New assumed Current Demand of Installation

[Sparky12021986]

OMG!! can somebody please point me in the right direction because i am sure that i am looking in the wrong section of the REGS book... here is my question...

Explain with reasons the New Assumed Current Demand of the Installation?

My answer is this...

For economic and reliable design, the maximum demand of an installation shall be assessed. In determining the maximum demand of an installation or part thereof, diversity may be taken into account.

Taken word for word out of 311 of the REGS book.. I am pretty sure that, that still has not answered my question can anybody shed some light on this subject thanks....

 

[telectrix]

take 100% of the largest load ( usually shower, no diversity), then 40% of the rest added together.

 

[johnboy6083]

when i was revising or the 2391-2, i could not find an exact reference to that term in any of the books or regs i have.. It was part of a past exam, that i revised from. The other lads i took the course with, couldnt find it either.

 

[Richard Burns]

Have a look at appendix 1 in the on site guide for details on maximum demand and diversity calculations.

Tel's suggestion gives a more realistic figure to use, but if this is an exam question then you may need to justify more.

 

[Sparky12021986]

thanks lads lets see what i can come up with now...

 

[johnboy6083]

take 100% of the largest load ( usually shower, no diversity), then 40% of the rest added together.

what Tel has referred to here is explained more precisely on page 29, 30 and 31 of the electricians design guide. Its well worth getting, if you would like to understand more about electrical design.

 

[Sparky12021986]

what Tel has referred to here is explained more precisely on page 29, 30 and 31 of the electricians design guide. Its well worth getting, if you would like to understand more about electrical design.

How much is that book and where can i get it from do you have a site that i can visit...

 

[johnboy6083]

its roughly £15-£20 and can be bought on the IEE website. I would wait a little while, as a new edition is out soon. Or so ive heard.

 

[Octopus]

The biggest problem with the "total load" is the fact that CU's generally have more breakers than before so the calculations often through up higher loads than are realistic.

I start off by adding them all together and multiplying by 0.4 and see how it looks compared to the home.

EG I viewed a CU replacement job yesterday. The small bungalow has 3 x 30A fuses, 7 x 15A fuses and 2 x 5A fuses which by my ready reakoning gives a total of 205A - and 40% would suggest 80A.

They haven't got an electric shower, nor an electric cooker so I'd hazzard a guess at a total load of no more than 30A

 

[johnboy6083]

the key word is load. An MCB ect is often selected to protect the cable, not always the load. This means that often an MCB rating has no bearing on the current being pulled. The method Tel used with the MCB's is simple, and doesnt require counting the appliances ect. Max demand and diversity calcs are tarted up guesswork most of the time anyway.