Monitoring Existing Load for Load Calculations

[philly]

I know that when it comes to determining existing loads for the purposes of load calculations the NEC allows a 30-day monitoring period of these loads in order to determine the existing load.

Is there any guidelines that exist on when this monitoring would not be required? For example lets see we are installing a new 480V 1600A switchboard and from this switchboard we are re-feeding a small stepdown transformer and 120/208V panel. If you know from taking clamp on meter readings from this existing panel that the load is very small compared to your overall new switchboard load is it required to perform the 30 day monitoring, or can an approximation of some sort be made?

Are there some applications like an industrial setting where small panels represent only a fraction of the today load where monitoring may not be required as part of calcs where perhaps in a commercial environment where the panel represented more of the overall load that it would be necessary?

If monitoring is performed are you required to show the entire 30 day monitoring readout or can the largest kVA reading simply be listed in the load calc?

 

[ron]

The largest kVA reading is listed in the load calc.

If the existing load is so small due to the transformer or feeder size that the new SWBD cannot be overloaded, then we don't do a 30 day

 

[philly]

The largest kVA reading is listed in the load calc.

If the existing load is so small due to the transformer or feeder size that the new SWBD cannot be overloaded, then we don't do a 30 day

Would an example of this be a 480V panelbaord that feeds a downstream 120/208V panel through a 45kVA transformer?

For instance if we were doing a load calc at the upstream 480V panelbaord which fed this 45kvA transformer and panel but didn't know the existing load at the downstream 120/208 panel (and didn't monitor is) can you make the assumption of 45kVA in the load calc knowing that this would be the maximum load from this panel and use this in the 480V panel load calcs as long as it didn't effect the load calcs (is very small compared to other loads)

 

[philly]

Also in a case where there are existing panels that either had their total load monitored or estimated do you show a panel schedule for these panels in your schedule drawings if you know the names and sizes of all the branch breakers and put a note in schedule saying how load was determined?