OK Baldy, I've decided to play nice
Working on mobile units can be a bit of a minefield if you're not exactly sure what you're doing. I must say that I am no 'expert' but I have worked on them before. You sound like you are planning on finding hardwired supplies from wherever you take the trailer, if this is the case then there are a few things you need to take account of, the first one being.... The fixed supply
plug on your trailer needs to be
male, to be able to accept a
female socket on to it.
Secondly, you need to be able to make sure that the trailer is never used as part of a TN-C-S system unless directly under your supervision. This can realisticly be achieved in one of two ways; 1. relying on a rod and an RCD whenever you're plugged into a permanent supply (making your trailer a TT system), or 2. relying on electrical separation as your protective measure for if you're plugged into a generator. This method is by far the safest method of protection and I would choose this over ADS any day of the week!
The way to set this up is ultimately to wire as you normally would any installation with an RCD as your main switch, preferrably a 10mA, and making sure that all exposed conductive parts within the trailer are supplementary bonded to themselves and to the chassis (remember that this is
not an extraneous conductive part). The other thing worth noting is that you will not have an earthing conductor to your fixed supply plug as you will either be relying on an earth rod or on no earth reference at all. At no point will you want to be picking up an earth from the supply unless you can be absolutely sure that every single supply you tap into is TN-S.
If wiring into a permanent supply you'll obviously have to bang a rod in (wired from your main earthing terminal) every time you park up and do business. This will have to be tested on every occasion you do so and you will go through a few rods! lol. If plugging into a genny then you will be relying on electrical separation and therefore you want nothing earthed (
no rod!), only bonded to each other, which is effectively what your cpcs now become in each circuit. Bear in mind that your RCD is now useless when relying on a generator with no tapped earth. An ideal wiring system would be stranded cable to BS 7211 (I think) wired within plastic flexible conduit throughout the trailer. This is so you can get a 2.5mm cpc to every accessory to keep your ohmic readings between accessories negligable.
With regards to your supply, you really do want to be accurate about your demand. If you have a socket circuit which will only pull 2.5A then put it on a 3A MCB, if your lights will only pull 0.5A put them on a 1A MCB. The last thing you want is an installation on an unprotected 16A supply but with the potential to pull 38A (16A + 16A + 6A) if other stuff unrelated to you is plugged in.
I fear I am now rambling, my excuse is that I've had a few beers so feel free to shoot me down if I've left something out that I should have put in or put something in that I should have left out.
