Why is FLC higher than FLA?

LPS

Member
Location
Florida
I’ve always assumed the FLC in the tables were higher than the typical FLA on the motor to allow a little extra circuit capacity in case a motor was swapped out with a less efficient one. Does anyone know why FLC is higher? If you do know, can you provide a reference? Thanks…
 

Besoeker3

Senior Member
Location
UK
Occupation
Electrical Engineer
I’ve always assumed the FLC in the tables were higher than the typical FLA on the motor to allow a little extra circuit capacity in case a motor was swapped out with a less efficient one. Does anyone know why FLC is higher? If you do know, can you provide a reference? Thanks…
I've always known it as FLC, not FLA. But then I'm just a Brit.............................:)
 

tom baker

First Chief Moderator
Staff member
I’ve always assumed the FLC in the tables were higher than the typical FLA on the motor to allow a little extra circuit capacity in case a motor was swapped out with a less efficient one. Does anyone know why FLC is higher? If you do know, can you provide a reference? Thanks…
That is what I read also by
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The code is a conservative code and the FLC values in Tables 430.247 through 430.251 are intended to be worst case and allow for the replacement of an existing motor with a less efficient motor without requiring new conductors and OCPDs.

You use the FLC from the tables to size the conductors and the branch circuit OCPDs for the motor, and you use the nameplate FLC to size the overload protection.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I've always known it as FLC, not FLA. But then I'm just a Brit.............................:)
The NEC agrees with you as Article 430 only used FLC. It never uses FLA.
Those two terms are used by many instructors to differentiate between the table current and the nameplate current.
I prefer to use "Table FLC" and "nameplate FLC" for that purpose when I teach as that leaves no question what current value you are talking about.
 
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Besoeker3

Senior Member
Location
UK
Occupation
Electrical Engineer
The NEC agrees with you as Article 430 only used FLC. It never uses FLA.
Those two terms are used by many instructors to differentiate between the table current and the nameplate current.
I prefer to use "Table FLC" and "nameplate FLC" for that purpose when I teach as that leaves no question what current value you are talking about.
Thank you Mr Don.
I watched the presentation by Mike Holt and the different tables. We usually have just the nameplate and not the tables.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Thank you Mr Don.
I watched the presentation by Mike Holt and the different tables. We usually have just the nameplate and not the tables.
You are required to use the table currents to size the conductors, and are permitted to use them to size the branch circuit OCPD.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Um....................I'm British.
I just use the FLC from the nameplate.
We are not permitted to do that under the rules of the NEC.
[/quote]430.22 Single Motor.
Conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current rating, as determined by 430.6(A)(1) ....

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. ....[/quote]
 

Besoeker3

Senior Member
Location
UK
Occupation
Electrical Engineer
We are not permitted to do that under the rules of the NEC.
430.22 Single Motor.
Conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current rating, as determined by 430.6(A)(1) ....

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. ....[/quote]
[/QUOTE]
Yes, I'm aware of that. Mike Holt explains it in detail and rather well.
 

LPS

Member
Location
Florida
I teach, so I was hoping someone had some inside info on the logic that went into coming up with the numbers… As electricians we just follow the rules, but when you teach it’s helpful when you can answer the questions that arise.
Thanks for the replies.
 

Besoeker3

Senior Member
Location
UK
Occupation
Electrical Engineer
Do you still use the horsepower unit on motors for the British market? Or do you follow the lead of the rest of Europe, and use kW for both electrical and mechanical power?
Yes we do. Power is just power. Not specifically mechanical or electrical.
When I was at secondary school, high school you would call it, we used 33,000 ft·lb for horsepower. But that about 60 years ago.
Now we just use kW. It's simpler. In fact, a lots of units are are much simpler. SI or International System.

US units are the unusual compared to the rest of the world.
 
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