how to calculate the size of cable from one DB to another DB

[submariner111]

I am currently studying the 2357 qual and have got a little stumped on a question about the size of cable between 2 DB's.
What i am stuck on, is that i am not sure if the cable is sized using the size of mcb used for each of the circuits at the new DB, or whether its done by the rating of each of the sockets i.e 0.5A per socket.

Any advice on this would be greatly appreciated.

 

[ezzzekiel]

it will need to carry total load after diversity

 

[submariner111]

sorry to sound stupid here, but i a learning, but do you mean the total load of the sockets etc, i.e 0.5A + 0.5A=1A then apply diversity to the total?

 

[Richard Burns]

The cable should be sized so that it has suitable current carrying capacity to handle the expected load from the new DB.
if you have a look at the OSG this gives you approved methods of calculating diversity for various different loads.

A socket outlet does not have a demand of 0.5A unless it is a 2A socket outlet, for 13A socket outlet circuits the demand is 100% of largest point of use plus 70% of the remaining points (assuming this is an office environment).

You can either calculate the diversity as a whole installation of by adding up the total of the diversified load for each point of utilisation (do NOT apply diversity again), however this last will give an unrealistically high value.