4 consumer units in one house Help

[James Warren]

I have just installed 4 new split consumer units in an old edwarian house. The boards are not in the same place and are being fed by the meter in a barn about 60 meters away. Very unconventional setup. The tails (25mm) come into the kitchen and I have put the feeds for 3 of the boards through a 300ma rcd to protect the cable but this is making it impossible to test with my KT65 as it sometimes trips the 30ma rcd on the CU and sometimes the 300ma on the incomming board. Would I be better ommiting the 300ma rcd and just putting 100A incommers on ? The wiring is a mixture of 16 mm twin with a seperate earth (that seems ok) And the feed for the upstairs consumer unit is 16mm twin and earth (but has very little load. ) Hence the reason for the 300ma rcd in the main board. Obviously if that trips most of the house is in darkness so not good. I have told them that in my opinion it's much safer than the old fuses it had but obviously falls short of modern 17th regs. The small earth is an issue going to the upstairs. When I try a loop test with both rcds inline it just says no. (But I know it's intact) Other times it just trips the 300ma rcd (which I'm beginning to suspect is faulty). If I do the same test on a downstairs circuit it just gives me a correct reading (0.60 ohms which is ok considering the distances And 0.86 at the furthest socket) Replacing the cables is out of the question at the moment and I'm just trying to make it safe.
Anybody got a better sugestion ? I'm veering toward taking out the 300ma rcd ?
My first post so be gentle.

 

[Octopus]

What tests did you undertake on the house prior to installing the new CU's

What tests did you undertake while doing your CU changes?

What have your scheme technical support suggested?

 

[Des 56]

I dont want to get embroiled in questions about the install,no time sadly,but just one question
Is the 300m/amp an S type

 

[James Warren]

Ok I did a earth loop before I started on a few ciruits which gave results I would be expecting for cable run etc. The insulation test were high on 2 circuits (one was a bell and the other has been disconnected) All rings are intact with readings between 0.2-0.6 live to live earths are consistent with those readings. (depending on length). I am not part of a scheme (we have no part P here in Scotland). I did the same tests afterwards but am having problems getting a reading for loop. The machine either trips the 300ma rcd or comes up with "NO". I think I may have to take the 300ma out or do you think I'm suspecting the wrong thing ?

 

[James Warren]

It is an S type
Is that the problem ?

 

[mogga]

s type could be causing the problem

 

[telectrix]

or link out the 300mA RCD to do tests. don't forget to remove links after.

 

[James Warren]

So you would leave the 300 ma one there ? I'm thinking along those lines but whatever I can't have this thing nusence tripping as it is the feed for 3 of the consumer units and all the lights (that would be ok if the cable was drilled through but otherwise the 30ma rcd's in the C/U's must trip without this one tripping. I'm going to bridge it out later and see if I get results on a loop.
Thaks for the advice guys.

 

[telectrix]

if the tails to the CUs need RCD protection because they are buried <50mm in walls, to comply with BS7671, they require 30mA RCD. therefore your 300mA RCD is not compliant so you may as well remove it and note it as a departure.

 

[SPARTYKUS]

Hi James Warren

lucky you no Part P !

I'd be inclined to run new sub mains in armoured. Then forget any up front RCD protection. Assuming you have a TN earthing system ..... ?

 

[Guitarist]

Apologies if I have read this incorrectly, but did you say that the 25mm tails are 60m long, running from the meter in a barn?

 

[James Warren]

I'm beginning to think putting in the 300ma rcd was a mistake. As you say it must be a 30ma for the regs. So I'm going to remove it and just have 2 100 A switches. The origin in the barn is A TN 100A incommer and old swichbox with an 80A cartidge fuse in it. The meter is also there as is the radio meter for the heating. It is then put through a 3 phase cable 3 live one neutral (I still have to connect the heating and mark the wiring) Obviously it would help if it was on when I'm there as it's been dead at the times I were there. I actually thought it was an old unused cicuit (easily done when there are no meters and both tails appear to be line conductors lol) I personaly would be happier if the wiring from the first consumer unit to the other 3 was renewed and I will state that in my report.
Cheers for the input guys.
It's a unique installation and I think it's a case of making it safe without ripping the house apart.

 

[Jimmyb]

two words 'good luck'

 

[malcolmsanford]

I 'm still trying to get my head around the 300mA RCD and why to be honest here?

 

[James Warren]

Ok the reason for the 300ma rcd is the wiring is old and surely better to have some fault protection than just a fuse Plus because I have three runs of the stuff inside the house and have no idea where it is buried I thought I was doing the right thing. I don't actually need to do this. I guess I was being a bit on the safe side. I think I have convinced myself to put 2 small plastic garage type units in the cupboard with 2 100 A switches. One of the cables is a 2 core with a brass sheath used as a neutral. I have used heatshrink and tape to make a neat job and it is enclosed but I'm not sure I like this type of wiring Looks like SWA single core but it's not It's copper wire armoured (if there is such a thing) Perhaps someone can enlighten me.
It's going to have to be listed as a departure with recomendation to changing the stuff. It's been there for 40 odd years though.... And otherwise looks sound where I can see it.
Yes you heard me right the mains is in a barn about 60M away lol. 4 25mm tails 2 for the main and 2 the same colour for the off peak. Now perhaps you can see why I cut the off peak wire thinking they were unused (It only became apparent when I went to the barn and saw the off peak meter) Thankfully I left the tails long. Moral of the story. If you don't think something is being used leave the bloody wires as long as possible and tie them out of the way INSULATED. Thankfully I did.

 

[Guitarist]

I admire you for tackling this. It is impossible for us to really comment on what you are up against, but from what you have described so far I think I would have offered 2 options regarding this setup.

1) New install to my design
2) Walk away.

Best of luck

 

[Engineer54]

One of the cables is a 2 core with a brass sheath used as a neutral.

Brass sheath?? Never seen or heard of such a cable system!!! Going purely on what you have written it sounds more like MICC, but illegally having the sheath used as the neutral conductor!! Almost like concentric wiring, but with a twist!! lol!! I would look into this cable configuration a lot deeper than you have, this sounds like a potential major cock-up waiting quietly to Bite!!!

 

[londonlec]

Ive only skimmed over this but it looks like a bad design by someone.

 

[Dan the spark]

Are these 25mm tails your describing coming into the house double insulated tails or are they an swa?

 

[James Warren]

The tails (4 in total ) are in swa. This part look like it was done by the distributor but why they put the meters in an out house god only knows. Like I said it looks like it has been there at least 30-40 years.
It has to be the most bizare set up around.

 

[RISElectrical]

The brass sheath you spoke about does sound like pyro (micc) which if it is an the sheath is used as a neutral then that is a problem which needs addressing. Can you post a picture up of this cable? I assume this then has a separate cpc wired with it? Good luck. Sounds as though you'll need it. Personally I'd have insisted a full EICR be carried out prior to any work and then quoted accordingly. As said in a previous post, certain items would need upgrading to my design or I'd also walk away.