Change a old garage fuse board / Earthing question... pic s attached

[srl-8]

Hey,

I am looking to change a very old fuse box in my garage. I have attached pics for you all.
I am on route to becomeing a Domestic installer, and hoped i could get some more good advice if poss.

This old fuse box, is supplied from the main house Cu. It is on a 32A breaker. The Main Cu is protected by RCD.

The supply enters the garage from below ground in what looks like armoured cable. (see pic). I would like to change this to a small modern 3 or 4 way Cu, obiously with RCD. I will run a new radial & lighting circuit from the new Cu.

Question, I cannot identify a incomming earth ? All I can see is the Live and Neutral from the end of the Armoured Cable. Is this normal? The old metal box is earthed to a old copper pipe.. but cannot see a route back to the house main earth block?

What are my options here? Am I right to assume I either run a 10mm earth all the way from the garage back to the house Cu, Or install a earthing rod more local to the garage supply ?

I am still learning, so all advice or sugestions very welcome.

ps: Providing I am not running any large or abnormal loads from the garage, this supply from the house (on a 32a MCB) is suitable. I would only ever be plugging in the odd power tool, or running 2 light bulbs.. etc

Thanks!!


:stooge_curly:

 

[srl-8]

I have noticed the gas meter is actually only 2 meters from the new proposed installation. The gas has the 10mm cpc running back to the main MET in the house. Is it alright to connect to this from my new garage board earth.

I think this is, as I have identified a path back to the main earth block...?

 

[malcolmsanford]

no ................................... Unless you can confirm that a combined bonding and CPC conductor can take the fault currents that may occur during a fault.

 

[Deleted member 26818]

Yes....

 

[srl-8]

um.. spinlondon agreeing and saying yes...malcolm sanford say no??? can i get clarity on this.

 

[telectrix]

spinlondon is agreeing with malcolm, methinks.

 

[malcolmsanford]

You will have to confirm that the 10mm bonding conductor to the gas will be capable of carrying the fault currents of a combined Bonding/CPC conductor.

But you have what looks like a perfectly good SWA there, so as posted either do an R2 on the SWA armour or an R1+R2 and see what you have.

 

[telectrix]

i'd be inclined to rely on the armour for your main earthing and use the 10mm as an additional parallel main earth.

 

[Deleted member 26818]

No I am disagreeing with Malcolm.
There is no reason why a conductor cannot both be a CPC and a bonding conductor.
I would personaly rather use the armour as a CPC for the SWA, as that is what it is intended for.
However there is nothing preventing the use of a supplementary conductor, such as the gas bond.
I note from the pictures, that there is a copper pipe whith an earth connection.
What is this pipe for, and is it suitable to be used as a conductor?

 

[srl-8]

The old pipe is a disused/empty copper water pipe, that enters back into the main house. I would imagine, this is bonded at some point and also would offer a path back to to MET. ?? I can see that this was used as a bond at some point in the past.

??

 

[Deleted member 26818]

It appears you have a number of options, use the armour, use the gas bond (if the SWA conductors are 10mm²), use the old water pipe, or a combination of the three.
As there are extraneous-conductive-parts that are bonded back to the house MET, making the garage TT is not really an option.

 

[GLENNSPARK]

So what you meen is to extend the equepotential zone then spin?

 

[telectrix]

agreed. better than dissociating the garage from the house, as the zone is already extended by the 10mm cable and the disused water pipe.

 

[Deleted member 26818]

The fact that the old water pipe, the gas and the SWA are all earthed/bonded, would suggest that the equipotential zone is already extended, and judging from the pictures, has been for some time.
Attempting to isolate and separate the zone would IMHO be a nightmare.

 

[srl-8]

It looks like the live and neutral are about 2.5mm coming through the amor cable. what did you mean by..

"use the gas bond (if the SWA conductors are 10mm²), " ?

 

[telectrix]

you can't have undersized earthing and/or bonding conductors, but i've never known an installation not to comply with oversized ones.