Mastering Diversity

[Hobsoni]

From what I can gather, there are two types of diversity application that stand out to me.

1) diversity based on the load type (street lighting = 1 and sockets = 0.6 for example)
2) what I call 'probability' if we have 10 socket circuits fed from a DB then we apply a diversity to the collective 10 circuits. Ie, what are the chances all 10 circuits being under full load (or perhaps their diversified load) all at once.

But, when we get into larger scaled installations........are there any hard and fast rules for engineers to apply diversity? I know we have a small section in OSG's, but is there a so called immovable point of reference to go to for applying diversity? Or does it purely come from an engineer's experience?

Before anyone asks, no I am not intending to design and install something of this magnitude. I'm just curious to find out, as I have seen some different designs where the diversity is more 'aggressive' than others.

looking forward to some positive responses

thanks

 

[Guest111]

Diversity can vary vastly depending on the situation,I've seen paperwork from a DNO for example and when they work out their cable sizes for feeding a street of houses they base their figures on something like 4KW if the houses have gas available and 5KW if they don't.

 

[D Skelton]

In short no, there aren't any hard and fast rules. It is up to the designer to use their judgement to decide. As Phil said above, the DNOs use only a few kW for each domestic supply because experience will tell them that at any one time no domestic property is likely to be pulling more than 10 or 15A despite it saying 60A on a newly rewired one down that street.

When I'm designing I like to use the expected load of each circuit as much as possible but when designing it is mainly commercial premesis where there is little room for 'probability' diversity as you like to call it.

In a domestic, it is quite easy to say that it is unlikely that the cooker circuit, upstairs ring final circuit and the shower circuit will be on at the same time. In a small factory unit however, I've already calculated the number of computers running off a socket circuit in the office and I've already calculated the load on each tool or piece of machinery. All of which is likely to be on at the same time, from 8am till 5pm that is. The difference being that I'm not using a percentage of the first socket circuit and a percentage of the rest, and then some decimal multiplier for the items of machinery. I'm using actual calculated loads. The domestic might call for you to use 32A on the first socket circuit and then 16A on the next, but if you know that the most those socket circuits are going to pull combined is 7.5A, use that instead of the numbers plucked out of thin air in a guide somewhere.

I wouldn'd say demand and diversity is some dark art, I'd just say it comes down to the common sense and experience of the designer.

 

[gazj82]

I would go with all the D Skelton has said, but would just add, that there are no hard and fast rules because everything other than domestic would wildly differ depending on the building use. I.e I look after some units for a customer they are identical units (as far as floor space goes), one is used by a steel work fabricator one is used purely for storage, all the other units would be somewhere between those two extremes.

I have done buildings tha have cooling enabled by a chiller, with dx units as backup. This creates a situation where big diversity will occur as we know there will never be a condition where both could run together.

So as D Skelton said, no hard and fast rules, every installation is different and with practice you eventually get pretty good at knowing how to apply diversity.

 

[Knobhead]

If you want to take what Phil said about the DNO’s a step further. The grid supply system works on 2KW per supply including light industrial. Bulk supplies fall in to their own category.

Two of the places I’ve worked the loads were cyclic. One the load dropped by 60% at the weekend, another the load went up by 25%.