Full Load Amps? 2

[cgap]

I am trying to determine the load being added to the electrical system - equipment states 200A Full Load and 25A Largest Motor
When a piece of equipment states "Full Load" Amps, is that the same as "Starting Amps" or "Running Amps"?
Thanks!

 

[electricpete]

Full load amps would be comparable to running amps... IF you are running at full load.

Full load amps will be far less than starting amps.

 

[kamalpanda]

Normally equipments designed for motor starting are to be specified during ordering stage itself.

as per example if you are ordering a Generator set of 100KW it does not mean u can be able to connect a 75 KW (Less than the generator rating)motor to it unless otherwise specified during design stage .The manufacturer designs its equipments considering motor starting with capability of momemntary overloading.

Now we come to ur question:

at no point the full load amps of an equipment states its starting amps. Especially for inductive loads like motors where starting current is very high normally two ratings are mentioned.

1) rated Current or full load amps.
2) Starting Current in times of rated current.

the starting current phenomenon is also observed in Transformer loads. But in transformer it is the inrush current whose nature is different from the starting current in case of motor and depends on the point on the waveform where voltage is applied to the transformer.

Hope this clarifies ur doubts.

 

[PacificSteve]

I am not an expert, but the following has always been my impression, and it would be great if someone else can verify these:

FLA is very similar to RLA, running load amps.

LRA locked rotor amps, is very similar to starting inrush current, i.e. when the motor is dead stopped prior to starting, current needed to get it moving is similar to if the rotor where "locked".

I believe the reason they give use the largest motor size if for code sizing on overload protection, which goes something like the FLA plus 50%*largest motor in the equipment.

PacificSteve

 

[electricpete]

Good point Pacific Steve that cgap has been given a composite load 200A including a number of smaller loads. The largest motor in the bunch being 25A. Largest inrush would be based on starting of that largest motor i.e. approx 175A + 6*25A. FLA is a term used to describe a single motor. I don't know what it means in this context other than presumably it is the maximum steady state load.

I agree with you Steve that LRA is identical to starting current. FLA is running current under nameplate conditions of loading and voltage. I haven't heard the term RLA.

 

[PacificSteve]

RLA being running load amps. Often confused with LRA.

PS

 

[jbartos]

Suggestion to cgap (Electrical) May 7, 2002 marked ///\\I am trying to determine the load being added to the electrical system - equipment states 200A Full Load and 25A Largest Motor
///NFPA 70-1999 National Electric Code in Art. 430-24 suggests to add 25% of the largest motor current, i.e. 200A + 0.25 x 25A=206.25A\\When a piece of equipment states "Full Load" Amps, is that the same as "Starting Amps" or "Running Amps"?
///Full-load amps = rated amps, see manufacturer's catalogs, e.g. Baldor, Reliance, etc.
Starting amps are close to inrush current and locked rotor amps if no voltage reduction is applied accross the motor terminals, e.g. a wye-delta starter.
Running amps can be full-load amps, greater than full load amps, if the motor has the service factor greater than one or lower than full load amps if the shaft load is smaller than the rated shaft horsepower.\\\

 

[electricpete]

good last point by jbartos. Motor certainly may draw a current much different than FLA, depending on it's loading.

Perhaps that's the distinction between the terms FLA and RLA. FLA is a nameplate number for rated loading and voltage conditions. RLA would presumably be a value corresponding to actual field loading and voltage conditions.

 

[rbulsara]

nzlad:

Also keep in mind that the feeder size is the conductor size are indicated by NEC 430-24 how ever the overcurrent protection may be larger than that to allow for starting current which is explained in 430.53.

Swichboard sizing is somewhat art and some science. I would size the swichboard such that it can provide maximum possible continuous load (include diversity, which is not an exact science) and have some room for growth.

 

[aolalde]

Back to the original post, this equipment has several internal motors and electrical loads. 200 Amperes at Full load and 25 Amperes largest motor.

Then the maximum Running Current is 200 Amperes. If the equipment is partially loaded that running current could be reduced.

The starting current will depend on the machine design, probably some motors start and stop during the process being partially loaded but the maximum inrush expected is when the 25 Amperes motor starts, that means 25*(~7)= 175 Amperes plus the previous load which has to be (200-25)= 175 amperes maximum.

Then the maximum inrush expected is 2*175= 350 amperes.

 

[jbartos]

Comment on cgap (Electrical) May 7, 2002 marked ///\\I am trying to determine the load being added to the electrical system - equipment states 200A Full Load and 25A Largest Motor
///The statement implies that there is a 25A largest motor in the 200A Full Load total. There may be many smaller motors drawing less than 25A.\\\

 

[skiier]

FLA is simply the maximum "steady" state current this unit can draw. The term "running amps" is rare but also means the same as FLA. This value of FLA is simply used to "rate" the conductor that feeds this piece of equipment. The starting current is the maximum "transient" current that this machine can produce at start-up. The starting current determines the fusing for your machine and depending on your type of equipment the starting current can be as much 300% of the FLA for your machine.
Simple explanation huh?

 

[ScottyUK]

Hi skiier,

[blue]starting current can be as much 300% of the FLA for your machine[/blue]

Only 3x FLA? It's quite common to se 6-8x FLA as starting current. Some particularly unamenable motors take up to 10x FLA, although these are thankfully not too common - usually mill duty motors with very high initial torque capability.



-----------------------------------

Start each new day with a smile.

Get it over with.

 

[jbartos]

Comment on the previous posting:
Please notice that the squirrel-cage induction motor starting amps are linked to its locked-rotor amps and NEMA Code Letters, if the motor complies with NEMA Standards.
Reference, e.g.: NFPA 70-2002 National Electrical Code (NEC) Table:
Table 430.7(B) Locked-Rotor Indicating Code Letters
Code Letter - Kilovolt-Amperes per Horsepower with Locked
Rotor
A 0- 3.14
B 3.15 – 3.54
C 3.55 – 3.99
D 4.0 – 4.49
E 4.5 – 4.99
F 5.0 – 5.59
G 5.6 – 6.29
H 6.3 – 7.09
J 7.1 – 7.99
K 8.0 – 8.99
L 9.0 – 9.99
M 10.0 – 11.19
N 11.2 – 12.49
P 12.5 – 13.99
R 14.0 – 15.99
S 16.0 – 17.99
T 18.0 – 19.99
U 20.0 – 22.39
V 22.4 and up
==============
This means, for example, that a motor with NEMA Code Letter A may have starting current from 0 A to about 3 x FLA.

 

[ScottyUK]

jB,

Thanks for a useful post.



-----------------------------------

Start each new day with a smile.

Get it over with.

 

[GGOSS]

Hello cgap,

Full Load Amps are drawn when 100% load is applied.

Run Load Amps are the amps drawn under normal running condition.

Starting Amps occurs during the starting of a perticular machine.

Often Full Load Amps (FLA or FLC) are confused with Run Load Amps (RLA).

Relating this to a motor circuit may help. Prior to selecting a motor a mechanical engineer will perform some calculations to determine how may Nm of torque are required to run the load. This defines the expected RLA.

When selecting a motor however, the mechanical engineer has to select between standard kW/hp sizes and therefore choses a motor that develops an amount of torque (Nm) equal to or greater than that required to run the load. In the main, the selected motor produces more torque than is actually required and therefore the RLA is generally less than FLA.

Hope the above helps.

Regards,
GGOSS

 

[skiier]

Thanks for the clarification ScottyUK. I was just giving an example to cgap.
There seems to be quite some confusion on the terms used. I think that everyone understands the concept of these terms in the same way but the language that they use to explain these terms is different. You say "to-may-to" I say "to-ma-to", you get the idea.
RLA is the "running load amps" as I have always known it in Ontario and to me this is also the FLA or "full load amps". I know that you can say that RLA is dynamic and varies with load and I totally agree. But in most applications the RLA is transient and is of little consequence when the FLA is the maximum load we are concerned with.
What is the one place that we are most concerned with terms and what is the one time that these terms have any real practical use/application? Why on a machinery "Nameplate" of course.
When I look at a nameplate at an install I look at 3 things on that nameplate: Voltage/Phases, FLA, and maximum fuse/type (if available). If the maximum fuse/type is missing I duplicate the equipment's power feeder fuses at the point of supply. I am not going thru that machine and performing a load calculation to determine the characteristics and size of the fuses on my feeder conductors. It has already been done by the equipment manufacturer. I am not concerned with the dynamic RLA as it's "characteristics" are taken into account by the "maximum fuse/type" on the nameplate. I know the fuse type so now all I need to know is the FLA to determine my feeder conductors for the machine.
If cgap had all this information on his nameplate he wouldn't be confused and he wouldn't be posting this question.