Caravan hook-ups, RCD's not tripping @5XIn and earthing (PME)

[richy3333]

Hi all.

A local caravan site has asked me to test their RCD's. I popped in to speak to them about what they wanted and had a quick nosey around with a view to returning and undertaking the work.

The 32 electric hook-ups are fed via a 3 phase system which splits into 3 circuits. Each circuit is protected by a 100 mA RCCB, I think these are time delayed. Then at the hookup point each unit has 2 16A MCBs and they share a 30mA RCD unit as per Reg 415.1.1. (I note 708.553.1.12 and .13 says that each socket outlet shall have its own MCB and RCD etc).

The earthing system is definitely PME - I've spoken to the DNO engineer that installed it

When I did a quick test on a RCD at the hook-up it didn't trip out at 1/2 In but did at 1xIn and both parts of the waveform (o and 180 degrees). However when I tested at 5xIn my Megger kept reading back >50V. Does anyone have any idea why this might be? I tried switching over to the time delay setting but this had no effect, and as I say, they are standard 30mA RCD units. I tested several just to make sure it wasn't a dodgy one off.

I have a sneaky suspicion that there is no additional earth to the hook-up points and the manager thinks this might be the case too. Where the main incoming cable comes into the distribution box there is a separate 16 mm earth cable next to it running out into a soil pipe and into the ground. The DNO has a vague memory that originally an earth plate/rod was put in by a spark, but can't recall how long ago. The campsite manager is really helpful, but has only been there 3 years and there are no site records to show what has been done in the past. The owner has little interest and no clue either. (Incidentally the manager dug a test hole for me and we found the SWA cable serving the pitches barely at 30 cm with no additional physical protection/ warning tape or anything).

Sorry to sound ignorant but can I test this mysterious 16 mm cable by carrying out an earth fault loop impedance test as per GN3 page 17 to see if there is a means of TT earthing for these hook-ups? I have a Megger 1552 but no other specialist earth electrode test equipment?

Does anyone know how long earth rods/plates last for in the ground (sandy soil)? I'm just wondering if the site had a TT earth and it has corroded away and now not viable?

They also have 6 statics on site (3 belong to the caravan site and 3 are privately owned), that are fed from a different source (single phase) but also PME). The caravans are not far from the distribution board and on testing the RCD's either the Hook-up points or the main board RCCB's are tripping out at all ranges. However there is no time delay on these units and when testing it is somewhat a game of 'russian roulette' as to whether the hook-up RCD or the main board RCCB will trip out! Obviously this needs sorting out, but again the individual vans need their own TT earth? Is there any obligation upon me to notify the van owners that their vans are not correctly earthed and thus potentially dangerous under fault conditions? I have no way off obtaining the owners contact details unless the manager/owner wishes to advise me?

Any comments/observations would be gratefully received.

 

[malcolmsanford]

Think your first check must be the earth at each point. As you know from the the Regs and the ESQCR 2002 you can not feed caravan pitches with a PME, the static IMO should also not be PME as I would not class them as permanent buildings, but that is another argument. What you might find is that the SWA to the pitches is protected by the PME, but the pitches itself are TT. So the SWA would be connected to the earth at the origin and not connected at the pitches.

What you are going to have to do it check to see if you have an EFLI at your Pitches. This can be done either by doing a Zs or geting your R1+R2 at the pitch. I would first go down the R1 +R2 route as this is a dead test and you will be safer with this.

It seems a strange set up that each phase distribution circuit is protected by a 100mA RCCB only, what is providing the circuit with overload protection?

As you have quoted in your OP about the socket protection, was this install done under BS 7671-2008 or the 16th, I can't remember off hand the regs regarding this in the 16th.

So I would check from your SWA if it is Earthed back to the origin, and confirm that it is not connected to the pitches Then I would check at the pitch enclosure where the earths go to and trace back from there. You may find that all 32 pitches just have the one rod and this as you say maybe corroded or not even connected. It is really a case now of tracing things out.

 

[ukpablo]

this may be a long shot but i recently had the same problem but in a domestic dwelling. A 100ma RCCB time delayed main switch feeding a 63A RCCB(30ma) etc.....TT earth system 5 ccts on 30ma side.
Ze was good, bonding in place etc.

Customer said board kept tripping out randomly, however when i tested at the sockets with megger, it would not trip at all but would show >50v?????

So, i tested the RCD at board from the incoming side and it tripped ok??
this really bafflled me.........................after about two hours of changing the RCD, speaking to makers of DB eqpt i was still at a dead end.
i did the same RCD tests on other ccts fed from the same RCD with same result? (>50v)??
this is where it gets interesting, after doing IR tests on ccts there was a nicked neutral cable at one of the socket plates by the socket plate screw in the kitchen......................it was tiny. after re sleeving and connecting the RCD tested out fine??????????
So, how it affected the other ccts and did not trip the rcd regurlary is a mystery to me? (it was very random)
SO what im getting at is check the ccts for a possible fault as it may affect the RCD test.

Hope that helps and makes some sort of sense? took me half a day to sort it out?!!!!!!
Next time i will disconnect each cct at a time from CU to see if i can eliminate the problem cct earlier.

 

[nickblake]

If the pitches are rented then its up to the site owner to sort it out , i would carry out all of what malcome has said , i am taking it that the hook up points are the standard 16 amp sockets that you plug into , if this is the case make up a test lead with a 16 amp socket and 13 amp extension socket then its easy to test at this point and for stability reasons the readings should be <200 ohms TT at each point , one of the easiest ways to rectify this is to install an earth rod at each point and disconnect the PME earth to the point and connect the Earth rod to the protective conductotor at the hook up each hook up point should be RCD main switch ,MCB overload protective device with a maximum rating of 16 amps hope this helps

 

[SPARTYKUS]

Great post richy !

 

[Chr!s]

This will occur when the Ra is greater than 333 Ohms

5 X 30 = 150 Ma which equates to .150 x 333 = 50 volts

so anything above the meter wont test.

 

[Deleted member 9648]

Does the owner of the site have an EIC or previous PIR that you could refer to,this should give the info on the type of earthing etc.

 

[richy3333]

Great post richy !

Cheers dude. I didn't realise you were active over on this forum

55 days

 

[richy3333]

Thanks everyone for the quick and detailed responses. The work was definitely not done to 17th Ed and most probably 15th or 16th, but the manager cant say when it was installed.

I had forgotten that I had taken a couple of pics on my phone which might make things a little clearer.

The hook-ups are 16A and appear to be connected to the SWA and no other earth.


This is the cut out. Hopefully you can just see the 16 mm earth cable disappearing down the pipe (bottom left).


The other end connects into a Henley block arrangement and then feeds out to the 3 phases as per this photo.

 

[richy3333]

Does the owner of the site have an EIC or previous PIR that you could refer to,this should give the info on the type of earthing etc.

Afraid not wirepuller. There has never been any EIC's and certainly no PIR's supplied to the customer - This is the Highlands Last year the spark that checked the site just said it was 'OK'. Despite the site manager asking for the report, he never received it, and neither was an invoice forthcoming either. The customer would have been lucky if the spark was actually qualified and not just someone that owned a screwdriver

 

[nickblake]

Thanks everyone for the quick and detailed responses. The work was definitely not done to 17th Ed and most probably 15th or 16th, but the manager cant say when it was installed.

I had forgotten that I had taken a couple of pics on my phone which might make things a little clearer.

The hook-ups are 16A and appear to be connected to the SWA and no other earth.
View attachment 4784

This is the cut out. Hopefully you can just see the 16 mm earth cable disappearing down the pipe (bottom left).
View attachment 4786

The other end connects into a Henley block arrangement and then feeds out to the 3 phases as per this photo.
View attachment 4785

oh please tel me you dont have to take the cover off to get at the MCB's if that the case all the enclosure will have to be replaces so you can get at the MCB's as having to remove the cover to reset the RCD or MCB is totally wrong and exposes the user to live parts it should look some thing like this

 

[yellowvanman]

Don't like the use of an earth clamp on the SWA - although better than the site I have seen last week - none of the SWAs earthed at all - not a gland in sight!

 

[richy3333]

oh please tel me you dont have to take the cover off to get at the MCB's if that the case all the enclosure will have to be replaces so you can get at the MCB's as having to remove the cover to reset the RCD or MCB is totally wrong and exposes the user to live parts it should look some thing like this

It's OK Nick.
The MCB's and RCD can be reset by lifting the usual weatherproof cover. You do not need to remove the whole front cover to get at them

 

[nickblake]

It's OK Nick.
The MCB's and RCD can be reset by lifting the usual weatherproof cover. You do not need to remove the whole front cover to get at them

Phew im assuming its like the one in the pic i posted , i got worried for a minuit lol i have come accross the MCB's RCD in an enclosed box
well thats one good thing

 

[Graeme Harrold]

In the process of doing PIR's on a load of caravans on a big park. Half of the boxes do not have the flap to gain access to the RCD/MCB's and causes no end of teouble for the on-site spark.

WIth regards to the tripping on 5x, the earth will most likely be the problem. Is the site located close to the sea??? as salt in the atmosphere will speed up the corrosion of the metalwork. Pull back a couple of the SWA gland sleeves and check the SWA strands. COrrosion is apparant on the earth stud on the first picture posted. A simple Loop test will confirm the integrity and condition of the system, and yes the higher the reading, the less likely the RCD will trip at 5X....

 

[Engineer54]

Looking at that main DNO cut-out arrangement, are you sure the earthing system is PME?? I can see no N-E connection at the neutral cut-out position. I think this is a TT system, and a badly designed and installed one too!!

As Chris stated, many MFTs and RCD testers will not test when the 50 volt touch threshold has been exceeded, which means your TT system needs improving. At the very least each hook-up panel will need to be roded. And as this is, (as i suspect) a TT system, the SWA of the hook-up in-out supply cables can link those rods together...

I doubt very much if your existing Rods have corroded away, not if they were from a decent manufacturer, which should have a life of around 30 years, even in mildly corrosive soils should give at least 20 years service!! Now the cable connections to these rods is another matter, they can deteriorate especially if non-standard connection methods are used. Always best to exothermic or braise weld rod connections that are not accessable by means of earth rod inspection boxes....

 

[malcolmsanford]

The earthing system is definitely PME - I've spoken to the DNO engineer that installed it

Not having seen the pictures when I OP, but agree Engineer54 they does not look like a PME head, which leads onto the very worrying part of the Richy3333 post, as above, if the DNO don't know, on what looks like a newish installation, what they have supplied, it does not bode well.

Can understand in a way a 40-50 yr old installation but I thought the DNO by the ESQCR-2002 had to keep very accurate details now.

 

[richy3333]

Thanks Malcolm & Engineer54 for your comments. The DNO was adamant that it is a PME system, however I should be going past the site today so will pop back in as the pics I took do not cover the whole set up of the equipment. More pictures to follow

'Keeping very accurate details' around here just involves the DNO engineer confirming from memory. When I rang their engineering department, they had no idea they were supposed to be able to tell me the current earthing system and ringing the DNO helpline just left me banging my head against the wall - 'computa says nooo'

 

[SPARTYKUS]

Yeah....looking back at the piccy if it's PME then there's a green and yellow cable missing

 

[Engineer54]

The Supply may very well be from a DNO PME supply, but maybe the original installation electrician didn't want the available PME connection, just the neutral, probably because he knew that PME is not permissible for caravan supplies. So it is now, from that supply origin, a totally a TT based system...

A question, are those 100mA RCDs at the origin of each sub-main S-Type?? They don't look like it to me. In fact everyone of them is of a different manufacturer, which means at least 2 of these original RCDs have failed at sometime and have been replaced.

This whole installation really needs to be thoroughly checked over, and tested, before the holiday season begins....

 

[richy3333]

Thanks everyone for your help. What a great forum
As suggested it looks as though the DNO supplied a PME intake but the sparky installing the system chose to TT the whole lot. Having had a good look, the earth is definitely not connected to the neutral. There are no service pits to suggest a ground spike etc, so god only knows where the earth runs to. And, to make matters worse the likely area for it is close to the main incoming feed cable. The current warden seems to think the installation is quite old, he suggested 40 years, but I can't see that being the case. He is trying to contact previous wardens to find out some information as the current owner inherited the site and so doesn't know much about it. Great to have a helpful client

The main RCDs are left and middle, type B and the right hand one type C? so not time delayed as the warden suggested.

I have a meeting with them next week and have suggested a full PIR, which they want completed, subject to the owner agreeing to the cost. Regrettably they are not rushed about the importance of sorting things out and are opening this weekend. The 'dollar count' is as usual, more important than the campers safety

 

[nickblake]

you cant do any more than what you have suggested what i would do is to put it all in writing , because if some thing does happen and some one is injured or worse killed then you have covered your self

 

[richy3333]

Cheers Nike. Great minds think alike. I emailed a written doc to the warden this afternoon and he has acknowledged receipt. They understand the situation, but are driven by what the owner wants to do (make money). In fact the owner seems more interested in a planning application for park lighting than resolving and earth issue. That will all change when someone is injured and the HSE descend upon them!

 

[colinnot happy]

I believe we are the campsite richy3333 is referring to here and would like to address some of his comments:
“Great to have a helpful client” I, as the manager, am doing as much as is possible in the circumstances and the new owner is keen to get everything up to spec as soon as possible. richy3333 is in full facts of the tragic circumstances behind the very recent change of ownership and sarcastic remarks such as “Great to have a helpful client” do not reflect the desire of both the manager and the new owner have to bring this site up to and above standard. I came upon this forum while searching for the equipment richy3333 has advised we purchase.
“The 'dollar count' is as usual, more important than the campers safety” - I will wager any bet that no campsite in the local area, including those owned by large organisations, is putting so much effort into getting the required checks done to the correct standard (whatever that may be). As richy3333 mentions elsewhere most things in this part of the world are done on a wink and a nod - it is not and never has been good enough for me and I am offended by the remark!
“In fact the owner seems more interested in a planning application for park lighting than resolving and earth issue. That will all change when someone is injured and the HSE descend upon them!” There is, and never has been, any planning application for park lighting. This was something discussed by the previous owner and was dropped in favour of getting the correct checks done and any improvements made long before the start of the season. I have read the 9 page report provided by richy3333 and can find nowhere anything which he classes as dangerous and in need of urgent attention and we have acted upon any recommendations.
In summary: a “qualified electrician” installed all the systems on this site to the regulations current at the time of installation with the exception of covering one row of cables with protective concrete plinths - which I have discussed with richy3333 and the matter is in hand to be rectified as soon as is possible.
As manager I have in the past engaged what I have been led to believe were and are qualified electricians - they advertise as such in local papers and if they are not qualified I would have expected them to have been found out by now. If richyy3333 knows or suspects these people are not qualified I suggest he reports them to the HSE as it is they not we who are endangering the public! As manager I doubted their work and have now engaged richy3333 - if I have engaged another duff electrician would the good members of this forum please let me know and tell me where I can find one who knows the regulations backwards? I cannot see how I or the family who own this park could do more.
If I have learned anything in the last 4 years - and from reading this forum I am convinced of it - is that if I asked 6 electricians a question I would get six different answers! This is why I engaged yet another “qualified electrician” to take over the checking of the site.

 

[Farmelectrics]

sorry chaps brain freeze whats dno please explain

 

[Sintra]

Distribution network operator or in other words the electricity supplier.

 

[ukpablo]

distribution network operator ( supplier)

 

[tony mc]

Leccy Board

Distrobusion Network Operator