220.82(C) 100% of the nameplate rating

[wwhitney]

How do you know there aren't other things in that compressor unit that aren't drawing power, like controls?

Hmm, another possibility is that like mini-splits, this outdoor unit provides power to the indoor unit (didn't check installation manual to see if that's true), and that the difference between the 3, 4, and 5 ton units is purely within the indoor unit, they do actually use the same compressor RLA. That would surprise me somewhat, but I can't say that I know enough to say that it's not plausible.

This possibility just reinforces the idea that the load needs to be based on MCA, as that total would include any other loads that are not enumerated as motors within the outdoor unit. So then use MCA or more accurately and still conservatively MCA - 25% RLA (on the assumption that the compressor is the largest motor; if the assumption is wrong, it's just somewhat an overestimate).

Cheers, Wayne

 

[tortuga]

Thanks for the feedback, yeah to be safe I ran the calc with the MCA. But the question remains as these are common units and the next one might be closer to the line.

How do you know there aren't other things in that compressor unit that aren't drawing power, like controls?

I asked the manufacturer to confirm the RLA / FLA on the nameplate were correct and suitable for a load calculation, and they said yes.
I also asked if there was a heater load that was optional or missed and they say no.

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.

My limited understanding both the UL standards requires all the loads to be marked on the nameplate, it addresses VFD compressors explicitly so it seems like the manufacturer should get that correct on their published RLA of the compressor and if a mistake is made they should update people and issue a new nameplate.

 

[mtnelect]

Thanks for the feedback, yeah to be safe I ran the calc with the MCA. But the question remains as these are common units and the next one might be closer to the line.

I asked the manufacturer to confirm the RLA / FLA on the nameplate were correct and suitable for a load calculation, and they said yes.
I also asked if there was a heater load that was optional or missed and they say no.

My limited understanding both the UL standards requires all the loads to be marked on the nameplate, it addresses VFD compressors explicitly so it seems like the manufacturer should get that correct on their published RLA of the compressor and if a mistake is made they should update people and issue a new nameplate.

Remember in HVAC the compressors are "Hermetic" and cooled by the refrigerant. The manufactures take that's into consideration when determining the label on the unit. Trying to reconstruct that information is impossible.

 

[tortuga]

Remember in HVAC the compressors are "Hermetic" and cooled by the refrigerant. The manufactures take that's into consideration when determining the label on the unit. Trying to reconstruct that information is impossible.

Thanks Michael do you think the Trane Data sheet in post 11 is correct ?
It shows the same Hermetic compressor 12.4 RLA and the same fan 2.3 for the 3, 4 and 5 ton units.
Is that typical?

Would you use those numbers in a article 220 load calculation for a service?
Does this violate the laws of physics or is it something to do with varying duty of the hermetic compressor and the VFD or the system pressure on startup LRA?
Trane said their numbers are correct and these are energy efficient units, but declined to explain how and why perhaps its proprietary?

It would be interesting here from others with experience in the field amp-metering a sample of these in the 3, 4 and 5 ton range. It would need to be while they are running at full load for 1/2 hour.

 

[mtnelect]

Thanks Michael do you think the Trane Data sheet in post 11 is correct ?
It shows the same Hermetic compressor 12.4 RLA and the same fan 2.3 for the 3, 4 and 5 ton units.
Is that typical?

Would you use those numbers in a article 220 load calculation for a service?
Does this violate the laws of physics or is it something to do with varying duty of the hermetic compressor and the VFD or the system pressure on startup LRA?
Trane said their numbers are correct and these are energy efficient units, but declined to explain how and why perhaps its proprietary?

It would be interesting here from others with experience in the field amp-metering a sample of these in the 3, 4 and 5 ton range. It would need to be while they are running at full load for 1/2 hour.

Before wiring a HVAC (Heating Ventilation Air Conditioning) unit I always read the literature first, see foot note (d).

 

[tortuga]

Before wiring a HVAC (Heating Ventilation Air Conditioning) unit I always read the literature first, see foot note (d).

OK I'd be most interested to know if you have ever ammetered one of these?

I am not wiring anything up or selecting a branch circuit the electrician will do that rather I am doing a Article 220 load calculation that asks for the 100% Full load Amps or Running Load Amps to size a residential service or a feeder & transformer in a office building etc. There may be 15 of these units on a feeder, so using the correct number is important. Others in this thread are suggesting Trane's FLA and RLA numbers are incorrect. UL requires all the load be listed on the namplate correctly they cant just put whatever they want on there and hide behind a note.

 

[mtnelect]

Yes, and the running amps are usually lower, depending on the on the weather conditions. HVAC hermetic condensing units are subjected to harsher conditions than standard motors and constructed too very high tolerances to last 15 to 25 years. I always follow the manufacture's label recommendations and use only the 60-degree collum on Table 310.15(B)(16) and increase the wire size on runs longer than 100 feet.

 

[tortuga]

I always follow the manufacture's label recommendations

Do think that seeing the same RLA on the 3, 4, and 5 ton units is normal? Is it the same compressor and it runs more often on the 4 and 5 ton? If I ammetered a 3 ton and a 5 ton at full load would I get the same reading?

the wire size

I'd like to emphasize we're discussing service load calculations, not discussing wire sizing or breaker sizing, I have had to emphasize this with the Trane tech support people also. Were just discussing the 100% full load amps and running load amps.

 

[wwhitney]

If I ammetered a 3 ton and a 5 ton at full load would I get the same reading?

If that were true, I don't see why the MCA would be higher.

Cheers, Wayne