Difficult Service head

[Lorzor]

Hello all,

I've recently put a new circuit in a house and when filling out my EIC, I needed to access the service head (attached).

I'm relatively new to this and I'm struggling here.

In order to access ANY part of this, you have to pull the main fuse and I had to cut a few metal tallys off. As you can see on the left is where the main fuse sits, to the right there is a cover for the MET and underneath is a cover for the incoming cables. The black box between the meter and thefuse housing is not removable - I can't see where the main earth is. The earth cable you can see is bonding from the gas pipe.

Also, immediately I thought it was a TNS system but it gets quite strange. The what looks like SWA is not SWA, it looks and feels like copper!! IT DEFINITELY isn't steel. Additionally, I can't find a neutral anywhere, I can't see if it is in with the red incoming wire but I'd be pretty surprised if it was.

Could the copper SWA (I know) actually be the PME neutral and we are actually looking at a TNCS system here?

Either way, I have never seen anything like this cable before.

Thanks in advance, I genuinely don't know if I'm just being stupid or inexperienced here but I'm kinda stuck with a way ahead.

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[7029 dave]

WHAT THE HELL ARE YOU DOING!.? Report that ASAP, That is all I am going to say.

 

[sparksburnout]

WHAT THE HELL ARE YOU DOING!.? Report that ASAP, That is all I am going to say.

I was hoping Dave didn't notice.......

 

[Wilko]

Sharp intake of breath I suspect ...

 

[Lorzor]

Had a quick scan of the whole thread and cannot understand what the hell is going on here ??? The service head is a TNCS system with a concentric cable which has a LIVE red conductor and a unsheathed armouring which is a combined neutral/earth. You shouldn't be dismantling the cutout to look at connections. With 600a plus fuses protecting the cut out it is dangerous to mess or tamper with it. It looks like you have removed the bottom cable cover which exposes the cable armouring.

you can measure the loop impedance and can determine what earthing type you have from that. If the earth cable terminates in the side of the cut out the majority of the time it is PME (there are some cases that there is a link that has been removed inside the cutout but most of the time you can see the Earth connection of a TNS system sweated to the outside of the cable head.

or am I missing something.......

Before I removed the covers, you couldn't see ANY of that. It was just a bunch of black boxes. I couldn't see the cable armouring(which isn't armour, its copper), I couldn't see the MET, I couldn't see the main earth. The one in the picture is the gas bond.

Because I couldn't see the MET or any earth cabling - I didn't know if it was TNCS or TNS for sure. Infact, at one point, due to the nature of the equipment it was suggested it may actually be TT but it isn't as the Ze is only 0.11 ohms.

So this is a TNCS system with an MET that can only be viewed or accessed by removing the main fuse. I have since learnt that I shouldn't have removed the covers and I'm getting it sorted with the suppliers. Lesson Learnt.

 

[sparksburnout]

Sharp intake of breath I suspect ...

Maybe he could put some seals in the post..

 

[Pete999]

Maybe he could put some seals in the post..

I still got my SWEB sealing kit

 

[Sparkie30]

Hi dude,the world won't end,and we have all done madder things...just don't talk about it,and provide pictures.
The original information you seek,may have been found with a phone call.

What type of property is it?

Do some deleting,have a think,and come back to us.

@ best reply to your issue pal.

Also ignore some of the replies because im they are perfect and have been been perfect since day 1.

Good luck

 

[Wilko]

So this is a TNCS system with an MET that can only be viewed or accessed by removing the main fuse. I have since learnt that I shouldn't have removed the covers.

Hi - I think this is not the MET. It is DNO infra, which is why it was inaccessible to you. The site might not be wired correctly and may not have a MET (if so you should create one).

 

[westward10]

Aside from the fact you deconstructed the head if that is definitely the gas bond it begs the question what is providing the earth. The MET can be in your dist board by the way.

 

[hightower]

Can you share a photo of the inside of the board?

 

[GMES]

@Lorzor I have deleted the images in your opening post for obvious reasons.

 

[Octopus]

@Lorzor I have deleted the images in your opening post for obvious reasons.

I've just read this whole thread hoping to see them.....................

 

[Dave OCD]

I've just read this whole thread hoping to see them.....................

Me too !

 

[Lorzor]

Oh man, you really missed out. I'm the ultimate badass!

 

[Richard Burns]

Looking at the service head on arrival I would have assumed a (slightly odd) TNCS arrangement.
The earthing conductor (even though in this case it is a gas bond) cable would not normally exit at that point, but no reason for it not to do so.
On measuring Zs at the consumer unit and getting a 0.11 ohm reading I would initially assume I was correct.
On attempting to measure Ze and checking the bonding arrangements I would then have been confused on finding the conductor from the service head was solely terminated onto the metal gas pipe.
On removing this conductor from the gas bond (and disconnecting the other bonding) I would then expect the Ze reading to be significantly higher since I would expect that the gas pipe was being used as the means of connecting the means of earthing to the installation (not permitted).

Because you have disconnected the bonding and got a Ze reading of 0.11 ohms there must be another means of earthing the installation, either the conductor from the service head is split in two at some point and goes off to the consumer unit and to the gas or there is another unseen conductor earthing the consumer unit.
If there are any other 6-16mm² green and yellow conductors in the consumer unit, that are not identified bonding, then I would be attempting to trace where they go and see if there is another reason for the low impedance.

 

[Lorzor]

Looking at the service head on arrival I would have assumed a (slightly odd) TNCS arrangement.
The earthing conductor (even though in this case it is a gas bond) cable would not normally exit at that point, but no reason for it not to do so.
On measuring Zs at the consumer unit and getting a 0.11 ohm reading I would initially assume I was correct.
On attempting to measure Ze and checking the bonding arrangements I would then have been confused on finding the conductor from the service head was solely terminated onto the metal gas pipe.
On removing this conductor from the gas bond (and disconnecting the other bonding) I would then expect the Ze reading to be significantly higher since I would expect that the gas pipe was being used as the means of connecting the means of earthing to the installation (not permitted).

Because you have disconnected the bonding and got a Ze reading of 0.11 ohms there must be another means of earthing the installation, either the conductor from the service head is split in two at some point and goes off to the consumer unit and to the gas or there is another unseen conductor earthing the consumer unit.
If there are any other 6-16mm² green and yellow conductors in the consumer unit, that are not identified bonding, then I would be attempting to trace where they go and see if there is another reason for the low impedance.

That was my guess, I'm going to attempt to find another method of earthing. It seems there may be quite a large cavity behind that service head, so it may be behind there. Don't worry, I won't dismantle it to get behind!

 

[weevilward]

Is the house semi-detached or maybe terraced? I've been in a semi detached TT house with Ze (measured through the rod, main earth disconnected from CU) of 100ish ohms, but Ze measured at the CU with everything connected it was right down to 0.20 ish. Next door had been converted to PME and there was a metallic path between the properties, I think through the plumbing systems, boiler CPC etc. So even with the means of earthing disconnected in this house, it appeared that Ze was stil 0.20 ohms.

 

[weevilward]

It might be that your place isn't actually earthed, but appears to be earthed from an adjoining property?

 

[weevilward]

P.S. I didn't see the OP photos so might be barking up the wrong tree...