diversity

[metro155]

hello, 

I have been asked to look at at job in caravan park to provide a supply to 12 new 16amp bases. 

The question was what type of diversity would one apply to the cable calc?

I was planning on installing a buried multicore cable to a splitter box close to the 12 bases.

installation is

1) tt (will be installing correct rcd protection)

2) 221meters from dno to splitter box location

3) cable buried by itself 

thanks

 

[Sharpend]

Ok so what calls have you applied yourself? 

 

[metro155]

Thanks for your reply.

To complete my clacs I need to determine the load so

12 x 16amp is 192 amps.

It wouldn't be practical to do my calculations of this figure as the cable would be overkill. 

This brings me to my initial question. Would it be practical to think that on any one occasion only half the twelve caravans would be pulling full load so a diversity of .5 would be applied. 

On a side note these caravans my not have gas central heating and on a cold easters night the good old 2kw convector heaters will appear.

I appreciate your input thanks.

.

 

[Lurch]

You don't need to do 12 x 16A. A lot of these hookups are protected by 6A MCB's (IME). I would clarify whether you actually need to supply the full 16A to all outlets, or maybe to mitigate the risk of all of them pulling the full 16A on all or too many then do it the other way, just supply it on a 60A and base your calcs on the CPD rating, not the load.

 

[Adrian]

3 phase it 

 

[metro155]

Thanks for your reply. 

The sites policy states that caravans have a 16amp supply to each pitch. These caravans are of the static type not tourers. 

Sorry should have mentioned that.

 

[Adrian]

Section 708 of bs 7671

 

[metro155]

Section 708 does not include any information regarding diversity applied to static caravan supplies.

I was asking if anyone could give me some practical advice on the diversity to be applied to the 12 new bases not how to install them

 

[Adrian]

You answered your own question the site owners require a 16amp supply to each van 

 

[metro155]

Diversity is the question I'm asking. What diversity would one apply to the cable calculation if I was to supply 12 caravans rated at 16 amps each. It wouldn't be practical to do this at full load which would be 192 amps?

 

[Andy™]

well if they can be expected to pull 16a each (you did say heaters would be used_ then you cant really apply much diversity. unless you want the OCPD to keep tripping when its cold and everyone is next to the now cold heater whilst someone has to go turn it back on...

 

[Sidewinder]

If the specification says 16A per caravan for every caravan, then you can't apply diversity, what does the spec actually say?

What is the incoming supply?

If the incomer is only 60A/ph, then no point in putting a cable in bigger than 60A, unless the customer advises you that they are going to get a supply upgrade.

 

[metro155]

It doesn't seem practical to assume all caravans will be pulling 16amps exactly the same time.

 

[Sidewinder]

I didn't say it was, but, if, the specification calls for it then that is what is needed.

What does the designer require?

 

[apprentice87]

It doesn't seem practical to assume all caravans will be pulling 16amps exactly the same time.

They will mot be far from it when everyone gets up at around the same time in the morning and turns their 2 or 3 kW heaters on..

I would have a three phase supply, work out cheaper anyway..

What supply you got now?? That is one LONG cable...

john..

 

[ProDave]

You can't design this if you don't even know what supply you have?

At that length of run it's going to be a big cable, just to get voltage drop to an acceptable level, the cable will probably be a lot larger than just necessary for the current carrying capacity.

If it needs a new supply, then get the DNO to quote for a new supply head a LOT closer to the 'vans.

I have seen a lot of really poor caravan site installs, so probably what will happen is you will design it properly with some big cables, and someone will quote cheaper with an under rated job, and that is what they will choose. Make it clear in your quote why you have specified big cables etc.

 

 

[metro155]

this is an existing supply of 100amps three phase. Customer assures me that an application for supply upgrade has been filed. He wants to start the wiring for the new bases so that they will be done when New supply is connected. 

A new switch room is being built beside existing supply. A new ground mounted transformer 400kva is being installed. And obviously New switchboard etc

 

[SPECIAL LOCATION]

Thanks for your reply. 

The sites policy states that caravans have a 16amp supply to each pitch. These caravans are of the static type not tourers. 

Sorry should have mentioned that.

It doesn't seem practical to assume all caravans will be pulling 16amps exactly the same time.

Diversity is the question I'm asking. What diversity would one apply to the cable calculation if I was to supply 12 caravans rated at 16 amps each. It wouldn't be practical to do this at full load which would be 192 amps?

If you are hoping for someone to say oh the diversity calculation for static caravans is 75% of the first four vans and 45% of the next eight vans. then you will be disappointed....

You are the one who needs to establish with the customer exactly what they want... 

and the types of realistic load expected.

e.g. are the vans only used during holiday periods or are they some of these semi permanent lived in statics?  How often is the site full? How many final circuits and what rating are in each van ? etc. etc.. 

If you go back and re-read about diversity, excluding the few minor common domestic circuits given as illustrations of how diversity can be applied,

it is primarily up to the designer to establish with the client the types of loads and thus supplies needed. 

The paragraph in Guidance note 1 Appendix H.. (or appendix A in On-Site-Guide),  states that it is impossible to provide standard set of calculations for every installation..

It is your specialist knowledge of the customer and type of installation that they want, that governs what diversity you will consider appropriate or not to apply.

If the site policy states that every user has access to a 16amp supply then maybe you need big cables.

Unless they have a sub-clause saying during busy periods supply may be limited.

I would guess in the real world not many would be pulling more than 10Amps for any significant duration..

How well are they insulated, do they have electric ovens?

A 750watt convector heater can heat up a small area quite comfortably.

What other cooking appliances are included...

Caravan kettles ovens and microwaves can often be lower power item...

But in statics they may be full blown household appliances...

What about vacuum cleaners..? 

Are there other existing vans on the site ? 

if Yes...  what power do they draw? 

Guinness  

 

[Andy™]

100a TP is adequate for running 12 caravans at 16a. on the plus side, total would be 64a per phase. but you would most likely need a bit more for communal lighting etc. depends what else is already being supplied by the 100a suppl though

 

[ProDave]

Most static vans use gas (lpg in bottles) for cooking, and often for a gas fire in the living room to keep electricity demand down, but then usually use small panel heaters in the other rooms.

Insulation is about  1" of polystyrene if you are lucky, i.e in practical terms, none.