NEC calculation for Large number of AC units

[liqababy]

Hi,

So I had a question about a huge hospital design i once saw. How does the NEC handle installations like that where there are a large amount of equipment and AC units that if considered to all be taken at full load they would result in a service size that is ridiculously large? Considering that like the MRI machines won't be on all at the same time or 24/7, or VRF AC units may not be on all at the same time at maximum use, or exhaust fans and other medical equipment won't all be on at the same time. Something of that scale would end up with some crazy service size that may never be used.

are there calculations or provisions aside from the receptacle load demand factor than can be applied? or how does someone go about even doing that caluclation without leading them to require a small substation?

 

[tortuga]

One thing I do is calculate the real load of the AC units and not just use the Minimum circuit Ampacit , it can be a bit tedious as the manufacturers dont always give you a totaled up Running Load Amps (RLA) they supply a list of numbers like RLA for the comressor and Full Load Amps (FLA) for the fan motors etc.

 

[don_resqcapt19]

One thing I do is calculate the real load of the AC units and not just use the Minimum circuit Ampacit , it can be a bit tedious as the manufacturers dont always give you a totaled up Running Load Amps (RLA) they supply a list of numbers like RLA for the comressor and Full Load Amps (FLA) for the fan motors etc.

That make sense, but a 2023 code change says:

220.50(B) Air-Conditioning Equipment.
The conductor sizing requirements specified in Part IV of Article 440 shall be used to determine air-conditioning loads for hermetic refrigerant motor-compressors.

The conductor sizing rule in 440.33 is pretty much the same as the calculation required for the minimum circuit ampacity number on the nameplate.

 

[Birken Vogt]

The conductor sizing rule in 440.33 is pretty much the same as the calculation required for the minimum circuit ampacity number on the nameplate.

What was the rationale behind that change? That means that the 25% largest motor factor is getting added in over and over again.