max demand

[minivanman]

Hi All,
Just looked at a job and the max demand comes out at about 100A, main fuse is 60 A, they want a new cooker circuit installed (old gas cooker already removed for new electric and want the cooker back on ASAP as got loadsa kids), cooker demand after diversity is 20A taking the calculated max demand to 120A.

Would you just do the addition and advise an upgrade on the cert or tell the customer that they need an upgrade of the fuse prior to the work?

Do DNO charge for fuse upgrade?

 

[andekoch]

just had the dno in to put in a new fuse for a flat we are refurbishing (splittign the existig building into 2).
They asked for the maximum demand (which was around 110A, based on the OSG max demand calcs, elec cooker but no elec shower) and they said we could have a 60A supply.

In reality this will probably be ok but it does sort of make you question the max demand calcs.

You may have to take a view on what the real demand is as opposed to what the calcs say. Try a clamp meter on the tails to see what they are really drawing at a typical loaded time. Also it is worth telling the customer that the demand calcs say they need to upgrade the fuse (but the dno will probably not do it, and I am sure the ywould charge for the privelage of upgrading).

 

[SirKit Breaker]

Maximum demand calculation that i use is the following.

Add up the total current of all the mcb ratings in use, apply diversity as required and multiply your figure by 0.4

I.E

6a lighting circuit
32a ring
32a ring
16a radial
45a shower

= 131a x 0.4= 52.4a

Regards..........Howard

 

[old dog]

Maximum demand calculation that i use is the following.

Add up the total current of all the mcb ratings in use, apply diversity as required and multiply your figure by 0.4

I.E

6a lighting circuit
32a ring
32a ring
16a radial
45a shower

= 131a x 0.4= 52.4a

Regards..........Howard

that is a very old rule of thumb way of calculating max demand and nine times out of ten it is spot on

 

[David.]

Maximum demand calculation that i use is the following.

Add up the total current of all the mcb ratings in use, apply diversity as required and multiply your figure by 0.4

I.E

6a lighting circuit
32a ring
32a ring
16a radial
45a shower

= 131a x 0.4= 52.4a

Regards..........Howard

hey mate,

i find this a great way to calculate but i was just wondering you say to "apply diversity as required" but in your final answer it seems no diversity applied?? Just straight add and divide (which does seem loads easier )

cheers

 

[ANT68]

hey mate,

i find this a great way to calculate but i was just wondering you say to "apply diversity as required" but in your final answer it seems no diversity applied?? Just straight add and divide (which does seem loads easier )

cheers

Pardon my ignorance, where does the 0.4 come from??

Maximum demand calculation that i use is the following.

Add up the total current of all the mcb ratings in use, apply diversity as required and multiply your figure by 0.4

I.E

6a lighting circuit
32a ring
32a ring
16a radial
45a shower

= 131a x 0.4= 52.4a

Regards..........Howard

pardon my ignorance,where does the 0.4 come from

 

[SirKit Breaker]

Ant68, see the comment at the foot of OLD DOGs post.

Its just one of those things picked up along the way. Always use that calculation and never had any problems with the Elecsa assesors either, so if must be right`ish`.

Cheers.....Howard

hey mate,

i find this a great way to calculate but i was just wondering you say to "apply diversity as required" but in your final answer it seems no diversity applied?? Just straight add and divide (which does seem loads easier )

cheers

I like easy, especially when it comes to doing sums.

 

[MarcT]

If you cannot bring your real-time demand down, then sometimes you can employ
a load-shedding device. Although mostly used on HVAC circuits, there could be
domestic applications (albeit limited) if there were no other alternative available.

 

[brucelee]

hi guys
i would just like to ask sirkit can you apply the calculation you described to all ie say total load before diversity is
2x 6A lights
2x 32A rings
1x32A cooker
1x40A shower
1x20A oven circuit
1x16A immersion
a total of 184A before diversity so 184x 0.4=73.6A after is this correct
what would be the max load before and after diversity you could safely apply to a 100A main fuse cheers

 

[sparks1234]

This is all very well but there is another side to this way of calculating it.
To keep the supposed maximum demand down you would need to keep the number of circuits down, by my way of thinking this may well then load up circuits and create its own problems.