220.82(C) 100% of the nameplate rating
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wwhitney
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- Berkeley, CA
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You've certainly left something out, as the MCA is 36.1, and if the only loads were 12.4 RLA and 2.3 FLA, the MCA would be 12.4*125% + 2.3 = 17.8. Odd that the nameplate doesn't indicate what the other loads are. The best you can say is that the sum of the loads would be at most 36.1 - 12.4*25% = 33A.
However, I expect most people would just use the MCA of 36.1. That is certainly the only single number printed on the nameplate that comes close to a rating for the complete unit.
Cheers, Wayne
However, I expect most people would just use the MCA of 36.1. That is certainly the only single number printed on the nameplate that comes close to a rating for the complete unit.
Cheers, Wayne
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I would take the 36 amp min circuit and divide by 125%.... 28.8 amps
Thanks for the quick responses, this is like the 10th one I have seen like this lately.
Yeah thats usually my go to I suppose I'll stick with that.
wwhitney
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That's clearly non-conservative, as the MCA is from a formula of the form: MCA = 125% * A + B + C + D etc. Dividing the whole thing by 125% would give you A + 80%*B + 80%*C + 80%*D etc. Whereas we want, as a minimum, A + B + C + D.
Hence my suggestion of taking MCA - 25% * RLA. The RLA is likely the largest motor load, the "A" in my example above. So subtracting off 25% of RLA gets us from MCA to A + B + C + D. And if we are wrong, and some other motor is larger than the RLA, the answer get is conservative.
Cheers, Wayne
Glad I am not the only one that this is odd.
Perhaps I'll call their tech support and see what I missed.
Valid point thanks but article 220 can't expect disassembly of the 'MCA' for a load calc, when a Run Load Amps (RLA) and or Full Load Amps (FLA) are provided? Is that not the meaning of those terms?
Perhaps I'll call their tech support and see what I missed.
Tech support got back to me and confirmed the 14.7 amps is normal, and commented thats often the case with these traditional staged equipment. I asked how they calculated the MCA & MOP numbers but he did not know but speculated its because LRA is 48A and it will pull that at startup then drop down to 14.7.
hmspe
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- Temple, TX
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I think the Trane data is in error. Their product data publication 22-1940-1C-EN dated 31 Mar 2020 uses 12.4 for the RLA for 3 ton, 4 ton, and 5 ton units. It would be highly unusual for 3 ton, 4 ton, and 5 ton units to have the same compressor RLA. There is a note in the electrical table in publication 22-1940-1C-EN that says in part for thecompressor RLA, "The value shown is the branch circuit selection current."
A 12.4 RLA for a 5 ton unit doesn't pass the smell test. I don't think the laws of physics have changed, and no matter how many operating steps a variable speed unit has I don't think you can get 5 tons of cooling with a compressor motor that's about 2 HP based on the RLA. Trane's 4TTV8X series is 12.4 compressor RLA for 3 ton, 16.0 RLA for 4 ton, and 19.3 for 5 ton. The 5 ton 4TTV8X has an MCA of 27.0. The compressor in a Daikin DZ17VSA601B is 29.0 RLA.
I don't trust Trane's numbers. To stay on the conservative side I would use ((36.1 - 2.3) X 0.80) = 27.0 for the compressor RLA and 29.3 amps as the running load for the unit.
A 12.4 RLA for a 5 ton unit doesn't pass the smell test. I don't think the laws of physics have changed, and no matter how many operating steps a variable speed unit has I don't think you can get 5 tons of cooling with a compressor motor that's about 2 HP based on the RLA. Trane's 4TTV8X series is 12.4 compressor RLA for 3 ton, 16.0 RLA for 4 ton, and 19.3 for 5 ton. The 5 ton 4TTV8X has an MCA of 27.0. The compressor in a Daikin DZ17VSA601B is 29.0 RLA.
I don't trust Trane's numbers. To stay on the conservative side I would use ((36.1 - 2.3) X 0.80) = 27.0 for the compressor RLA and 29.3 amps as the running load for the unit.
That very well could be, but that would be a huge issue for Trane and whatever listing agency listed the product to correct. I emailed their tech support and ask that they confirm the FLA and RLA numbers and they did.
If the FLA and or RLA were wrong I would expect a product recall of the nameplates and them to issue new nameplates to all units with the incorrect ones.
Not saying Trane is correct but I took steps to notify their tech support, explaind its for a service load calculation and they confirmed the numbers and confirmed that's what they intend the published RLA and FLA are for, load calcs.
kwired
Electron manager
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- NE Nebraska
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They all do that, in proportion to RLA. Most usually end up with MOCP of around 2 to 2.5 times the RLA, but MCA is still only 125% of RLA plus other loads.
wwhitney
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- Berkeley, CA
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You must have gotten a poorly informed technical support worker. A little more research shows that the Trane XV19 line of units are inverter driven. I'm unclear on the rules for nameplate labeling on inverter driven HVAC units. But the product line spec sheet at https://trane.com/WEBCACHE/22-1940-1D-EN_10122021.PDF shows that the line includes 2, 3, 4, and 5 ton units. The correspond nameplate data are:
Tonnage / MCA / MOCP / RLA / LRA / FLA (fan)
2 / 19.1 / 25 / 8.5 / 48.9 / 2.3
3 / 26.9 / 30 / 12.4 / 48.9 / 2.3
4 / 31.8 / 35 / 12.4 / 48.9 / 2.3
5 / 36.1 / 40 / 12.4 / 48.9 / 2.3
Note that the compressor LRA is the same for all the units, even though a different product FAQ on the Trane XV19 line that I found indicates that the larger units use larger compressors.
More important for your service load calculation is that the 3, 4, and 5 ton units have the same RLA of 12.4 and Fan FLA of 2.3, while the MCA and MOCP is increasing with tonnage. This demonstrates that just using RLA and FLA is insufficient to describe the load. And it is frustrating that the nameplate does not have sufficient information to allow the end user to duplicate the MCA and MOCP calculations--any such attempt based only on RLA / LRA / FLA would give identical results for the 3, 4, and 5 ton units.
The only conservative choice for "nameplate rating" for this unit is MCA.
Cheers, Wayne
Article 220 only requires 100% load, that is by my understanding RLA and FLA, I don't see anything in article 220 would mandate using an MCA in a article 220 load calculation other than for a branch circuit,
Certainly we cant be expected to reverse engineer a MCA but if I have missed something in the code mandating the use of a MCA for a dwelling unit calc like 220.83 I'd like to know.
I have to justify my calc numbers, if I get doubtful and over shoot 10 or 15 units now I am possibly off by hundreds of amps and oversizing a transformer that could be considered an 'engineering error or omission' or loose my job. If the manufacture lies on their nameplate, or faked a UL listing I can't be liable for that, I am not even the HVAC contractor supplying the equipment.
I just happened to notice it, and thought it was odd, I bet a there are thousands of services sized off Trane RLA / FLA numbers.
Trane is a such huge well known company, but any manufacturer of UL listed equipment well known or not should have two fail safes to able to get the RLA / FLA nameplate correct per their intended meaning in UL 1995 and now UL/IEC 60335-2-40.
First if there is an error their internal QC engineering team should catch it,
failing that UL or ETL whomever is listing it should catch it.
(It should be easier than ever since they only need to make one nameplate now for the entire global market.)
If both fail to catch it my call to the even the greenist tech support worker on their first day of working the phones live should catch it as all they did was ping someone on their engineering team like so;
'Hey Aice this customer is asking if the FLA and RLA are correct and if Trane recommends using that on NEC load calculation ....'
Alice in engineering glances at a file and confirms its correct.
-> If the nameplate seems off or is incorrect Alice will check in with her team leader Bob and begin the meeting process to issue a product recall, I'd imagine all the dealers would need to apply new nameplates.
Now that I got my answer I did ask the tech support an additional question:
How did Trane came up with that MCA / MOP number from the RLA /FLA?
and the tech support person was trained well enough to keep people like me from wasting Alice's time and deflected me saying I should contact my local dealer.
It would be nice if they could give me some reassurance of what they used to get the different MCA /MOP with the same RLA / FLA.
In Article 430 there are all types of duty cycle for motors, perhaps it has to do with that ? Or the units run at a higher pressure so the LRA is higher, I have no idea.
wwhitney
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- Berkeley, CA
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OK, but the data available to you clearly indicates that RLA + FLA is not 100% of the load.
Cheers, Wayne
wwhitney
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- Berkeley, CA
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- Retired
To expand on that (my edit time expired):
I guess since 220.82 refers to the "the nameplate rating(s) of the heat pump" it is reasonable to say that the plural option is there to allow you to add the RLA and FLA and any other individual loads listed, rather than just using the MCA. I would say that if it said "the nameplate rating of the heat pump," the MCA is the only load rating on the nameplate that applies to the entire piece of equipment.
However, see post #8. You have enough data available to conclude the nameplate is wrong. An RLA of 12.4A is just not plausible for a 5 ton unit.
Cheers, Wayne
To me its clear thats point of putting the Full Load Amps (FLA), HP, and Run Load Amps (RLA) for fan motors and compressor motors on a nameplate for a Article 220 calculation. I could see it being a trick question on a exam, 'whats the minimum calculated load when the nameplate says...'
UL 60335-2-40 requires it to be marked correctly and describes how to do it including a variable speed drive compressor but I am no expert on refrigerant compressor motors. Perhaps its like my '20HP shop vac' the UL sticker says it draws 5A at 120V, or a 2HP garbage disposal that only draws 4 amps... marketing fluff?
Hopefully someone else on here is a Trane dealer and will pursue UL or Trane to figure out whats going on. Should they not recall the units if they have a inaccurate UL nameplate? who knows what else is faulty or fake if the nameplate is?
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wwhitney
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Certainly for Article 220 Part III. For 220.82 it's not quite as clear.
Great, but now you are presented with a nameplate where it is pretty clear it is not marked correctly. So you need to determine how to proceed with your calculation in this unusual case. I strongly advise against using "12.4 + 2.3", that is significantly non-conservative.
Cheers, Wayne
The name plate matches the data sheet you found on their website so if the nameplate was incorrect I'd expect a mismatch, also the manufacture said the numbers are correct.
https://www.trane.com/WEBCACHE/22-1940-1D-EN_10122021.PDF
I was also using 228.83, my understanding from UL 1995 (which is admittedly out of date) is FLA and RLA are the appropriate numbers used in calculations.
This is from a very old copy of UL 1995 (1999):
If the nameplate is wrong on something I dont think you'd go ahead and accept it and try to guess what the correct value is? You'd reject the equipment as who knows what else is defective and its a expensive unit.
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wwhitney
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- Berkeley, CA
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Not necessarily, that would be obvious to anyone who cross checks. But if both the spec sheet and the nameplate are wrong (e.g. the numbers on the spec sheet were developed during the design, but with typos, and then production takes those numbers to make the nameplate), that's not quite as obvious.
On the face of it, the pattern of RLA data in that spec sheet is not consistent with physics. Also, the pattern of RLA and FLA data is not consistent with the pattern of the MCA data.
Well, if the nameplate only had RLA and FLA on it, I agree you'd be stuck. But it also has MCA and MOCP, which do follow a plausible pattern. And for branch circuit sizing, those are the important numbers, so the ones that likely got a bit more attention paid to them. So given that, it is reasonable to still trust those numbers (or at least trust them more than the RLA).
I don't think a typo on a nameplate impugns the entire product, likely nothing else is wrong with and it works fine.
Cheers, Wayne
It wont pass inspection and would be a serious UL violation, plus I dont know what numbers are correct perhaps the MCA and MOP are wrong then?
I have had inspectors reject equipment with a faulty nameplate several times, recently we had to acquire two new nameplates.
I agree
How do you know there aren't other things in that compressor unit that aren't drawing power, like controls? This is similar to air handlers where there is a big fan and a control power supply. The nameplate may list a FLA for the fan motor, but there is something else that sums up everything. Typically, the air handler provides the power for the contactor in an air conditioner, so the AC unit may have no local control power. But if it has a VFD, there could be a control section powered from the AC compressor supply sircuit.
To me, the safest thing to do is to use the MCA and subtract 25% of the RLA from that to get the full load. Same thing for an air handler if you have multiples and need to get rid of the 25% add on factor for a largest motor except subtract 25% of the FLA from the nameplate total.
To me, the safest thing to do is to use the MCA and subtract 25% of the RLA from that to get the full load. Same thing for an air handler if you have multiples and need to get rid of the 25% add on factor for a largest motor except subtract 25% of the FLA from the nameplate total.