Not disputing the rationale or probability of coincident load that justifies the use of demand factors. I just don't understand how you can comply with 220.40 by applying a demand factor when applying a demand factor to the feeder/service calculated load will produce a result smaller than of the loads on the branch circuits.
So how does this comply with 220.40?
220.40 states that the calculated load for the feeder can't be less than.... after the demand factor is apply. 220.40 is saying to use the demand factor and then the feeder can't be less than that calculated load
Im sorry but I am having a hard time comprehending this. Any way you could use an example to demonstrate what is being said?
220.40 is the first section of Part III, Feeder and Service Load Calculations. So it is just explaining the general strategy for those calculations: take the loads of the branch circuits supplied; apply the demand factors permitted; and the result is the load on the feeder or service.
I'm sure it's a simple concept, I believe I am having an issue with the way its worded.
That last part does throw me off a bit. Maybe answering this would help... What is the difference between "calculated load" and "sum of the loads"?
It just seems bizarre to me. Why not just say:
"Calculation" is a broader term than "summation". Calculations include summation (adding up the loads), multiplication (applying a demand factor) and even taking square-roots (√3). That's why that little gadget is called a calculator and not just an adder-upper. First you sum the branch circuits (add up), then you calculate the feeder load (multiply by demand)
The jargon of NFPA-70 may act as a barrier to entry, without a Rosetta Stone of practicing experience, to translate when inspectors' creative license is wrong.
I believe the goal is to create disputes settled only by expert builders, senior planners, and teams of engineers.
Check out D1 - D10 in annex D
Perhaps this will help you xptpcrewx. Look at the reason this is in there. We want to make sure that the wires can carry the load (amperage) that is going to be applied to them without overheating and burning up, period. So the bottom line is the ampacity of the conductors isn't allowed to be less than the actual amperage of the circuit (technically with a fudge factor). It is determined that one can safely reduce the "calculated maximum amperage" on the wires by anticipating nonconcurrent loads of many different items. So we are allowed to calculate the load by adding up all of the items and then reducing that load by applying demand factors, a s others said, because not all stoves are going to have all burners on at the same time, even if 80% of the people are cooking, each burner cycles on and off irregularly and with 100 burners total, 80 of them being used, half of them cycling 50% of the time, half cycling 75% of the time, they will not all be on at the same time. Hence demand.