Machine's FLA Derived From..

[fifty60]

I am interested to know if using tested Full Load Amps is generally acceptable.

Do you have to use all simultaneously active components RATED amps, or are you actually able to use the maximum tested amps?

I am used to using the rated load of all the components that can be on simultaneously. However, the conditions that are present when all the components are on at the same time do not result in the maximum rated current draw for each component.

Using the rated values for everything, for example, gets you 27A which means a 35A minimum and 8AWG. But when the machine is tested it, goes over 24A which would fit on a 30A circuit with 10AWG wire.

 

[petersonra]

If you are following a standard like UL508a or NFPA79 (just examples - it could be any standard you are claiming compliance with), you have to make the calculation the way the standard tells you to, or you can't legitimately claim compliance to that standard.

If you are not claiming compliance to a specific standard, you can calculate it anyway you see fit.

In fact, you can put on a number that is not in compliance and lie about it and claim it complies.

Having said that, the NEC does not allow one to use the nameplate current as a means of determining the ampacity of the conductors feeding a machine. The nameplate is a convenience to the end user.

if the machine as a whole is listed by a NRTL you might be able to get them to accept the idea, but it seems doubtful as it would be very confusing to an end user.

 

[fifty60]

Thanks for the information. I do not understand the part about not being able to use the nameplate to size the ampacity of the conductors feeding the machine. What is the end user supposed to use then?

Looking at article 215 I see that it uses the wording "continuous and noncontinous loads", but does not say anything about "rated" loads. Please direct me to any other articles that may be of help here.

I understand that compliance with a particular code is different than compliance with NFPA 70. The end goal is to be compliant with the standard I am using and with what is relevant in NFPA 70.

Also, on a side note, why does the forum spell checker call out "Ampacity" as being spelled wrong.

 

[GoldDigger]

Also, on a side note, why does the forum spell checker call out "Ampacity" as being spelled wrong.

Are you sure that it is the Forum spellchecker and not one tied to your browser?

ampacity
Ampacity
Interestingly enough, it only complains when the first letter is capitalized.
I can add it to my dictionary by right clicking, which makes me think that it is a browser (Firefox) function, or else that the Forum database maintains a spell check dictionary delta for each member.

 

[fifty60]

I can get some warm and fuzzy assurance from my NRTL inspector, but I still have to comply with NFPA 70. My initial concern is that whatever I use allows me to size my wiring correctly.

A general rule of thumb is to always size conductors at an ampacity 125% or more of the rated load. But there are exceptions to this, right? My machine has refrigeration compressors in it. Am I immediately allowed to use the exception found in 240.4G to go to Article 440 part III and IV?

I want the FLA to be as close to what is actually there as possible. At the same time, I want to account for a little bit of tolerance in the equipment. With a 10% amp tolerance, if I say the FLA is 24A, that gives a range between 21.6A to 26.4A. I size the OCPD to 30A, and use 10AWG wire. Am I out out of compliance with NFPA 70 when I go above 24A by 10%?

If so, I would have to size my wire off of 26.4A. Using article 440, I can use the largest compressor plus the sum of all the other simultaneous loads. This is definitely an advantage for sizing refrigeration equipment. Am I looking at this correctly?

 

[petersonra]

Thanks for the information. I do not understand the part about not being able to use the nameplate to size the ampacity of the conductors feeding the machine. What is the end user supposed to use then?

The code tells you how to size a feeder or a branch circuit in article 220, and how to size the over current protection in article 240 (430 for motors).

430.26 might allow you to do what you want, but you have to get permission from the AHJ to do so.

Otherwise, the installation has to follow 430.24 for determining the conductor size feeding the machine.

430.24 Several Motors or a Motor(s) and Other Load(s).
Conductors supplying several motors, or a motor(s) and other
load(s), shall have an ampacity not less than the sum of each
of the following:
(1) 125 percent of the full-load current rating of the highest
rated motor, as determined by 430.6(A)
(2) Sum of the full-load current ratings of all the other
motors in the group, as determined by 430.6(A)
(3) 100 percent of the noncontinuous non-motor load
(4) 125 percent of the continuous non-motor load.

There are some exceptions that follow 430.24 but none appear to apply to your case.

Looking at article 215 I see that it uses the wording "continuous and noncontinous loads", but does not say anything about "rated" loads. Please direct me to any other articles that may be of help here.

That's because the NEC does not care what the "rated" load is of the machine.

I understand that compliance with a particular code is different than compliance with NFPA 70. The end goal is to be compliant with the standard I am using and with what is relevant in NFPA 70.

I think it would be better to look at it this way. the machine does not have to comply with the NEC. It does have to accommodate NEC requirements. That may seem like spliting hairs but it is an important distinction.

Also, on a side note, why does the forum spell checker call out "Ampacity" as being spelled wrong.

I did not know it had a spell checker. Most spell checkers are just lists of words. if the word you typed in is not there it is flagged. Many technical words are not found in these lists. Usually there is a way to add a word to the list.

 

[GoldDigger]

I did not know it had a spell checker. Most spell checkers are just lists of words. if the word you typed in is not there it is flagged. Many technical words are not found in these lists. Usually there is a way to add a word to the list.

Take a look at http://boards.straightdope.com/sdmb/showthread.php?t=644858 for a discussion of this.
The spell checker in most web browsers is not active on single line text entry fields or boxes but is active on multiline text boxes like the Post and Edit boxes in vBulletin. That may be why you are not used to seeing your browser's spell check functions.
As noted in that thread, if the underlining shows up before you submit, it has to be coming from the browser.

Apparently there may also be a spell check option with vBulletin, but I doubt that this Forum implements it.