"Diversity Factor" in IEC 60204-1

[Tip DS]

I'm trying to find a way to make the term "diversity factor" a little less ambiguous. Does anyone have a source that clearly defines the term and clearly identifies how it can be determined?

In IEC 60204-1, it requires the following:
5.3 Supply disconnecting (isolating) device
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5.3.3 Requirements
Where the supply disconnecting device is one of the types specified in 5.3.2 a) to d) it shall fulfil all of the following requirements:
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-have a breaking capacity sufficient to interrupt the current of the largest motor when stalled together with the sum of the normal running currents of all other motors and other loads. The calculated breaking capacity may be reduced by the use of a proven diversity factor. Where motor(s) are supplied by converter(s) or similar devices, the calculation should take into account the possible effect on the required breaking capacity.

The term "diversity factor" is not defined in this document. I have some idea of what they mean, but it would be nice to get a definition, and a method for determining a "proven diversity factor".

 

[charlie b]

My source is the Internet, but it matches what I remember from a college textbook. This is the official way to calculate diversity factor, though it might not be the same concept that is intended by your IEC citation. So I can't say this will answer your question.

Consider a facility that has four large switcboards. Look at their loads over, let us say, a week's time.

• Swbd 1 sees a peak demand of 400 KVA, and that generally occurs at 10am.
• Swbd 2 sees a peak demand of 300 KVA, and that generally occurs around noon.
• Swbd 3 sees a peak demand of 500 KVA, and that generally occurs early afternoon.
• Swbd 4 sees a peak demand of 600 KVA, and that generally occurs late afternoon.
• The sum of these individual peak demands is 1800 KVA.

But since these individual peak demands don't occur at the same time, the maximum load seem at the facility will be less than 1800 KVA. Let's say the peak demand over that week was 1300 KVA.

The "Diversity Factor" is calculated as 1800 divided by 1300, or about 1.4. If you get a result less than 1.0, you made a math mistake.

In your question, you could treat each motor in the same way I treated the 4 switchboards. If you have data that include the peak load drawn by each motor and the peak demand of the set of all motors, you could calculate a diversity factor and treat it as haven been "proven" (i.e., by measurement and calculation).

 

[don_resqcapt19]

The ampacity adjustment table in Annex B, Table B.2(11) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable with Load Diversity, was originally in Article 310 along with what is now Table 310.15(C)(1) (2023 code). It was moved to the Annex because they could not come with with a suitable definition for "diversity" as the table in the Annex is based on a 50% diversity.

 

[charlie b]

To Don's point, I will add that that Annex does not use the two-word phrase, "diversity factor." Instead it uses, "load diversity." I don't believe that phrase is defined anywhere in the electrical engineering world.

Also, if switchboards 1 and 2 in my earlier post ran at 400 KVA each from midnight to noon, and were turned off the other 12 hours, and if switchboards 3 and 4 ran at 400 KVA each from noon to midnight, and were turned off the other 12 hours, it would result in a diversity factor of 50%. My point is that it is not easy to imagine an operational situation that can result in a 50% diversity factor.

 

[Tip DS]

I appreciate the replies on this topic. From everything I've read, I am inclined to agree the consensus leans toward diversity factor being a number ≥1. It seems many people take it to mean the connected load divided by the operating load. (using ampacity or power) In essence, the inverse of the load factor. I suppose a part of my question/concern is, how does the denominator get defined during the design phase? For example, in Naval ship design, load factors are assigned a sort of rule-of-thumb value in Appendix A of DDS 310, which can be adjusted with an understanding of the ship's concept of operation, or special knowledge of the particulars of one of the systems being assigned the factor. So, in the case of Naval electrical system design, I would consider the DDS 310 a "proven load factor" for EPLA calculations. What constitutes a "proven diversity factor" as mentioned in IEC 60204-1? (My assumption is the standard hasn't reached a level of maturity where all these details have been settled. ?)