FLA for an Industrial Machine

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fifty60

fifty60

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Is it correct for a manufacturer to use the actual measured FLA of a machine, or do they have to use the summation of all the rated loads that could be on at the same time. The rated loads approach sounds straight forward enough, but does not always give the accurate representation of the machine FLA.

For Example:

I have a machine that has refrigeration compressors, nichrome wire heaters, immersion boiler heaters, and an air circulator fan. All of these load could be on simultaneously, but not at their full rated load. For example, the compressor can draw 15A at rated load, but with the heaters on 100% they would be drawing less than the 15A because although they are on, they are not under any load. The compressors eventual time out and will shut completely off, but for a brief period of time (approximately 1 minute) they will be on simultaneously with the heaters.

For a situation like this, am I able to physically measure what the full load amps are for the machine, which will appear on the nameplate, and also use that to size my equipment OCPD?
 
The answer to your question would appear to be defined by whatever standard you are using to build the equipment.

UL508a and NFPA79 both have well defined methods of determining the FLA of a machine.

As a practical matter, they are essentially the same, and what you want to do would not be allowed by either of them.

If it is being designed to some other standard, maybe that standard would allow for it.

ETA: I think you could use that data to select a rating for your OCPD as the numbers in those standards are the maximum value allowed, and I don't recall there actually is a minimum for the OCPD. However, that would not affect the calculation for the machine FLA.
 
The relevent standard would be IEC 61010 (also UL 61010). Here is what the document says:

The equipment shall be marked with the following information:

The maximum RATED power in watts, or the maximum RATED input current, with all accessories or plug-in modules connected.

The standard defines RATED as:
RATED: quantity value assigned, generally by a manufacturer, for a specified operating condition of a component, device or equipment.

The refrigeration compressors I use do not have any RLA marked on the nameplate. Would it be reasonable to use the actual TESTED FLA under the most extreme condition to calculate the FLA? I would be the OEM of the equipment, so would the FLA be assigned by me for the specified operating condition of the equipment?
 
After studying NEC 440 again, since the compressors are not marked with an RLA, I have to put an RLA on the final equipment that uses the compressors. This RLA is determined by the rated operating conditions of the equipment. I can use the tested load current of the compressors to sum the equipment FLA as long as I am using the RLA that I put on the name plate of the end equipment...
 
But strictly reading 440.4(B), I do not even have to put the FLA on the nameplate. I have to put the volts, frequency, number of phases, minimum circuit ampacity, max rating of the branch OCPD, and the SCCR. It does not mention anything about FLA.

The 61010 is not always a requirement, so when it is not, all I have to follow is the NEC and 440 is the relavent article...so looking at it this way I can put the max tested FLA on the equipment...or not any FLA if I wanted to...
 
The NEC is not an equipment standard.

If the standard you want to follow says you can do so than you can. I am not familiar with the standard you are asking about.
 
Can you please elaborate a little bit about what you mean by it is not an equipment standard? 440 specifically calls out "motor driven air conditionaning and refrigerating equipment and to the branch circuits and controllers for such equipment"

I have to use the NEC to define the branch circuit that that the equipment will be connected to, right?
 
fifty60 said:
Can you please elaborate a little bit about what you mean by it is not an equipment standard? 440 specifically calls out "motor driven air conditionaning and refrigerating equipment and to the branch circuits and controllers for such equipment"

I have to use the NEC to define the branch circuit that that the equipment will be connected to, right?
Click to expand...

440 mostly covers the circuits that go to the equipment, not the actual equipment. that is fairly typical of the way the NEC is.

430 does not tell you how to design motors. just how to wire them up.

look what the first paragraph says.

I. General
440.1 Scope. The provisions of this article apply to electric
motor-driven air-conditioning and refrigerating equipment and
to the branch circuits and controllers for such equipment. It
provides for the special considerations necessary for circuits
supplying hermetic refrigerant motor-compressors and for any
air-conditioning or refrigerating equipment that is supplied
from a branch circuit that supplies a hermetic refrigerant
motor-compressor.
Click to expand...

As best I can tell the only thing that it requires of the equipment is one or more nameplates. The rest of the design of the equipment is pretty much open.
 
If This Helps ?

If This Helps ?

We build custom machi9nery for several industries. I went through a similar discussion recently with the company owner. I has specified a FLA for the machine we were shipping, however the customer had already prepared the site for a supply much smaller than I specified.
After much research, we discovered we could calculate the actual run times of each part of the machine and de-rate the FLA, since the machine will not run all parts at the same time. I had the mechanical engineers come up with a spreadsheet that showed the timeline percentages of operation of all motors that would be running or could run at a givin time. I took that as the max and figured the FLA accordingly. It amounted to about 60% of the original FLA rating I came up with at first...
 
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