Testing static caravans at a trailer park, all have there own rcd unit and are connected to a supply unit with meter which is also the protected. Issue I have is I'm unable to locate the origin of supply, done all dead test and it's tested out fine, done a as reading and got a big impedance value of 380, i assune its a tt system but until i find the origin I can't tell. Even for a tt this is to high with I will note on a separate test sheet for the supply feeds. Issue is that if i test for as if course the readings will be to high. Ino that you can ober come this with using an rcd, but does the trailer pass or fail, if connected to a supply that has good impedance values then it would pass but connected to sky high reading then it won't. Or as it's protected with an rcd, is it okay and down to the park to then address the high impedance values? Sorry it's long winded I hope you understand and any advise would be great thanks.
It sounds as if you are there to test the caravan and not the site. As such you would treat the caravan connection point as the origin of the installation and the site wiring as a private distribution network. Assuming that the pitch is protected by a 30mA RCD, 380 ohms whilst high, is well within the maximum of 1667 ohms allowed. I would highlight your concerns regarding the high impedance, but give a satisfactory.
The site is dur to be tested this summer. Excuse my misunderstanding but I thought the maximum allowed was 200And the higher value only allowed at the distributors spike?
No, BS7671 warns (table 41.5) that an earth electrode resistance greater than 200 ohms may be unstable.
Oh yes, but that would be something for your client and the site administrators to discuss. You may get asked to install another rod at the hook up point?
Surely you can quickly check the origin to see what the earthing is? Could be a TN with two core armoured, the armours rotting away.
The caravan should have its own consumer unit. This should be connected via flex, usually blue arctic flex to a bs4343 round blue 16amp plug Into a socket. This socket should be in an IP rated meter box with an RCD and trip switch. This is fed of a three phase cabinet containing a trip or trips for each phase, which are usually arranged according to the rows of caravans. It will be there amongst the caravans unless its a small site and housed in a building. That will go to a main panel and to the mains . its a lot of connections.
Yeah they are done like that but there new to the site and haven't a clue where the mdp is. I've found one do far but the supply isnt from there. There two core with earth via the sheath and as you say alot are rusted as the glands sent ip rated. I was thinking when the time comes to TT each power point. The one panel looks like a tncs but other parts of the site are TT. Could be due to cable run tho and they haven't exported the earth.
I borrowed a small generator when I tested caravans as other wise could not test caravan RCD site RCD would often trip first, so actually tested on a TN-S supply. Lead was also tested with PAT tester and I had a converter to run PAT tester from 16A outlet. The PAT tester I used tested the supply first. I am sure with that high of an earth loop impedance the PAT tester would have locked out. Where the caravan passes and the supply does not with touring caravans then OK to pass caravan, but in your case if it was me I would simply report in writing that there was a supply problem and return latter but with static caravans they are not actually classed as caravans but mobile homes and you can have a TN-C-S supply hard wired in. Often there is no lead set and no way to test other than with the normal supply. So job one is decide if really a caravan or if really a mobile home?
I suppose there really a mobile home then as you cannot move them unless towed. Some are wheeled otheres are not. But It's set up as if people as t to move plot or site they can. So a hard wires tn system wouldn't be ideal. There are others that are built on site with a hired wired supply. Trouble is even if the supply atm is a tn supply it foesnf not resolve the issue of high impedance. I could replace cables and glands as they look in a tough state but the simpler option would be to tt each point. I have found one panel but it doesnt feed that site of the site. I have found a small 3 phase board whjch is a tt system and supply about 5 local points. These have a low impedance value tho so no real issues there.
If it was a TN, you should be sorting the high impedance issue, as there would effectively be no protection on the distribution.
I first need to find the source of supply but as no one knows where it is then that's a struggle. I'll note in the test cert that it' needs urgent attention.
The only panel I've found does appear to have mccbs with add on earth leakage protection. That panel is a tncs farthing system. Just don't think it's feeding that part of the site.
I think it is vital to know what the earthing arrangement is here. You should not mark it as 'satisfactory' without knowing what the earthing arrangement is.
Been back to the site today and found several boxes with fuse carriers in. The 16A units are then feed from here. It's a tncs system with the metal sheathkng being used as a farthing conductor. Apparently they have had someone go around and install earth stakes. Would seem an easier option from liking at it to run a single earthing condctor to the fuse carrier box then from there to each point. But It's up to who's doing it I guess.
Earth rods wont help the fact the cables got no protection if it has that sort of earth loop and no RCD.
Apparently it's not my issue. I spent an hour get very frustrated with the people in the office trying to express it's dangerous and need to be sorted. They didn't seem at all bothered. More worried about getting there money. Only other way would be to change the mccb for one with and rcd attatment. I've given up trying to explain to them tho. Just worried me that when testing the Dr ov the caravans it's connected to there silly and that's what I have to record. But customers always right
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