Right or wrong?

[Rocboni]

Recently our family friends had a supply installed in there winter yard (travellers/showmen), being a trainee and having just covered special locations section 708 at college,I was interested to see how it Was done.

Supply is as follows.

3 phase TNS supply
25mm tails to 63A 4 pole switch fuse
20M run externally 16mm 4 core supplying TPN 4way board located in the centre of the yard (swa as earth)
Located in TPN board
6x 32A RCBO each supplying a 32A outlets via a meter for individual caravans
2x 32A mcb feeding a 40M 4 core 10mm to a second box with 2x16a 2x32A sockets
Arrangement of second box
1x32A and 16A one each phase with its own neutral through a 32A kWh meter 32A skt protected by 20a RCBO 16A skt protected by 16A RCBO. This box is TT with the armour of the 10mm earthed via the TPN board but isolated from this box. 3 earth rods linked via 16mm each anout 2M apart.

My understanding is that all supplies For caravans should be TT so my question is should the first TPN board be TT? however it would be difficult to locate rods as where box is located is concrete but caravans stand on gravel so this is possibly why they did not TT the supply?
Second question is it ok to run two single phase circuits in one cable protected by two separate MCB no shared Neutral as the 4core is L1 L2 N N
Some of these caravans are the size of acrid trailers but I guess it would still come under this section of the regs?

 

[westward10]

Not sure it applies as Section 708 is for leisure vehicles.

 

[Richard Burns]

A TNS earthing system is permitted for caravans as it a TT system; it is only TNCS (PME) that is not permitted.
Two circuits can be run in the same mulitcore cable; circuits are not allowed to be split across SWA cables where the line(s) and neutral run in separate cables.
Generally it seems OK, possibly a bit of short cutting on the installation but not dangerously or not in compliance.
The use of 20A RCBOs for the 32A sockets means the 32A breaker is redundant as the 20A breaker limits the current.
If the sockets are fully laoded then you are probably over the limit on volt drop on the 40m run of cable but a basic loading shoudl be OK.

 

[Rocboni]

So could the TT have been ditched and the armour used as the earth on the 40meter run, as there is no upfront 100mA rcd or double pole isolation with the RCBO being single pole devices only?

 

[Rocboni]

There is a 16Askt (16A RCBO) and a 32A skt (20A RCBO) tapped off the one phase so there is a possibility of drawing 36A max per phase, but both skts are protected by the 32A MCB so 32A is limiting current, not redundant?

Sorry just trying to fully understand this for future reference.

 

[westward10]

I think you have some spelling mistakes.

 

[Richard Burns]

If there is no double pole isolation on the TT parts then this a not so good, normally Caravan RCBOs are double pole.
Possibly the 4pole isolator may be considered the isolation?
As you have full 30mA protection there is no need for an upfront 100mA type S.
TNS could have been used throughout.
I think I mixed up the 32A sockets vs 32A MCBs
you have an arrangement for the remote sockets something like this?

If so then volt drop is OK.

 

[Rocboni]

Yes that is correct.