Max Demand

[jamie-spark]

When doing pirs and pirs before consumer unit changes or db,s when calculating the max demand with help from OSG i often find installations max demand well exceeds the cut out fuse. customers dont care what do yous guys do about it

 

[telectrix]

i use a rule of thumb. add up the MCB ratings and divide by 2. or, you could calculate more accurately applying diversity.

 

[IQ Electrical]

Don't forget that as a competent person having knowledge of the working installation, you can use your own methods to calculate a truer reflection of maximum demand.

The written figures and percentages are more suited to design calculations.

 

[Deleted member 26818]

It is often the case that the calculated maximum demand exceeds the rating of the cut out fuse.
Many have been in use without any problems for many years.
To be honest, I can't actually recall ever having a domestic installation where the cut out fuse has blown.
Had it on industrial installations quite a few times, but that can sometimes be down to unbalenced 3 phase supply voltages.

 

[jamie-spark]

We done a pir the other day in a house 60 amp bs88 fuse supplying the following mcb,s 4 x b32 , 1 x b40, 2 x b16 ,4 x b6

 

[IQ Electrical]

We done a pir the other day in a house 60 amp bs88 fuse supplying the following mcb,s 4 x b32 , 1 x b40, 2 x b16 ,4 x b6

There you have it, it's not an exact science and as spinlondon points out, you just don't see a service fuse blown on overload.

 

[SirKit Breaker]

I use the following calculation. add up the rating of all the circuit protective devices, and times the value by 0.4. This is near enough to be acceptable, and is quicker than applying diversity. Done this for years with no problems.

Cheers..........Howard

 

[IQ Electrical]

I use the following calculation. add up the rating of all the circuit protective devices, and times the value by 0.4. This is near enough to be acceptable, and is quicker than applying diversity. Done this for years with no problems.

Cheers..........Howard

I multiply by 0.42 but only on the 3rd Tuesday of a month and never in an Easterly wind

 

[Deleted member 26818]

I multiply by 0.42 but only on the 3rd Tuesday of a month and never in an Easterly wind

I used to use that method, only I could never remember if an easterly wind blew from or towards the East?

 

[telectrix]

i use a factor of 0.5 as the sums are easier.

 

[redface]

We done a pir the other day in a house 60 amp bs88 fuse supplying the following mcb,s 4 x b32 , 1 x b40, 2 x b16 ,4 x b6

the max demand is prob 50 a max if that domestic

 

[IQ Electrical]

the max demand is prob 50 a max if that domestic

Your remote current monitoring system is impressive!

What's the Ze?

 

[telectrix]

Your remote current monitoring system is impressive!

What's the Ze?

(root3 x his iphone charge time) /1000

 

[domestic spark]

add up all MCBS bar the highest rated one. x answer by 0.4 then add largest MCB to that figure. DONE.