Earth from cutout to MET - who is responsible?

[jg321]

Hi all,

Something that's been bugging me for a while but never got around to looking into. The earth from my cutout to the MET seems very small. I'd guess at 2.5mm - it's solid core, not stranded. I've attached a picture. Supply is TN-S fed by split con (confirmed when a contractor came to fit an isolator for me), which appears to be daisy chained from next door (it heads under the floor to the other side of the house which is where my neighbours are attached).

The contractor never mentioned the earth, and didn't seem to even know what TN-S was when I asked him (I had to rephrase it and ask him if the link between neutral and earth was present in the cutout). I didn't want to ask any more questions after this.

Therefore I have two questions:

1) Is the earth between the cutout and MET undersized? Fuse in cutout is 100Amp (confirmed by the contractor).
2) If is is undersized, who is responsible for replacing it? As you'd need to break the seals in order to change it, I'd guess the DNO are responsible.

Thanks in advance for any replies.

Jon

 

[EFLImpudence]

It certainly appears to be undersized, although it might be alright if it really is still TN-S.
A lot have been made PME even though appears as TN-S in the premises.

The DNO is indeed responsible.

 

[ban-all-sheds]

IThe DNO is indeed responsible.

I don't think so.

That earth block is not theirs.

(4) Unless he can reasonably conclude that it is inappropriate for reasons of safety, a distributor shall, when providing a new connection at low voltage, make available his supply neutral conductor or, if appropriate, the protective conductor of his network for connection to the protective conductor of the consumer’s installation.

There it is:

That's where their responsibility ends.

 

[jg321]

That makes sense BAS, but that terminal can’t be accessed without breaking their seals and removing their fuse, so surely they need to be involved in order to access those terminals?

 

[EFLImpudence]

It would have been quite simple to have a couple of holes for a screwdriver.

Is this a knock-out?

Do you consider a lead sheath to be the same?

 

[plugwash]

That makes sense BAS, but that terminal can’t be accessed without breaking their seals and removing their fuse, so surely they need to be involved in order to access those terminals?

Sure but the same is true of the output terminals on most meters (which AIUI are the usual demarcation point for the current-carrying conductors).

 

[jg321]

Thanks EFLI - hadn't spotted that. I'll take a look.

@plugwash true enough. A more sensible design where the demarc could be accessed would be much better, although with isolator switches we now have this in some cases.

 

[ban-all-sheds]

They may well not have used one here, but I'm sure there are cutouts on the market where the earth terminal is not sealed.

 

[ban-all-sheds]

IDo you consider a lead sheath to be the same?

A lead sheath is different - they would have to take the sweated cable to an earth block to provide access to it.

 

[EFLImpudence]

The instruction says nothing about providing access; merely make available.

Although, I suspect the DNOs don't really care.

 

[JohnW2]

... A more sensible design where the demarc could be accessed would be much better, although with isolator switches we now have this in some cases.

I seem to have experienced a half-way house. When I had an isolator fitted a couple of years ago, the guy put 'standard proper seals' on the access to the incoming tails, but also put Mickey Mouse plastic seals on the cover over the outgoing connections. When I asked why he had done that, he said "your electrician can cut those plastic ones if necessary".

I can't make a lot of sense of any of that. The plastic seal is, I suppose, a gesture to discourage 'DIY tampering', but I don't see why there is a need for a 'proper seal' on the incoming side of the isolator, given that it is downstream of the meter. After all, in the absence of an isolator those tails would usually go to a CU, access to which would certainly not be prevented by DNO/supplier seals.

Kind Regards, John

 

[ban-all-sheds]

The instruction says nothing about providing access; merely make available.

You cannot have made something available for connection to if you have not made it accessible to connect to.

 

[EFLImpudence]

You can if you wish to limit those who may make the connection.

 

[JohnD]

an isolator fitted a couple of years ago, the guy put 'standard proper seals' on the access to the incoming tails, but also put Mickey Mouse plastic seals on the cover over the outgoing connections. When I asked why he had done that, he said "your electrician can cut those plastic ones if necessary".

If the isolator is downstream of the meter, there have been for a long time isolators where the outgoing terminals can easily be exposed and accessed. If we assume that a competent person is doing it, he will have turned the isolator off first and tested for dead. I remember the old MEM 100A isolator enclosures had a removable "hatch" over the load side terminals for that very reason. Quite sensible.

View media item 820
I've seen similar arrangements on other brands of enclosure.

The supply side terminals will always be live unless the company fuse has been removed.

 

[JohnW2]

If the isolator is downstream of the meter, there have been for a long time isolators where the outgoing terminals can easily be exposed and accessed. ... I remember the old MEM 100A isolator enclosures had a removable "hatch" over the load side terminals for that very reason.

Indeed - just like mine, give or take the plastic 'seal' which has been attached to the cover (c.f. your 'hatch') over (just) the load-side terminals.

If we assume that a competent person is doing it, he will have turned the isolator off first and tested for dead. I remember the old MEM 100A isolator enclosures had a removable "hatch" over the load side terminals for that very reason. Quite sensible. The supply side terminals will always be live unless the company fuse has been removed.

All true - but, as I said, in the absence of the isolator those tails would usually have gone straight to the Main Switch of a CU, access to which would obviously not have been prevented by a DNO/supplier seal - so why those seals if the ends of the tails are connected to the supply-side of an external isolator, when they wouldn't (couldn't) exist if they were connected to the supply-side of an isolator (Main Switch) within a CU?

Kind Regards, John