Calculating maximum demand

[pumpkinbreath]

Hi again

I also have a query about determining the installations maximum demand for when an electrical installation certificate must be filled in. I have calculated the demand for my test scenario using Appendix 1 of the On Site Guide as 103.92A using the breaker values. However I have seen post on this forum that it can be calculated by adding the sum of the breakers and then multiplying this figure by 0.4, is this a recognised method? I used it and got 43.2A, a big difference no?

I don't have the actual readings for the circuits in Amps or Watts, only breaker values as it is a practical exam.

Any suggestions...

 

[Engineer54]

Not just one post, have you seen this calculation i think!!! That's because it's been used by electricians and engineers alike for many many years now. ...Maybe because it gives a much closer/realistic figure than using the BRB/OSG!!!

When was the last time you see 104A flowing in a domestic installation??? lol!!!

 

[topquark]

Yes, that's a common way of estimating. Bear in mind that the breaker is only there to protect the cable, it is not a statement of how much current the circuit will draw in use. In practical terms the current requirement should come no where near that maximum. The exception being some, arguably poorly installed, showers. Have a read up on diversity in the BRB.

 

[SirKit Breaker]

Hi again

I also have a query about determining the installations maximum demand for when an electrical installation certificate must be filled in. I have calculated the demand for my test scenario using Appendix 1 of the On Site Guide as 103.92A using the breaker values. However I have seen post on this forum that it can be calculated by adding the sum of the breakers and then multiplying this figure by 0.4, is this a recognised method? I used it and got 43.2A, a big difference no?

I don't have the actual readings for the circuits in Amps or Watts, only breaker values as it is a practical exam.

Any suggestions...

Thats the method I have used for years. There are 3 reasons behind this. 1, I dont like maths. 2, It is easy, and 3, no one has ever questioned it.

Cheers.........Howard

 

[ian]

I use the following method. Take the largest breaker thenadd 40% of the remaining breakers to it.

I have put this on every eic I have filled in for years, I havebeen questioned a couple of times by the elecsa assessor and he has never had aproblem. Look at table 1B of the OSG (9) it makes it clear in that.

Ian

 

[londonlec]

I recently calculated it long hand, for each circuit, then added them together.
Then turned the page in the book and found the x 0.8 method!

I must admit, I have recently been educated to not just put 60/80/100 amps (suppliers fuse).

 

[TPES]

Add up all the breakers in the consumer unit except the largest size breaker...

Multiply this figure by 0.4

Then add onto this figure the size of the largest breaker you left out...

Example..

2 x 6a
3 x 32a
1 x 20a
1 x 16a
1 x 40a

Add all up except the 40a.. = 144 amps Multiply by 0.4 = 57.6 amps then add on the 40a giving you 97.6 amps

This is the method I was always shown, other people have different variations.

 

[zafer]

Can I ask where did you get the x8 method? which book is that? I like to get that book. thanks