Max demand and diversity

[Dm7192]

Looking for some assistance here, been asked to calculate the max demand and diversity for the supply authority who are installing new main armour to a domestic building which I am rewiring.
When calculating the max demand do I use current rating of the circuit breakers for the individual circuits or do I anticipate each circuit load? Some circuits are easier than other for eg. The shower rating is a plain and simple 10kw however when trying to anticipate the load demand of a ring circuit at a given time this is complex as it will always fluctuate therefore do I use the 32A mcb rating as reference. When I do it using a projected demand my load is Roughly 150A/34.88Kw after diversity surely this is inadequate for a 100A main switch in a domestic Board yet if that's what it works out then what else can I do?

any assistance would be greatly appreciated here thanks

 

[telectrix]

add up the MCBs and then x 0.4. what's the rating of the supply fuse?

 

[Octopus]

Lately I've been using 0.3!

 

[Guest55]

lets just say in this house there are 7 circuits...
6a up lights
6a down lights
32a up sockets
32a down sockets
16a garage
40a shower
32a cooker

in total thats 164a

times this by 0.4 ( the recommended domestic diversity figure ) = 64.6A
that is your max demand for the property.

 

[Dm7192]

Is that the recognised method or a rule of thumb method for sparks?

 

[KAS1]

That works spot on for my property and I have a 3phase 60amp supply

 

[Guest55]

Is that the recognised method or a rule of thumb method for sparks?

its rule of thumb just for domestics.
if you break it down for each circuit sperately you can get the final figure down even lower.
but commercial / industrial diversity is a whole different ball game lol

 

[Dm7192]

Ok I'll give it that a bash
thanks a lot appreciated

 

[Octopus]

You have to remember the current rules for diversity were agreed when houses had 4 or 6 fuses. Most houses how have 10+ way boards and have eco devices!

 

[Engineer54]

You have to remember the current rules for diversity were agreed when houses had 4 or 6 fuses. Most houses how have 10+ way boards and have eco devices!

Maybe, but nothings really changed that much, just that loads have been shared over more MCB's etc. The only real change from yesteryears in domestic installations, is the use of electric showers with idiotic KW ratings and bigger cooker appliances. Even with all the modern appliances it's still doubtful you'll see more than 50+Amps or so being drawn, and not for very long either!! lol!!

 

[ackbarthestar]

The only way you will know for certain what the Max. demand for a specific property is likely to be is to Clamp a similar property with similar loadings and turn all their appliances on. (let them know before hand, of course )

You'll soon see that the real buggers will be the 3 instantaneous water heaters installed in the on-suites.

But as you will see the application of diversity to the max. demand is usage over time.

The regs allow for overloads for short periods. That's not to say that 3 * 10.8kW electric showers left on for a couple of hours won't have a deteriorating effect on the service fuse, or the tails

The common ROT, as others have stated, is 0.4 to the max. demand.

 

[kingeri]

Shame we can't just put the rating of the main service fuse as the max demand on domestic jobs, cos that's what it is really, if you see what I mean!

 

[telectrix]

Shame we can't just put the rating of the main service fuse as the max demand on domestic jobs, cos that's what it is really, if you see what I mean!

that's another acceptable way. you could argue that the max. demand is limited by the rating of the supply fuse.

 

[kingeri]

that's another acceptable way. you could argue that the max. demand is limited by the rating of the supply fuse.

And it's the quickest way!

 

[ackbarthestar]

I agree, there's nothing stopping you from putting 23, 18.4 or 13.8kVA for residential properties

 

[telectrix]

provided that you can access the fuse to see the rating. otherwise, base it on the size of the tails.

 

[ackbarthestar]

Not sure i would agree with sizing the Max. Demand on the size of tails. Its not uncommon to see 100A Service fuses (well that's what it says on the packet) and 16mm2 tails.

 

[telectrix]

Not sure i would agree with sizing the Max. Demand on the size of tails. Its not uncommon to see 100A Service fuses (well that's what it says on the packet) and 16mm2 tails.

my thinking there is that the max. CCC of the tails would limit the demand. e.g. if 16mm tails, max. demand 80A, irrespective of the fuse rating. just throwing the idea out.

 

[Brightspark2]

its rule of thumb just for domestics.
if you break it down for each circuit sperately you can get the final figure down even lower.
but commercial / industrial diversity is a whole different ball game lol

Domestic x 0.4
Commercial x 0.6
Industrial x 0.8

Seen that recommended somewhere, wiring matters maybe...

 

[ackbarthestar]

my thinking there is that the max. CCC of the tails would limit the demand. e.g. if 16mm tails, max. demand 80A, irrespective of the fuse rating. just throwing the idea out.

I suppose its a possibility, Anyway, domestically speaking, Its quite difficult, and expensive, to consume 80A on a continuous basis unless you have tropical plants in the loft :39:imp2:

 

[telectrix]

mmm... pass the dutchie.

 

[Knobhead]

You cooking Tel?

 

[Engineer54]

Domestic x 0.4
Commercial x 0.6
Industrial x 0.8

Seen that recommended somewhere, wiring matters maybe...

I wouldn't just go applying those factors to commercial and industrial installations. Now your in the realms of real electrical installations and as such, need to be assessed far more stringently than a typical domestic installation....

 

[Knobhead]

Where did 0.8 for industrial come from? That’s got me curious.

 

[johnboy6083]

There Are diversity figures suggested in the Electicians design guide by the IET. It has paper mills, rolling mills ect. I'm not sure i would 100% go with it though!

 

[ackbarthestar]

Where did 0.8 for industrial come from? That’s got me curious.

Me too....

There's all sorts of things to take into consideration which are often specific to the installation

 

[Guest55]

anything bigger than domestic and i apply diversity on a circuit by circuit basis , trying to use a single generalised figure on a large commercial install will end in tears and lighting wired in 25mm lol.

 

[Engineer54]

There Are diversity figures suggested in the Electicians design guide by the IET. It has paper mills, rolling mills ect. I'm not sure i would 100% go with it though!

It's a good job then, that the larger commercial and industrial installations aren't designed by electricians then!! lol!!

 

[Guest55]

It's a good job then, that the larger commercial and industrial installations aren't designed by electricians then!! lol!!

why are you saying we're not capable ?
i've just recieved the elec drawings for the next stage of the project im working on now , designed by some big shot consultancy - they're a load of pants , completely ignoring the concept of positioning db's at the geographical load centre to reduce final circuit lengths.
;-)

 

[Engineer54]

I'm not getting into an argument on this issue, because their is good and bad in most areas on the design side of things.. But generally speaking an electrician would not be capable on designing the complete electrical installations for a large commercial or industrial project, and would never be asked too either.

Having been in and experience of working in a design office, i can't tell you how often it is, that the Engineers are working initially without the full details, so will generally often submit a concept drawing as a 1st issue. The Resident Electrical Engineer, or manager will then conduct a design review, marking/clouding the drawings up, complete with comments and return to the designer. REV 1 will then become the first ''working/installation'' drawing... But due to continuous changes, the final ''As Builts'' could be up to REV 6, 7, 8!! i've known one drawing to have 19 revisions!! ...lol!!!

Design review is initially my biggest element of work on all my projects, and were talking about literary 100's if not thousands of drawings covering everything from basic final circuit layouts, ELV systems, mechanical plant and controls, to external/internal MV and LV main distribution...

 

[Guest55]

i'm only pulling your leg E54.
;-)

 

[Engineer54]

i'm only pulling your leg E54.
;-)

Thank god for that !!! ...lol!! :smilielol5: