

There are rules and weasel worded informational notes for neutrals based on nonlinear loads but that’s it.

However as VFDs are or should be continuous loads (three hours or more) even though output fluctuates in an elevator application it certainly qualifies for the 125% rule for continuous loads. Most VFDs are powered continuously because the precharge circuits are not designed for routine power up. Many times installers on retrofits put the VFD on the output of a starter only to find it burns up frequently. The VFD manufacturers warn about this but the correct installation removes the contactor and powers it directly off the fuse/breaker. The exception is units with built in input contactors,


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