article 440.32-- NEC 2005

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ecvolt

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In article 440.32 Single Motor-Compressor.what is it they mean with the wording---not less than 125 percent of EITHER the motorcompresor rated-load curent OR the branch circuit selection current,wichever is greater.I am not to sure were they are going with the branch circuit selectoin part of the question.Thank you
 
you have the current draw of the motor, and the size of the circuit breaker: whichever is the largest (FLC of motor or overcurrent rating of the breaker) you size the branch circuit conductors @ 125% of that number.
 
440.32

440.32

Thanks for your help. question? is it full load curent or name plate rated load curent that we are dealing with? So then if the RLC was say 24 ampers and the branch circuit selection was 30 amperes what size TW copper conductor would I use? note motor is singel phase no temperture or conduit fill factors are involved would it be 24 amps {RLC}times 1.25 = 30 ampres 310.16 says a number 10TW or would it be 30 ampres {branch circuit selection} times 1.25=40 ampres wich would be a number 8 TW copper conductor? Thanks again
 
i'm sorry, i said FLC above, but this code only says "rated-load current" -- So, we size against rated-load current (nameplate) or overcurrent device.


As to your other question; if you have a 30A overcurrent device, that is larger than the 24A RLC: according to 440.32, you would size your conductors to 125% of the largest, so

30x1.25 = 37.5A = #8 TW (Cu)

Is this homework? The last time I can remember having to use the TW ampacity chart was during a class I took. I've only laid eyes on TW insulated conductors once in my life, and they were pretty old.
 
I hope this helps !

I hope this helps !

For those interested 2008 is not "GREYED"

Just a reminded alot of good stuff is in 440.31 General

Well reading you question, and reading the Code, if you look at the total Code in its exact context your question can be answered better.

440.32 Single Motor-Compressor
Branch circuit conductors supplying a single motor-compressor shall have an ampacity not less than 125 percent of EITHER the motor-compresor rated-load curent OR the branch circuit selection current, whichever is greater.

Or maybe another example
If the VD Distance, enviroment, and other factors had to be considerd. Then yes your required Branch circuit selection current might be higher than 125% of the rated load current.

There was a fine thread on FLA verses Rated load current, 2-3 weeks ago,
or it was FLA Verse something else but nameplate related!

My first thought was that this doesn't happen much. Wiring a motor-compressor and the articles own example in the second paragraph and the FPN seems to go with my orginal thought.
Not many here have wired a Wye-start, Delta Run compressor. thats some Big Stuff!
OK its LAte, I can't recall any...

Motors all draw alot of amps to get started, it just so happens compressor motors generally take an even higher inrush eaiser, have a higher torque level due to this are built heavier to handle this bigger inrush of current.

quote=ecvolt]In article 440.32 Single Motor-Compressor.what is it they mean with the wording---not less than 125 percent of EITHER the motorcompresor rated-load curent OR the branch circuit selection current,wichever is greater.I am not to sure were they are going with the branch circuit selectoin part of the question.Thank you[/quote]
 
440.32

440.32

OK lets try this one lets say the Rated load curent is 18 amps the conductor is THHN what would you use in this case ?Also you are useing 30amp fuses.The reason I ask is because I saw a illistrtion in ECM magazine showing that you could use a #12awg THHN rated at 75degres c with up to 40 amp fuses! 2.25 times 18 amps .I would think it would be 30amps{fuses} times 1.25 = 40 amps and use a number 8 THHN @ 75 degres c I realize we could go the 2.25 if needed but still a number 12 THHN on a 40 amp fuse would still require a number 8 THHN 40x1.25 =50 amps . Acording to 440.32 WICH EVER IS GRATER the branch circuit selection is greater than the RLC Lets also asume all terminations are rated for 75degres c.Thanks for your help
 
ecvolt said:
OK lets try this one lets say the Rated load curent is 18 amps the conductor is THHN what would you use in this case ?Also you are useing 30amp fuses.The reason I ask is because I saw a illistrtion in ECM magazine showing that you could use a #12awg THHN rated at 75degres c with up to 40 amp fuses! 2.25 times 18 amps .I would think it would be 30amps{fuses} times 1.25 = 40 amps and use a number 8 THHN @ 75 degres c I realize we could go the 2.25 if needed but still a number 12 THHN on a 40 amp fuse would still require a number 8 THHN 40x1.25 =50 amps . Acording to 440.32 WICH EVER IS GRATER the branch circuit selection is greater than the RLC Lets also asume all terminations are rated for 75degres c.Thanks for your help
Click to expand...

Motors "break" our conventional thought process. Considering day in day out, we size the breaker to the wire we use. Motors totally break this standard rule of appliing electrical work and generally mess's with ones mind thought, while trying to learn and understand this application overall.

Rated load Current only appears by the Index in 440.4(A) and the Definition in 440.2.

Besides Grounding - 430 through 440 is the most sleep provoking reading one could ever want to take a nap by. (JMO)

OK first off think this way, Motors will most always apply 125%(heres another kicker-"Not always"), what type of motor gets this 125%, or where one needs to apply this boost for a wide varity of motors varies by the type, application, and their end use.

Yes in Fact there could well be smaller wire on a (larger than one thought required) breaker.
Well remember that the Breaker for a motor can be also Fused (a whole nother conversation).

I wanted to point to these last night but this is an A/C compressor.
not just a compressor, and frankly could not justify pointing to it till you added to your present thread.

This thread, note the illistration in #3 http://forums.mikeholt.com/showthread.php?t=97308
is very similar to your present thought, why is the wire smaller than the breaker.

Heres another good Example of what to look for when dealing with a (BUT its again only a A/C compressor). This again is related to you present why smaller wire.

http://forums.mikeholt.com/showthread.php?t=97306

The Forum has many past threads on motors that can be found using the Search, you can use an article number or small combintations of words that define your desired search, and try variables as well.

Good Luck with your Persuits.
 
440.32

440.32

Ok I think I figured this one out--------The statement from article 440.32 --Branch circuit conductors supplying a single motor compresor shall have an amapcity not less than 125 percent of either the motor compresor rated load current OR!!! the branch -circuit selection current,wichever is greater.My confusion came in the part 'or the branch -circuit selection current,wichever is greater.I thought that the wording of branch circuit selection current was in reference to 440.22 BUT IT IS NOT!The branch circuit selection is nothing I determine or even calculate it is provided by the manufacturer of the motor compresor SEE 440.4 C.So if there is no BRANCH -CIRCUIT SELECTION CURENT ON THE NAME PLATE THAN GO BY THE RLC . IF THERE IS A BRANCH -CIRCUIT SELECTION CURENT ON THE NAME PLATE THEN COMPARE IT TO THE RLC AND USE THE LARGEST TIMES 125 PERCENT.NOTHING AT ALL TO DO WITH 440.22.It is not the over curent device [which IS SIZED FROM 440.22 !!]but rather Branch -circuit Selection current or rated load curent that determines the proper conductor size.IT is all in the verbage .Thanks for everyone's Help ecvolt
 
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