Guidelines on Load Diversity
Guidelines on Load Diversity
(OP)
I am trying to find guidelines the electrical community has concerning load diversity. The aim is to try and determine the appropriate service capacity size for an expansion at a clients facility, the expansion will have a certain level of connected load. We feel the site electrical engineer is being overly conservative by using 100% diversity, and we'd like a basis for a counterargument.






RE: Guidelines on Load Diversity
The IEEE Grey Book and perhaps the Red Book talk about diversity, but only provide general guidelines.
Electric utilties have learned through experience diversity factors that can be applied to residential and commercial loads.
But industrial loads are difficult to generalize. There are facilities where pretty much everything runs balls out all the time. In others, there is a lot of spare equipment and significant diversity.
The best approach is to get utility billing data and check out the peak demand for the past year. Compare this with the connected load and you'll get an idea on the diversity, after you allow for appropriate demand factors.
RE: Guidelines on Load Diversity
In a limited since, the apparent oversize this causes is a safety factor. When you recognize some mechanical and structural codes require safety factors of 5, 10, 20 and occasionally more you realize we electrical folks actually get off fairly easy.
I co-authored a paper on reliability that will be published in a forthcoming IEEE Transactions. With regard to overall reliability, "oversizing" (underloading) is the simplest and most cost effective method to achieve reliability for simple systems. (We refer to it as "Simple-Robust.") It's a big enhancement for complex systems too. This is based on about a half-dozen FMEA (Failure Mode and Effects Analysis) studies we conducted over the last 6 years on several refineries including two of the largest in the world. We didn't deal directly with safety issues in the paper, but it enhances that too.
From the 2002 National Electrical Code
I don’t do residential.
I’ve taken Article 220 and deleted all “dwelling” sections - as indicated by an ellipsis (…). In some of the remaining subsections I retained only the title and left the review of the content as an exercise for the student. I retained the critical cross-references to external Sections that effect industrial / commercial design and the key “basic” rules within the Article.
I draw particular attention to 220.10. Since I have also left the references to “… applicable demand factors permitted by Parts II, III, or IV…” (220.14 and 220.21) how would you size the equipment under question? Cite your Code references.
Remember: "noncoincident loads" are generally mutually exclusive such as electric space heating and air conditioning or "running" and "spares." They are not "probabilities."
RE: Guidelines on Load Diversity
RE: Guidelines on Load Diversity
It's pretty common to size distribution equipment based on connected load - loads tend to grow with time and the excess capacity often saves a lot of time and effort (and downtime) later on.
You will often see the facility's service conductors meeting utility incoming conductors about half their size.
RE: Guidelines on Load Diversity