Sizing automated machinery for nameplate and disconnect ratings

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calebxx12

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Location
United States
Hello Everyone,

Interesting question for you I guess. We build automated assembly machinery, and have been for 20+ years now. We have a lot of data on past current draws of machines that we have made and have been sizing new machines based on that data and NEC. Recently we got into the NFPA a little more and sized the machine to that, it came to a rather large current rating when the machine is only drawing around 12 amps at full operation (sized for 60A).

What is the proper way to make a nameplate? Based on the FLA rating of everything or could we make it small, say 30A as apposed to 70A?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I would say make the nameplate what you believe it should be. But be aware (and I infer that you are already) that when we made design decisions (e.g., breaker and wire sizes), we are required to use the tables in the NEC, and not use the information on the nameplate. That makes our designs perhaps a bit more conservative than they need to be, but that is the way the NEC's authors want it to be.

Welcome to the forum.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
UL508a 49.2

NFPA79 17.4.2

You pretty much are required to state the FLC as worst case of all the loads that might be on at the same time, and not what it might really be.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
UL508a 49.2

NFPA79 17.4.2

You pretty much are required to state the FLC as worst case of all the loads that might be on at the same time, and not what it might really be.
But notice the important point of this statement, "all loads that might be on at the same time", that is different from "all loads in the machine", which might have been what you were doing that got you to a seemingly ridiculous value on the nameplate. The nameplate only needs to address the worst case scenario.
 

calebxx12

Member
Location
United States
I guess I can rephrase this a bit. Say we have a machine that could be running everything at the same time (most likely will not, but there is a slight chance) and we got a total of 300A adding all the FLA of the devices. We have measured data the says the machine is only drawing 50A. Is there anything that is a workaround on article 670 (which is the NEC article this falls under)? It is a huge expense to go up in current for something that does not seem necessary.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I guess I can rephrase this a bit. Say we have a machine that could be running everything at the same time (most likely will not, but there is a slight chance) and we got a total of 300A adding all the FLA of the devices. We have measured data the says the machine is only drawing 50A. Is there anything that is a workaround on article 670 (which is the NEC article this falls under)? It is a huge expense to go up in current for something that does not seem necessary.

670.3 Machine Nameplate Data.
The full-load current shown on the nameplate shall not
be less than the sum of the full-load currents required for
all motors and other equipment that may be in operation at
the same time under normal conditions of use. Where unusual
type loads, duty cycles, and so forth require oversized
conductors or permit reduced-size conductors, the required
capacity shall be included in the marked "full-load current."
Where more than one incoming supply circuit is to
be provided, the nameplate shall state the preceding information
for each circuit.
IMO, you can't avoid the requirement to add up the FLC of all the devices that might be on at the same time.

There are some special cases in article 430 where you can cheat on the conductor ampacity requirements that I think you can take advantage of, if applicable, but they are kind of oddball situations.

It seems odd to me that a machine that actually takes 50A in normal operation would add up to a calculated load of 300A. Is it possible that you have oversized motors and other components as part of your design?
 

under8ed

Senior Member
I would say make the nameplate what you believe it should be. But be aware (and I infer that you are already) that when we made design decisions (e.g., breaker and wire sizes), we are required to use the tables in the NEC, and not use the information on the nameplate. That makes our designs perhaps a bit more conservative than they need to be, but that is the way the NEC's authors want it to be.

Welcome to the forum.

I don't know if I understand this correctly. When a new machine needs installing, which is unlike any other we have seen previously: where else are we to calculate feeder design from other than the nameplate. The nameplates on automated machinery have been both my friend & foe over the years as an installer. I am not scrutinized by an inspector, and the engineers give me a fairly free range to make the call on feeds due to my ability, (or luck), at providing cost effective installs. At times I use intuition over the data provided, (the more complicated the operation, the more skewed the dataplate). There have been installations where the incoming conductors are considerably small for the machine's main breaker. Many machines are designed for overseas use, and the calculations may be different. I do feel that many may be using full loads totaled with no regard of "normal operation". Another post mentioned over-design, I see this often. The purpose of this is likely to be durability, if they use a 5 hp motor to do only 3 hp work, it is probably a valid argument: but it reeks havoc for our purpose.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I don't know if I understand this correctly. When a new machine needs installing, which is unlike any other we have seen previously: where else are we to calculate feeder design from other than the nameplate. The nameplates on automated machinery have been both my friend & foe over the years as an installer. I am not scrutinized by an inspector, and the engineers give me a fairly free range to make the call on feeds due to my ability, (or luck), at providing cost effective installs. At times I use intuition over the data provided, (the more complicated the operation, the more skewed the dataplate). There have been installations where the incoming conductors are considerably small for the machine's main breaker. Many machines are designed for overseas use, and the calculations may be different. I do feel that many may be using full loads totaled with no regard of "normal operation". Another post mentioned over-design, I see this often. The purpose of this is likely to be durability, if they use a 5 hp motor to do only 3 hp work, it is probably a valid argument: but it reeks havoc for our purpose.
The code does not give you a choice. Look at what the requirements are for sizing motor feeders in article 430. You are just plain not allowed to downsize the conductor ampacity from what is required there, even if your employer allows you to do so. Cost is not part of the code either.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I don't know if I understand this correctly. When a new machine needs installing, which is unlike any other we have seen previously: where else are we to calculate feeder design from other than the nameplate. The nameplates on automated machinery have been both my friend & foe over the years as an installer. I am not scrutinized by an inspector, and the engineers give me a fairly free range to make the call on feeds due to my ability, (or luck), at providing cost effective installs. At times I use intuition over the data provided, (the more complicated the operation, the more skewed the dataplate). There have been installations where the incoming conductors are considerably small for the machine's main breaker. Many machines are designed for overseas use, and the calculations may be different. I do feel that many may be using full loads totaled with no regard of "normal operation". Another post mentioned over-design, I see this often. The purpose of this is likely to be durability, if they use a 5 hp motor to do only 3 hp work, it is probably a valid argument: but it reeks havoc for our purpose.

This is the problem that faces the OP. He knows 99% of the time his machinery will only draw 12 amps, but it could require 48. He needs to tell us via the label what the MCA and MOCP needs to be. That is what we install to the equipment. No choice. Not much of a headache at this range but, as you know, a big difference if we are looking at 120 vs 480 amps.
 

under8ed

Senior Member
The code does not give you a choice. Look at what the requirements are for sizing motor feeders in article 430. You are just plain not allowed to downsize the conductor ampacity from what is required there, even if your employer allows you to do so. Cost is not part of the code either.

So many years working in one facility have possibly ruined me from working elsewhere. I suspect the engineers here feel that once a motor is built into a piece of equipment, it is just that.. a piece of equipment with a dataplate. Besides that, the amount we skimp from the listed KVA or amperage of automated machinery is not likely compromising codes if they were all properly sized within the machine. Right or wrong, I have been taught that I can attempt to feed with anything that is properly protected; with the caveat being that it will be egg on my face if I need to replace it with a larger size later.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
So many years working in one facility have possibly ruined me from working elsewhere. I suspect the engineers here feel that once a motor is built into a piece of equipment, it is just that.. a piece of equipment with a dataplate. Besides that, the amount we skimp from the listed KVA or amperage of automated machinery is not likely compromising codes if they were all properly sized within the machine. Right or wrong, I have been taught that I can attempt to feed with anything that is properly protected; with the caveat being that it will be egg on my face if I need to replace it with a larger size later.

as long as the conductors are protected I do not think you did anything unsafe. It is still not to code.

I am not sure just what you mean by "compromising code". You either met the minimum requirements of the code or you didn't.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
FWIW.
Label Reads:

FLA 12
MCA 15
MOCP 30

My thoughts are as long as the installer provides the MCA to the equipment, I don't care if the Over Current Protection is 15, 20, 25, or 30. The only violation would be if they exceeded 30 or did not provide the MCA.

machinery does not typically have nameplates like this though.
 

under8ed

Senior Member
Labels I come across are often in another language as well, Of course, many terms are universal; but not all. Usually the most definitive is the KVA, sometimes power is only listed in KW. I am working tomorrow, I will look for an example of one that lists more power than I supplied.
 

calebxx12

Member
Location
United States
Thanks for the replies guys.

It looks as though there is no real "cheat" to get around some of these issues. We will have to continue sizing the machine accordingly to 670 and NFPA 79. Seems pretty crazy we are getting such differences in total current ratings, maybe the manufactures FLA ratings are off (not all devices we use are motors).
 
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