Touring caravan supplies

[pc1966]

Did a little online research into caravan aircon units, and it turns out they draw less than I expected. A popular Truma model only draws 4.2A (albeit with a hefty 28A start up surge for 150mS).

Is that at 230V?

Supplies definitely won't be metered, if you want customers to return.

From the above, it might make sense to look at 10A C-curve RCBOs so they won't trip on the start-up of the A/C but the folks know they can't push too far.

In the apparent absence of any national standard for diversity, I was thinking along similar lines to R-fur above.
6A per caravan/motorhome outlet and 2A per tent outlet, gives a total design load of 50A, spread over the two available phases, so 25A each.
Cables sized to give 5% drop at the furthest socket, assuming the full 16A drawn from that socket, and 6A - 2A being drawn from the other points along the route.
Sound about right?

That seems quite reasonable. I would be inclined to still use a delay-RCD for fault to earth protection and then look at pushing the OCPD up as far as sane to get better selectivity with the RCBOs and so a short-term overload causes a brown-out instead of a total cut off.

For example, if you are looking at 6mm you could even look at a 40A D-curve MCB (Hager selective to about 0.5kA with thier 10A C-curve RCBOs), as a 300mA delay RCD would meet your disconnection time on cable faults, while being selective to a 100A supply fuse to 4.2kA

If the supply fuse is smaller, say 60A, then you would be limited to something like a 32A D-curve or 40A C-curve to have any supply-side selectivity, and then load-side selectivity is down in the 0.35kA region.

Or use a 40A switched-fuse which would be better for selectivity both ways, but I doubt that is so good here due to the hassle of the owner having to replace a fuse if a fault to really bad diversity situation occurred.

 

[brianmoooore]

Thanks to all that have replied. Gives me something to start working with. 300mA delayed RCD seems a good idea to incorporate as well.
I know from experience of the sites I've stayed on with my own 'van, that 10A C curve seems to be the 'standard' MCB for a 16A socket. I find from helping out those that have lost their supply (no such thing as a total holiday - always on call), that caravanners usually have a fairly good knowledge of what loads they can switch on without risking losing power.

 

[pc1966]

Are you thinking of taking the 230-0-230V round in a ring, rather like 3-phase, with alternated outlets on each phase?

Or just using it as two physically separate single phase circuits?

I expect a 3-phase RCD would work with just N,L1,L2 used here, but it might be worth asking the manufacturer. DP MCBs are easy enough.

Having two separate single-phase rings is easier for anyone else to fault-find, so there is some advantage there, but it potentially costs more in cable (due to N drop, doubling up lengths, etc) and if properly documented and copies left in the DB should not be a problem.

 

[brianmoooore]

230-0-230 around in a ring, with each pair of outlets on alternate phase.
3 phase, four pole RCDs work fine on two phase, as long as you ensure you use the poles that have the test button connected to it. Loads of two phase around my neck of the woods, and I've been using 4 pole RCDs with one pole unused for decades.
The common neutral would help with voltage drop, but for design purposes I need to assume that one circuit has the full (diversified) load, and the other is unused.
Done a few rough calculations, and it looks like it's either going to be 6mm2 or 10mm2, depending on the exact layout of the site.