Standard and Optional Methods

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bphgravity

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I have done some research into the history of the NEC providing both a standard and optional method for calculating feeder and service loads. As far as I can see, there is no substantiation for this.

What purpose does it serve to provide optional methods. This appears to me to not meet the scope and intent of the NEC as a minimum safety standard. I think that the minimum required calculation should be provided and if one wishes to increase capacity, then that can be in their design.

I am considering a proposal for removing portions of both the standard and optional calculation and then reforming the section combining the remaining requirements. Before I make the effort, I would like to hear some feedback on how having two methods provides a benefit to the user and allows additional safety. I don't think it does, plus it takes up lots of space and adds to confusion.

Any thoughts? Do you prefer to have two methods to choose from or would you rather see a simplified single method? Any ideas on when and why optional methods came into being?
 
Re: Standard and Optional Methods

I have never had to use the optional method for an actual project design. The types of facilities I most often work on do not have optional methods. However, while studying for my Administrator?s License, for every sample problem I solved, the optional method always gave a lower service load then the standard method.

So I conclude that the optional method is not there to provide a greater allowance for safety. But neither do I believe that using it is a step in an unsafe direction. Rather, it is another , and often simpler, way of looking at the same situation. It just takes away a little bit of the ?overkill? that is built into the overly conservative standard calculation process.

I applaud your taking the initiative on this question. I just don't think there is a problem in need of a solution.
 
Re: Standard and Optional Methods

Originally posted by bphgravity:
"I have done some research into the history" of the NEC providing both a standard and optional method for calculating feeder and service loads."Any ideas on when and why optional methods came into being"?
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:bpgravity,Not being an Instructor myself,just a Student,I'd be more than interested into the history that you have researched Sir.You gotten me sitting up in my chair and leaning forward, my "full attention".
 
Re: Standard and Optional Methods

Originally posted by dillon3c:
...You gotten me sitting up in my chair and leaning forward, my "full attention"...
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Trust me when I say that it is not all that interesting. In the late 1970's and early 1980's, energy conservation became the hot topic and everyone (especially engineers) started looking for ways to reduce energy cunsumption. This extended across all industries from automobiles, HVAC, appliances, and even service sizing requirements.

Engineering data was submitted to the code making panel during the proposal stage that indicated many buildings were having their services overdesigned and that smaller demands were now in place due to other industry factors. For example fluorescent lighting was significntly more efficent by 1981 and thus the requirement for general lighting load for a commercial building was reduced to 3.5 watts per sq.ft. from 5 watts per sq.ft.

After that, a barrage of proposals were submitted with similar studies on other types of occupancies. Some were accepted others were not. Instead of making across the board changes, some proposals were accepted as optional methods. An example would be new restaurants in 1990.

In all cases, it was determined that the standard method no longer established the minimum requirement for safety or adequacy, yet the standard method stays in place. I too agree that there is not necessarily a safety concern having a standard and optional method, but it also wouldn't compromise safety by removing the more conservative of the two, or as I suggest combine the minimum requirements from each.

Significant sections and tables could be eliminated as they really serve no purpose except for being overly complicated. For example, I feel Section 220.55 and its table is a total waste of space and effort. The table and its' notes are absoultely ridiculus. That entire section could disappear and a more simplied demand for cooking equipment can be established. Something similar to as provided in the optional method for multifamily dwellings in section 220.84. Add everything up and apply a demand. No more individual demands for every appliance or portion.

A typical dwelling calculation requires 9 steps. That is a condensed version. I have seen some spreadsheets with as many as 20 steps for a single family home. The optional method only requires about 3, plus it almost always results in a smaller service.

It just bothers me that issues such as voltage drop is treated as a desing issue yet Article 220 is full of design options. This is not consistent and needs to be changed.
 
Re: Standard and Optional Methods

As you have already found out, the optional calculations are based on actual histories provided by various organizations for specific applications. For instance, the organization that represents the restaurants is interested in cutting down on the service sizes because they build so many and the savings would be enormous. They presented test data to show that the services could be reduced without them being undersized. This helped the restaurant industry but did nothing for other commercial establishments.

Generally, the optional calculations are for a specific type of occupancy and not for general use. If you have a building that you are designing a service for and feel like the optional calculations provides too small of a service size, you are not required to use it, it's optional.

To address the idea of blending the standard and optional calculations, how do you do that without additional testing? You can't just arbitrarily mix two different formulas and trust that they will work. It is possible to eliminate the optional methods but you can't eliminate the standard methods since that method generally applies to more types of occupancies.

In my opinion, instead of eliminating the optional calculations, additional ones could be established for special occupancies. This can only be done by using good data like was done for restaurants. Since the load data is available from a lot of different electric utilities located in different areas of the country, the Edison Electric Institute is intimately involved in a lot of the optional calculation in the past and we will continue to be involved in the future. :D
 
Re: Standard and Optional Methods

Originally posted by charlie:
In my opinion, instead of eliminating the optional calculations, additional ones could be established for special occupancies.
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Just what we need more 'special' rules. :D ;) (It is just a joke)

Bob
 
Re: Standard and Optional Methods

I'm not really suggesting we create new formulas. I think we can take the ones we already know work and use them exclusively for each occupancy type specifically.

For example. We know 3 watts per sq.ft. works well for dwellings. That doesn't need to change. But what makes no sense is to apply one demand factor for general lighting, another for fixed applainces, and yet another for cooking equipment. In this case, I feel the standard method could be complelety elminated for dwellings as it has been shown an adequate optional method works and could be used exclusively.

So what I guess I am basically syaing is that I don't want to get rid of the optional method, I think it would be a progressive step to accept the optional method as the new standard method and drop the allowance for an optional method.
 
Re: Standard and Optional Methods

"After seeing Bill's link to "What time is it in Illinois" I must assume that folks from Illinois are used to confusing codes, rules and policys. :D :D
 
Re: Standard and Optional Methods

Originally posted by charlie:
"After seeing Bill's link to "What time is it in Illinois" I must assume that folks from Illinois are used to confusing codes, rules and policys. :eek:

I have to remember to always check my references before posting. :eek:

Bob
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Re: Standard and Optional Methods

Bryan, assume an apartment building with six units, gas ranges, dryers, W/H, and 800 sq. ft of living space. No extras and small AC. How would you calculate their service sizes with the optional method given in 220.84 in the 2005 NEC? In my opinion, the standard method would be required to be used. :D
 
Re: Standard and Optional Methods

Originally posted by charlie:
Bob, that was a bona fide "gotcha". :D
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Yes that was, no amount of typing on my part can change that fact. :D
grinning-smiley-016.gif
 
Re: Standard and Optional Methods

Other than a minor cost adder for bigger wires and panelboards, how does having a bigger service add cost to a typical residential project? It seems to me that it would make sense to have a minimum size of say 100A for all residences regardless of actual load, and that it be increased if required due to actual loads.

Most residences with gas heat, range, dryers, and wh would then be covered under the minimum service size requirements and no calculations would be required at all.
 
Re: Standard and Optional Methods

Bob, my point is that is some cases, some apartments can be served with a 60 ampere service and it would be fine. If this were a large project, it would be a lot of money.

In fact, that is why the home builder association is always against any increase in cost. If you "only" add a little here and a little there, it will soon add up to a lot of money per dwelling unit. If the costs are prohibitive, that will equate to less units sold and a depressed market. By the way, I am not talking about just the electrical portion of the home costs.

In general, I do not like any group that lobbies the panel members. However, I happen to agree with these guys for the most part. :D
 
Re: Standard and Optional Methods

Originally posted by charlie:
..In my opinion, the standard method would be required to be used... :D
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It wouldn't be required to be used, it is again just an option. For your particular example, the standard method works out to be the lesser of two calculated loads, but that is just because of the simulated ranges.

But this proves my point. Two completely different calculations must be performed in order to detemrine which would be the lesser value. This makes no sense. The optional calculation could be made the standard thus eliminated the lighting demand, and possible appliannce demands, and the cooking demand for just one service demand.
 
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