main earthing

[islingtonmike]

Hi, I'm not an electrician but I employed a Part P quallfied one to install a consumer service unit and I wonder if the earthing is right.

I have a flat in a house which was first converted in about 1976. There's a Ryedale distribution box close to the entrance. The flat had a metal CSU served by an orange PVC coated copper core mineral insulated core - now understood to be Micc - with line and neutral. There is no earthing in this service cable.

My electrician had kittens when he found this out. "There's no bleedin' earth." He eventually decided to run a 15mm earth direct to a point on the Rydedale where there was also anchored a recent yellow and green cable on the assumption, I think in hindsight, that this would be properly main bonded.

The consumer unit was also 15mm earthed into the gas meter, service side as required. The water supply is in plastic although my central heating and water is in copper.

My question having thought about this for a couple of days and scooted around the site concerns the earthing. Isn't it absolutely near certain that the copper outer sheath is the CPC so that a connection should have been made on the gland asssembly - which is brass - by the attachment of one of those ringy thingys to the earthing rail on the CSU.

Otherwise, it is the case that I have been living in this flat for ten years and I could have been crispy noodle at any point.

A couple of other point. RCBOs have been installed across all the circuits. This means, does it not, that there is no reason to cross-bond the bathroom? This electrician told me this but then I wondered why if that was the case why he thought it necessary to cross-bond and earth the copper pipes below the combi.

cheers

 

[ColJack]

you mean the earth that's provided by the copper sheath of the MICC cable and should be taken off the gland with a banjo or similar?

the banjo ( coloquial term, called many things by many sparkies ) may not be needed if the paint was removed under the gland and locknut, or if the connection was proven sound to the metal CU..


a photo of the incomming cable from outside and inside the CU would give us a better idea of the condition of your earthing.

 

[Spark123]

A couple of other point. RCBOs have been installed across all the circuits. This means, does it not, that there is no reason to cross-bond the bathroom? This electrician told me this but then I wondered why if that was the case why he thought it necessary to cross-bond and earth the copper pipes below the combi.

cheers

RCD protection is one of the criteria which needs to be met for the omission of supplementary bonding in a bathroom. Other things do apply though, have a read here: //www.diynot.com/wiki/electrics:supbond17th
If the boiler instructions say that you have to cross bond the pipes then they must be done, there isn't a requirement in BS7671:2008 to do so.

 

[securespark]

The connection to the gas should not be on the service side...

 

[islingtonmike]

image of consumer unit. sorry I can't work out how to upload the image other than by this route.

//www.diynot.com/network/islingtonmike/albums/

 

[333rocky333]

Untitled

• islingtonmike
• 19 Jul 2009
• 2

one way is to Use the code by the picture, and copy it into the post.

 

[ColJack]

see where it says "show my images" under the reply window?
click that and then klick on the picture you want to include.. it puts the code in the text for it..

now..
is that a banjo i see on the inside? can't tell from that angle..

and what's with the fish eye look to the picture? did you use and endoscope?

edit: just had a closer look..
what the hell? the copper continues past the gland? that's not an MICC gland then? it's a compression gland.?
need a photo of the MICC cable where it's made off.. ( hopefully into a pot, otherwise the sparky wants a slap. )

 

[islingtonmike]

Coljack has potential as a forensic scientist.

You're right, there is no banjo there. The explanation is complicated. As I say the supply cable was simply detached from the 1976 installation and inserted into the new unit.

Unfortunately, the knock-out on the new unit was larger than that on the old unit. This meant that the gland unit could not grip on the new unit's casing. It was therefore decided to fabricate two washers which could be fitted either side of the unit's wall to secure the gland.

There was no banjo. I think this is because the electrician didn't consider the supply cable provided main earthing. I think that's its job. Could someone tell me definitely that this is the case. Or is to be determined?

Incidentally, the pot is some 200m along from the gland. The electrician didn't want to disturb because of an assumption that they're notoriously difficult to reset. It's made the box a bit too busy for my liking.

 

[Spark123]

The old imperial pots and glands are bad to get hold of, it is less brain taxing to try and dig out the old ones. As for stripping the MICC it isn't very difficult.
Seems to be a dying breed of electrician who can work with MI

 

[ColJack]

nasty stuff that's reported to give you cancer...
or at least the old potting compounds were...

 

[islingtonmike]

Coming back to the original question I had.

There should be a banjo on the gland which should be earthed into the earthing bank on the consumer unt. That is the case.

Finally, this may seem obvious, but the copper sheath of the supply cable is used as the main earth. Yes?

 

[rebuke]

Normally it would be - but without looking at the other end it's impossible to say for sure...

 

[Spark123]

The outer sheath of a MICC cable must be earthed - it is an exposed conductive part. Wether or not it is sufficiently sized for it to be suitable for use as an earthing conductor is another case.
Connection to the gland can be via a banjo, piranha nut etc.

 

[333rocky333]

That looks to me like a pyro gland, when it was done up years ago the olive would have squeezed up on the copper sheath, that is why he has had to leave it long like that, he would be unlikely to move the olive, without cutting it off.
He would then have to fit a new one and repot the thing,

It looks like the old trick of using SWA banjos so he can fit the gland into a larger than required hole or knock out.
I do not know anyone that uses banjos on pyro normally.