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Topic Title: Mineral Insulated incomer
Topic Summary: earthing arrangement?
Created On: 26 October 2010 10:02 PM
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 26 October 2010 10:02 PM
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Zs

Posts: 2843
Joined: 20 July 2006

hello, ah, so you don't have BBC4 either?

I did a PIR today which is a massive fail on many counts but I could do with some help on the supply/earthing arrangements please.

A Flat. Built in 1962. Don't ask about protection, just think rubbish and nothing and you're in that flat.

Incoming supply is what I would call MIMS. A copper tube with the two conductors inside it, embedded in powder. I know that others use other names for it.

This is connected with a brass gland to a small white MEM box with a screw on hinged lid. Metal.

Inside this little cupboard the main 60A BS88 fuse , in a porcelaine fuse carrier and a black bakelite connection for the neutral. I've a notion that the neutral was also fused but didn't look inside.

From there, cloth covered tails to meter and then to the old wylex re-wirable 8 way board. A tinned copper, bare earthing conductor, about 10mm CSA is connected to the housing of the MEM box to the earth bar in the fuse board.

Then, taking you back to the beginning of the incomer again, just where it enters the flat and before the MEM main fuse there is a 10mm green and yellow which looks about 10 years old or so, attached with a bonding clamp to the copper of the incomer and connected to the water stop cock.

I thought I was looking at one of the systems where the water pipes were used as earth. But, test results..... brace yourself.

Ze from the DB with the water bonding thing in place 642 ohms.

Ze without the water bonding thing in place 741 ohms

Zs from a socket in the kitchen 0.35

Zs from immersion heater 0.38

Oh my giddy aunt. Bearing in mind no gas bonding and no CPC on 2 x lighting circuits. Where's that going? Good job we test from the DB and not only from internal connections.

My questions:

1) What earthing arrangement was used for MIMS incomers and what should I be seeing there in terms of connections etc.

That's kind of like a TT isn't it, with the neutral conductor insulated from the copper tube by the powder?

2) Is this a supply authority issue?

I think so. Big time. I only hesitate to do that because of the debacle over that house with the dodgy shower and my subsequent telling off by the guy from the DNO for scaring the client.


But I must take action on this so any help would be appreciated.

Thank you

Zs
 26 October 2010 10:19 PM
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peteTLM

Posts: 3137
Joined: 31 March 2005

The MICC cable is just a submain from the actual DNO cutout hidden elsewhere. Have a look if you can, probably near the front door or in another ground floor flat.
The copper tube sheath is the main earth, but by all accounts this probably isnt connected to anything meaningful at the cutout end.
Micc is usually glanded into a metal enclosure, but its not unusual to see it with just the cable pot on, and some sort of clamp providing the connection to the sheath.

Pre-privatisation, this would have been a DNO issue. Post privatisation, all parties will wash their hands of it, and call it a 'landlords riser'. The freeholders will have to carry the can 9 times out of 10.

P

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Lack of planning on your part doesn't make it an emergency on mine....

Every man has to know his limitations- Dirty Harry
 26 October 2010 10:22 PM
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normcall

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Sounds like typical sub-main used in flats.
eg CNT used to provide bog standard cutout in central position and MICC sub mains to all the flats or offices.
In Hemel, in Bank Court, the offices over the shops had a MICC sub main and meter to each office - the the EEB moved in and used them as their offices, so they all were linked together as naturally they didn't pay themselves for the electricity supply. When they moved out into purpose built offices in Whiteleaf Road, we had to go and unravel all the linked supplies and install a meter into every room.
Then it all got changed again as new tenants moved in and took several rooms!
Remember also that 951 clamps were not thought off, so strip copper with holes in and ye old nut and bolt connected the earth (if lucky) to the outer sheath. Over time it loosens and falls to bits.
Find the cupboard with the unmetered supply and I bet it starts as TNS 1950/60's

You didn't listen at the church a while ago did you. Magnesium Oxide is the 'white powdered stuff' - lover of moisture! The 'glands you describe where the sort used in the special MICC boxes so it just clamped the pot and no need for a 3/4 brass gland - real rubbish!

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Norman
 26 October 2010 10:27 PM
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John Peckham

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Without seeing the other end of the cable you cannot say what sort of earthing system, if any, you may have.

The cable is nowdays known as MIMS which used to be called Pyro, MICC.

I have seen pleanty of these arangments in flats. The cable is usually a 2H10 or imperial equivalent. This a heavy duty copper sheath with 2 No 10mm cores. The copper sheath is usualy used as a CPC and the gland or sealed pot is terminated in the metal board providing the earth. I thing I know the MEM enclosure you have mentioned. It is cream coloured and if before the meter the door can be sealed by the DNO.

Your install being before 1966 may use the water pipe as an earth. It could be the water main has been replaced by a plastic pipe and the earth has been lost.

The debate may be who owns the distribution circuit. The landlord,premises owner or the DNO.

I don't understand how you are getting triple digit Ze figures with the bonding connected or disconected but you are getting a low Zs?

Try doing a loop test with the green clip on the copper sheath. If you get a crap reading then it could be the sheath is not earthed at the supply end. If you get a good reading on the sheath then you might have a bad joint at the supply fuse board or the bare earth to the board.

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John Peckham

http://www.astutetechnicalservices.co.uk/
 26 October 2010 10:59 PM
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Zs

Posts: 2843
Joined: 20 July 2006

Interesting. And beginning to sound horribly time consuming.

These flats aren't in a big block with communal acess but each has their own front door accessible from outdoors. Albeit some by a small staircase. However, I'll go and have a look round and ask about service management. We certainly have some flats round here with what you have described (orange covered MIMS round the outside of the buildings) so could be, and thank you for suggesting that.

Were I short of work I'd pop a letter through every door and suggest a check-up. South Bucks if you're looking for work

I'll run the extra Ze test as soon as I get back there. Was hoping just to go back in order to present the reports but this looks like a bit more to do.

Thank you. And Norm, believe me I was listening. You said it was talcum powder. Ever since then I've held my finger on the button of a failed IR test on MIMS for a bit longer and watched the number rise. Or wasn't I supposed to tell everybody you taught me that?

Back soon...........gone fishing
(for earth connections).

Zs
 26 October 2010 11:13 PM
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John Peckham

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Zs

Have a look in the landlords supply cupboard. You may find a Ryfield or GEC type board or something horific. That may answer the question of the earthing system and if your MICC is conected to it.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 31 October 2010 03:07 PM
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Zs

Posts: 2843
Joined: 20 July 2006

a'ternoon.

I am now totally disconfluk(e)ulated. I've just been over to the flats to present the reports. She wasn't in. Grrr.

However, I took the opportunity to look for what you suggested.

There is no common area cupboard, I promise you that every bit of wall around that building is part of a flat. No little wooden doors or cupboards, no cellar etc.

On one side Every one has it's own gas box on the outside wall. Those are the ones with a front door at ground level.

On the other side some have a gas box on the outside wall but not all. Those are the ones where you have to go up a few steps to get to the front door.

Not a single electricity box to be seen. My client has her meter indoors and it looks like it has been there since it was built.

How far away from the building could such a common supply be? I cased the joint properly. There are two big wooden sheds in the gardens with padlocks on but to be honest, they look like your shed and my shed, not a supply building and certainly no danger notices.

Another owner at her dustbin told me they don't have one but that's not necessarily reliable.

MIMS supply from where then? the end of the street?

How to proceed other than just present fail reports and leave her to get on with it? Which I am a tad inclined to do.

Zs
 31 October 2010 03:51 PM
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John Peckham

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It has to be there somewhere Zs. I assume there is lighting in the common areas? Who does the maintenance? Is there a caretaker who changes the lamps sets the stair lighting time switch etc? That is where the landlord suply wil be with the service cable head. Often they are protected behind looked doors stop user re-connection of the supply after it has been cut off.

As Pete TLM will veify we found distribution fuses recently in a very posh flat that fed other flats. That was in boiler cupboard at high level inside a flat that the owner did not know was there.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 31 October 2010 06:25 PM
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slittle

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Under the stairs is a favourite place for the cutout. There's loads like that around the less rural parts of my patch.

The low zs's could be a neutral fault somewhere on the customer's side (assuming you've not IR'd it yet)

I have to admit I haven't read the whole thread as the kids and wife have gone trick and treating and left me with the pleasure of passing ghosties !


Stu
 01 November 2010 08:25 AM
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Zs

Posts: 2843
Joined: 20 July 2006

Well, As far as I can see there is no common area other than the much tinkered with outdoors where they have all made their own garden, after a fashion. Each flat has its own front door leading to outside which could be a change from how they were built. The steps look in good condition all along the back row.

I did a global IR test phase and neutral to CPC only, and meter read 7 M. Then all circuits with a CPC individually, the low IR comes from the sockets at about 7.23M. No test on the lights x 2 as there is no CPC. I stopped testing at that point. You'll be pleased to know the shower is >500M.

I can see where the gas meter used to be, I couldn't find a new one. On the phone she says it is in the garden. Shame she wasn't in as agreed yesterday as it is going to be dark when I get there now.

I'm wondering if the new position for the gas meter is 'common' and they have TT'd them away from the flats at the new position? That would explain the path to earth for the Zs tests I suppose? They wouldn't have would they? Certainly no gas bond in the flat. Some supplementary though.

so I still haven't done what you suggested John. But will do. However, even if that shows a weakness in the earthing conductor it doesn't explain how this lot is earthed. So I guess I have to find the landlord......double grr.

Truly annoying at such a busy time. But I will let you know what is agreed. This was done for selling and the new buyer is going to have something to say. Hope to catch her this evening.



Zs
 01 November 2010 09:01 AM
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normcall

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And what did the electricity distributor (EDF?) say when you asked where their main incoming cable is?

-------------------------
Norman
 01 November 2010 12:38 PM
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OMS

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MIMS supply from where then? the end of the street?


As Norman suggested, you need to speak to the supplier - it's quite possible that the MICC's go back to an external "feeder pillar" (Lucy Oxford cast iron cabinet sort of thing) containing the incoming cable and the distribution fuses to each flat. Technically those MICC's would be part of the DNO network although thay will try to disown them.

Regards

OMS

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Failure is always an option
 01 November 2010 04:12 PM
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ArthurHall

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If the DNO cant be bothered looking at their own drawings, tell them you are going to excavate to install an earthing system, they then have an obligation to supply drawings of their plant in the area. That should give you a clue.
 01 November 2010 06:45 PM
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Zs

Posts: 2843
Joined: 20 July 2006

You guys are so brilliant. How do electricians cope without the use of a forum such as this?

Norm, I've not contacted EDF yet, on account of getting a right royal er, telling offocking from them recently for getting a customer to make an emergency callout for a bad Ze. I took it on board and I don't want to develop a reputation as a panic monger. Let's face it, I'm pretty easy to identify amongst sparkies round here. BC wouldn't be impressed and I think they trust me so I'm being careful.

Definitely no common area, confirmed by the client 10 mins ago. Going back tomorrow evening to run your test JP, by head lamp light.

To follow....... Test results by clipping the croc onto the MIMS and me telling you I put a strap of 16mm in...I hope. did this job on a price andd I need it to be finished.


But Alan or any other supply people out there, a question for you.. I'm finding a great deal of old and tired supplies. Given a good supply set up the electrician is in a position to carry out our work effectively. We are also in a position to give good advice on the installation and safety. Without a modern and efficient supply, right up to the meter, we are pretty well stuffed and even the most diligent of us can look like we are incapable.

Is there something I can show to my clients which tells them how they are entitled to a good and safe supply? Is there something I can leave with them so that they know who to call and what to say? Sadly, phoning a DNO is a time-eating occupation which I would rather reserve for my rocking chair days.

When I get to the old age people's home I'm gonna be phoning up DNOs for sport. But until then, What rules, what laws, what entitlements can I show to my clients with regard to DNO responsibilities? Please.

Zs
 02 November 2010 09:44 AM
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OMS

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When I get to the old age people's home I'm gonna be phoning up DNOs for sport. But until then, What rules, what laws, what entitlements can I show to my clients with regard to DNO responsibilities? Please.


LoL - I can think of better ways to grow old disgracefully than baiting the DNO's but there you go

I suggest you get a copy of ESQCR regulations to understand what DNO's are (and are not) required to do. From there see how your particular DNO have implemented ESQCR into thier working rules etc - thier website is a good starting point if you haven't cultivated a tame network engineer.

But Alan or any other supply people out there, a question for you.. I'm finding a great deal of old and tired supplies. Given a good supply set up the electrician is in a position to carry out our work effectively. We are also in a position to give good advice on the installation and safety. Without a modern and efficient supply, right up to the meter, we are pretty well stuffed and even the most diligent of us can look like we are incapable.


Tired and old doesn't always equate to "bad" - particularly when it comes to DNO services. In terms of safety, even old and dilapidated supplies comprising MICC or PILC are still cabable of giving a safe and secure supply to a domestic property - it's up to the spark at the scene to determine that the supply is fit for purpose (Reg 132.1 et seq) and if not to advise thier client accordingly.

Personally I would contact the DNO (via the client if need be) to ascertain how the service is being presented - or failing that RCD the system and march on.

Regards


OMS

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Failure is always an option
 02 November 2010 09:59 AM
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normcall

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Often 'others' do things to supplies.
During my year of a 'proper job' one of my thankless tasks was to 'find' lost supplies.
One was a lamp-post buried under a junction to a new estate - developer would have to pay to have it removed and that costs money!
Another was a demolished building at the foot of a hill not a million miles from Zs. Apparently (I'll talk to anyone), a lorry came down the hill about 15 years before I got involved, the brakes failed and it swerved into the building. The building was a write off and demolished. Under the rubble was found the live cutout and meter when investigated. Again, money would have been needed to sort it and it just got 'forgot'!

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Norman
 02 November 2010 10:12 AM
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OMS

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During my year of a 'proper job' one of my thankless tasks was to 'find' lost supplies.


Thankless no doubt - but searching for idle services was always good for overtime and bonus. You do find some incredible things though for sure. I'm sure it hasn't improved any of late

Regards

OMS

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Failure is always an option
 02 November 2010 10:42 PM
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Zs

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Well Norm, I'm wondering which hill. this flat is half way up a mega hill.

Anyway, Huge thanks to JP. albeit not straightforward running that test.

I'm pretty sure that my three lead tester makes a shrill sound if it cannot run the test it is being asked for. for example if the power is off when trying to run a Z test, or the earth croc is not connectected.

It didn't make a noise but it set about testing and tried for ages to bring back a result. eventually it came back with >2000 ohms. three times at different positions on the MIMS incomer.

So I got a bit of sandpaper and cleaned it up a bit.

1.03 ohms as a pure Ze. from the DB to the MIMS.

I put a strap of 16mm in between the connection to the MEM fuse holder box, with a lug on one end and a bonding clamp (I know) on the MIMS. I decided not to replace the whole earthing conductor so as to avoid messing around with the inside of the DB and being held responsible for anything in there. Not least, 16mm doesn't fit in the earth bar of those old wylex very well.

Ze 1.00 Zdb with the water bond back on 0.66. Still too high even if a TNS but I reckon I've covered my due diligence with that and a covering letter. That'll do for me for now.

She is adamant that there is no common area. The flats are leasehold but ground rent is £10 a year and there is no service charge. They are all privately owned.

One for you Norm, if ever you decide on that proper job again.

So, inconclusive with regard to my original question but the situation is much improved.

And I thank you.

Zs
 03 November 2010 06:49 AM
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normcall

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Hope it's not just below an underground station with the waterworks at the bottom. I worked on those when they were erected - grounds of a large house, if I remember correctly. Hill recently resurfaced due to my caravan having to weave from one side of the road to the other round the traffic islands and cameras to avoid holes deep enough to see Australia.
Do I have to check the memory banks?

-------------------------
Norman
 03 November 2010 10:50 AM
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Zs

Posts: 2843
Joined: 20 July 2006

Pretty much spot on Norm. Just a bit further up. Obviously something to look out for if working on flats in that area again.....the work of Norm and MIMS incomers buried in the footings. I bet you know Gavin too, he wired up alot of those houses in Broadlands avenue area. The ones I'm rewiring these days.

Zs
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