Touring caravan supplies

[brianmoooore]

Anyone on here with knowledge or experience of wiring for a touring caravan/camping site, whose brains I can pick, please?
I may have to design and install supplies to a C and C club certified site. That's a maximum of 5 touring caravans or motorhomes, plus 10 tents.
There will be a sub main from the supply source to a small facilities block, and from there two strings of 7 x 16A sockets, arranged in pairs, each socket individually supplied from a RCBO.
Distance between pairs of sockets will be around 25m, so the furthest sockets will be around 180m from the facilities block.
What sort of current should I allow for each socket, and what loading should I assume when doing voltage drop calculations for the furthest sockets?
The ends of the two strings will only about 25m apart, so would it be better to install as a single ring?

 

[littlespark]

When my father in law had a site, we dealt direct with Rolec for hook ups… but I believe there are other suppliers.

The site was wired before I got there, so how “right” it is, I’m not sure.

We had 4-6 touring sites on each ring, 40A in 4mm, and a couple of radials on after a jcb accident.

 

[pc1966]

If they are all RCBO then a ring makes sense as you have lower voltage drop for a given cable expense.

However I have no idea what diversity factor you should apply to the overall supply OCPD relating to that! I would be tempted to assume something like 10A per caravan (typical full-fat kettle) so around 63%, which would make it around a 70A supply (if single phase), or maybe go a little lower to a 63A MCB.

That is about double the 'standard' RFC and in 4mm its VD limit is 171m so I would expect a 10mm ring from 63A to be broadly the same and OK for your 180m ring length (if I understood it right?).

As all caravans will be TT you won't need CPCs as such to each point, but almost certainly the supply in SWA you might struggle with OCPD disconnection if using 2-core SWA. However putting a 100mA (or 300mA if worst-case of 7 * 10mA accumulated leakage worries you) delay RCD for the supply would allow for that and selectivity with the RCBOs.

 

[brianmoooore]

It's the diversity to apply that I'm unsure about. I have a touring 'van myself, and know from experience that high current draws tend to be short and sharp. Typically, an electric kettle and microwave oven running at the same time, and the chances of all the 'vans doing this at the same time are slim.
Possibly the highest long term current draw would be air con running at the same time, in several 'vans.
The sockets for the tents would typically have a much lighter maximum demand. There might be the odd kettle or microwave used occasionally, but typically the load would be a couple of LED strings and a 'phone charger.
If I can get info. on the diversity to apply, I've no problem doing the actual calculations.
The available supply is two phase (230-0-230) so that should help with cable sizes.

 

[pc1966]

It's the diversity to apply that I'm unsure about. I have a touring 'van myself, and know from experience that high current draws tend to be short and sharp. Typically, an electric kettle and microwave oven running at the same time, and the chances of all the 'vans doing this at the same time are slim.
Possibly the highest long term current draw would be air con running at the same time, in several 'vans.

I'm surprised there is not an industry figure for this. Any idea of the A/C demand? Assuming only that per caravan would probably be a safe bet to get the total for the supply.

The sockets for the tents would typically have a much lighter maximum demand. There might be the odd kettle or microwave used occasionally, but typically the load would be a couple of LED strings and a 'phone charger.
If I can get info. on the diversity to apply, I've no problem doing the actual calculations.

OK

The available supply is two phase (230-0-230) so that should help with cable sizes.

Yes, as high-ish demand would be fairly balanced so you could assume negligible neutral drop.

 

[littlespark]

I believe the AC along with the lights will be on 12v.
Most tourers come with a suitable sized microwave, and there are small size kettles.

All heating and cooking is gas (although in mine, there is one electric ring and 3 gas)

It doesn’t stop people bringing other plug in equipment, such has heaters, but by design, there shouldn’t be anything near 16A per pitch.

We found the static owners were more likely to have quick boil kettles, a washing machine in the unit, George Forman grill and any number of pkug in heaters, even though their vans were centrally heated.
One woman had a 9kW shower fitted by her son, which of course just tripped the 16A

 

[pc1966]

I believe the AC along with the lights will be on 12v.

So engine-driven?

Otherwise I would be surprised as a 12V motor is unlikely to be used at 20+A so 240W and that is small in terms of heating/cooling for even a small room.

One woman had a 9kW shower fitted by her son, which of course just tripped the 16A

Oh dear...

 

[littlespark]

Touring caravans have a 12v leisure battery, which is charged either by 230v mains, through the vehicle when towing or solar pv on roof.
The lighting, 12v aux sockets, heating controls and water pump come off this.

There is only a handful of 13A sockets, which of course only work when the van is plugged in.

TV, aerial amp, microwave and kettle are on mains. As is battery charger, and the fridge can run on 230v AC, 12v DC or LPG.

We’ve got an external 13A socket on the side which supplies anything in the awning…. For us, just some fairy lights.

 

[R-fur]

I did some work for a large caravan site a few years ago and had some discussions with the site owner about consumption. A lot comes down to whether its a metered supply or not. If its metered the punters will tend to be more careful about how much they use, if its un-metered then they may just stick on the fan heater.
Metered supplies are a pain though as you need to supply meters, do the readings and bill out. Un-metered then a 10A MCB will limit the usage, especially if they are in a locked compartment.
For diversity I would have a chat with the site manager about the anticipated usage and try and come up with an after diversity demand for each socket. Say 5A per socket for a van pitch and 2A per socket for a tent pitch. Multiply it out and there is your max demand. It is important to get the client on board at this point and make sure he understands the balance.
Higher max demand = cost, lower cost = nuisance trips.
Volt drop, again discuss the design criteria with the owner and let him make the balance calls, ie cost against flickering lights. Agree a likely worst case, say 20A draw at the final pair of sockets and do your volt drop based on that.
Allow for several earth rods down your route.
Note down your calculations and values agreed with the site manager so that you can refer to them in any future discussions.

 

[brianmoooore]

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

 

[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.