Elevator RLA vs FLA and sizing feeders/OCP

[Alan Vogel]

I have researched on many websites and through many of Mike Holt's forums and have found varying answers and views on this topic. When designing new projects we only get the horsepower rating of the elevator during such an early stage of the project, but a crucial stage in design. We typically base the elevator circuits/feeders off of the horsepower rating only and NEC 433.250 FLC numbers.

I received the below information from TK elevator which lists their standard motor information.

40HP
208V 3ph
"Motor Nameplate Data"
RATED AC AMPS: 122.5

"Full Load Up High Speed"
Motor AC amps: 172
Control Amps: 4
Total Amps: 176

My confusion (and it seems like everyone else is confused because I find varying answers across the forums/websites) is which amperage is used to base feeder/branch circuit wiring and OCP breaker sizing? It seems unrealistic to base wire/OCP sizing for a 40hp motor using the 172 amps which is characteristic of a 60hp motor...doesn't make sense. Also, we typically would not have the 172 motor amps, 4 control amps and the 176 total amps available to us since the elevator vendor is selected during construction and not design phase.

Any clarification you could provide would be greatly appreciated. In addition to clarifying FLA vs RLA...seems like many forums are confused on this as well. May be a good instructional video clip for Mike!

 

[Ingenieur]

Ref NEC 620.13
basically sized like any other motor 430.22 A-E
motor nameplate table 430.22.E plus control ckts

 

[Alan Vogel]

After digging further, TK elevator includes a document that lists recommended breaker sizes for various horsepowers and soft starting or across the line starting. For the 40hp indicated at the start of this thread, they recommend a 250A breaker for soft starting and 300A for across the line based on NEC (per their footnotes). These values are clearly based on the 122.5A which was indicated to be the motor nameplate FLA or "nameplate rated ac amps" as they put it...not sure NEC recognizes "rated ac amps".

 

[steve66]

After digging further, TK elevator includes a document that lists recommended breaker sizes for various horsepowers and soft starting or across the line starting. For the 40hp indicated at the start of this thread, they recommend a 250A breaker for soft starting and 300A for across the line based on NEC (per their footnotes). These values are clearly based on the 122.5A which was indicated to be the motor nameplate FLA or "nameplate rated ac amps" as they put it...not sure NEC recognizes "rated ac amps".

This always confuses me too. Referring to 430 always brings us to table 430.22(E). I assume we use the 2nd row for elevators, but what is the rating of the motor? We are lucky to get a HP rating out of the elevator people, much less what the duty cycle rating of the motor is.That leaves us guessing anywhere between 85% of the FLA and 140% of the FLA.

Why do you say the values were clearly based on the 122.5A? For a 40HP motor, my table gives 120 amps FLA (that matches), but a breaker size of 175 amps, not 300?

 

[Smart $]

This always confuses me too. Referring to 430 always brings us to table 430.22(E). I assume we use the 2nd row for elevators, but what is the rating of the motor? We are lucky to get a HP rating out of the elevator people, much less what the duty cycle rating of the motor is.That leaves us guessing anywhere between 85% of the FLA and 140% of the FLA.

Why do you say the values were clearly based on the 122.5A? For a 40HP motor, my table gives 120 amps FLA (that matches), but a breaker size of 175 amps, not 300?

430.22 establishes the minimum conductor ampacity... not the maximum SC/GFP rating.

120A x 250% = 300A

 

[steve66]

430.22 establishes the minimum conductor ampacity... not the maximum SC/GFP rating.

120A x 250% = 300A

That answers the question about the OCP.

But what about the rating of the motor?

 

[Smart $]

...
But what about the rating of the motor?

What about it?

 

[Alan Vogel]

Steve66, I use 30&60 minute rating motor because as you mentioned above, we rarely get HP during the design phase let alone the actual duty rating of the motor, so we stick to worse case. Interestingly, I just received 3 elevator vendor quotes on a project which one of them (Schindler) actually stated the motor was rated 30 & 60 min. for NEC conductor sizing.

Keep in mind, NEC requires the motor "nameplate" FLA to be used for low speed, high torque, multi-speed, and other than continuous duty motors for sizing conductors and SC/GFP, so you cannot use NEC 120 FLC for elevators, you have to base your calculations on actual motor nameplate FLA...which is challenging since typically this information is not known during design phase of a project.

 

[steve66]

What about it?

If we don't know the motor's duty cycle, do we size for continuous duty (125%), or intermittent duty with table 430.22E, and if we use the table, the rating percentage for a passenger elevator varies anywhere from 80% to 140%. So which row to use when, for example, all you know is you are getting a 25HP motor?

Keep in mind, NEC requires the motor "nameplate" FLA to be used for low speed, high torque, multi-speed, and other than continuous duty motors for sizing conductors and SC/GFP, so you cannot use NEC 120 FLC for elevators, you have to base your calculations on actual motor nameplate FLA...which is challenging since typically this information is not known during design phase of a project.

You lost me there. Sometimes I can get a HP rating from the elevator company, and with that I can usually look up the FLA in the motor tables, and it should be pretty close to the nameplate FLA.

 

[Ingenieur]

For a single elevator

If supplying a single motor table 430 22 E based on nameplate
seldom the case, the feeder usually serves a controller or transformer (iso or otherwise)

controller
controller nameplate plus other connected loads
controller nameplate may be derived from motor i rms (intermittent duty) plus control load (I usually use the cntl xfmr va rating)

transformer
nameplate i plus other connected loads

these runs are often long (basement to rooftop/penthouse) so V drop is a factor

 

[Smart $]

If we don't know the motor's duty cycle, do we size for continuous duty (125%), or intermittent duty with table 430.22E, and if we use the table, the rating percentage for a passenger elevator varies anywhere from 80% to 140%. So which row to use when, for example, all you know is you are getting a 25HP motor?

If all you have is HP rating, you can't go wrong if you size conductors as if motor will be a continuous duty motor (140%).

As to SC/GFP, you are only required to use nameplate rating if the motor is built for low speed or high torque where nameplate current rating has higher FLA than table... but that just raises the maximum breaker/fuse rating, so if you size to 250% of table value you shouldn't be so far off that you drop into the nuisance trip range.

If you do this and it comes to pass performance is insufficient, then you correct and back charge the entity that should have provided exact spec's to begin with. JMO

 

[Alan Vogel]

The original point of this thread was the elevator company providing "full load up current" in their submittal of 172a which is substantially higher then motor nameplate rating. In short, this value is not used in determining sc/gfp rating or conductor sizing; Motor/controller "nameplate" should be used for sizing (plus adjustment factors like vd, etc.)...agreed? Its confusing that TK states "rated ac amps" for motor nameplate FLA but goes on to give a "full load up amps" value. Sizing ocp and wiring based on 122A and chaning to 172A during submittal stage would result in unwanted change orders to increase size of ocp and wire size. Hopefully im being clear with my confusion.

 

[Geon_W]

After digging further, TK elevator includes a document that lists recommended breaker sizes for various horsepowers and soft starting or across the line starting. For the 40hp indicated at the start of this thread, they recommend a 250A breaker for soft starting and 300A for across the line based on NEC (per their footnotes). These values are clearly based on the 122.5A which was indicated to be the motor nameplate FLA or "nameplate rated ac amps" as they put it...not sure NEC recognizes "rated ac amps".

where can I find this document?