Help! Calculation maximum demand and diversity for 2396 project.

[Groot2024]

Hi All,

This is my first time posting although I have been watching from afar for years. I am a fully qualified electrician working in the industrial sector in the UK.

I completed my City and Guilds 2396 exam with a pass approximately 2 years ago but have been putting off the project since. I could make excuses but the fact of the matter is, I have never found the motivation to start, until recently!!

I really wish I competed the project sooner as all the information I gained on the course has left me.

I’m confused and probably over thinking a lot but I hope someone on here can help me please.

When calculating a 3 phase sub main cable suppling a DB containing both power and lighting single phase circuits, where do you start??

I have calculated max demand for each individual circuit but how do I relate this to the sub main supply.
Would I calculate the load for each phase?

I would also group multiple socket circuits and apply diversity to them but not sure how this works when calculating the load on each phase?

I know how to calculate the max demand and size the cable appropriately for a single 3 phase circuit and I am also aware of multiplying VD from sub main and final circuit but can’t seem to get my head around the max demand of an entire DB with single phase circuits when applying diversity.

I’m sure it’s obvious

Many thanks in advance,

Stuck!!!

 

[Tom256]

Going into the kingdom of the dart arts here hence the need to show an understanding of the loads, usage and special consideration such as future demand for the installation. The designer will need to show an understanding of the demand for the installlation and even then it can never be said to be an exact science.

As such set out the loads, time demands each day and usage, an installation outline will help.
With no specifics in mind by way of a starting point to jog memory the demand on a Sub-Distribution board can be assessed by total installed load (Pmax) (Pdb) x demand factor summed. Tables for demand factor are widely available both for complete installations amd individual sub-boards with mixed loads.
The base calculatiuonis PDB = P1g1 + P2g2 ….. Pngn

P - being loads under continuous duty cycle
g - being demand factor for the load for the type of installation

Pngn = sum of individual types of loads eg, lighting , can also be used

With loads assessed how they are to be allocated to each phase can be set out using a simple spreadsheet