Caravan Park

Any thoughts on max fuse size to protect a 6mm ring?


On the basis you're happy putting a 20 A cable on a 32 A device, is there any problems with using the same "mark up" in your application?


Regards


BOD

There may be concerns already by the provision of 10 A devices for each of the 24 pitches. Was was the original device rating? A nail? 


Even if you were to use a 73 A device, you're looking at just 3 A per pitch..................


Regards


BOD

That was my original thinking in the first place BOD.

I thought I'd ask the question and defer to the, if not older, wiser heads on here.

You Sir being one of them.


George

Caught me out with your second post there.


The original device rating is the 100A mains fuse.


The first box is fed, via a 30mA RCD and 3core 25mm SWA to the first box on the ring, it then goes off in 6mm.


Bit of a lash up. 


There is a 100mA S type at the origin but the park owners decided to change the 100mA  S type in the feeder box to 30mA so their guests could reset the trip when and as necessary.


Feeder box with no lid, Incoming and outgoing single insulated SWA cores running up to and from the RCD, that kind of thing.


Not too worried that a 63A fuse in the feeder box would go as it's unlikely that all pitches will be in use at the same time (even during the height of summer).


George 

Table 4D4A RM D => 46 A for SP 6 mm² SWA. As BOD suggests, an ordinary domestic ring has a "mark up" of 1.6 x so if that is applied, we get to 73 A. So a 63 A OCPD is appropriate.


Diversity will sort out the rest. ?

Thank you Chris,


That was my original idea.

Sort out the feeder box with a 63A switch fuse and a 100mA S type RCD.


Give the local 30mA RCCB's in the pitch boxes a chance to work.


("They never go off that's why everyone knows to come up here and reset this one").

George

Or two 45 amp radials with two circuit protective devices and two RCDs, more capacity and only half the site goes off if there is a problem.


Andy Betteridge

Thanks Andy but I'll stick to my original plan.

A lot easier and you might be surprised to find how many vans fit on a 63A MCB.


I work on other sites that are much more heavily loaded, at least on paper.


Regards

George

Wait for the day people start arriving in electric cars with a tent in the boot .


Andy B.

well  given that up to 70 houses can share one 400A fuse on a substation,  perhaps the diversity 0f 60 or 80 A over 24 caravans  all with non-synchronised occupants is not as bad as it seems, and like the 100A company fuse per house, you could probably handle a 16A RCBO.

You just need to emulate the same slow blow characteristics as the substation fuse ! (60A C type or  a real fuse then.)

To apply the same scaling factor as the ring and its 13A sockets you really need to convince yourself that the any loading more than the single cable loading cannot be all within one quarter of one end, but is more or less uniform  around the ring.

Snapping the ring into 2 radial circuits of half the power has little advantage, other than looking more like a standard circuit, and maybe allowing a slightly higher total. This does allow  a ring round test to ensure that nothing has dropped off, and gives a better voltage drop for the folk at the far point.


On a related note I have always been amazed at how many caravans and tents can be hooked up to a supply and not give any problems in practice - one of my many hobby roles has been to be part of the team behind the wiring for the Essex Scout Jamboree (coming up again this summer so expect some tales of woe after the hols) and in the camping compound for those of us on the infrastructure side, it is a bit  more 'self service' compared to the side where the youngsters are, and there seems to be almost no limit to the no of 16A splitters that can be cascaded to  3 phase 63A supply. Well at least three or four of these sort of things   daisy chained up, plus a few Y leads..  The other side of the box  is full of  16A RCBOS, one for each of the 6 sockets that are on each phase.

Nothing short of a rewire will prepare this site, or indeed probably any housing estate in the UK either, for the wholesale roll out of electric cars. It works now because early adopters are few and far between. When that is required it is probably easier to have a dedicated car park/ charging bay beside the incomers with suitable billing as well.