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:

 

[truckster]

The original install could be using the armour for the earthing, check the CU in the house for a connection between armour and earth or maybe earthing via the copper pipe which is non compliant. If that pipe is unused you could get rid of it completely or you will need to bond it either to the house CU with 10mm or TT the garage board and then you could bond it to that. Thats a budget constraint, how far is the garage from the house?

 

[srl-8]

The garage is detached and is approx 25 meters from the main house DB .

So If i prove that the armor is used as the earth, does that mean i would connect the steal armor wires to the earth block in the new garage Cu ?

Failing that, is a earth rod for the garage Cu acceptable ?

Cheers

 

[GLENNSPARK]

Rodding the garage(tt) is to get round the exported earth thing. What type of earthing arrangements does the house supply have?

 

[GLENNSPARK]

Theres a thread on here just for exported pme...check it out mate.....

 

[telectrix]

you need to get Zdb at the garage CU with that lead to the pipe disconnected.( assuming the SWA armour is used.). no need for RCD in garage unless you feed the SWA independently of the house RCD. As you will be using a plastic CU, you will need to fit a banjo to the SWA gland and lug a fly lead off to your earth terminal.

 

[srl-8]

The earthing looks to be TN-C-S.

If i cannot proove that the SWA is connected to earth, is it best practice to use throw in a earthing rod for the garage cu.

 

[malcolmsanford]

It is not that hard to prove that you have an earth from the house to the garage. With a wander lead do an R2 test from the MET to the garage SWA.

 

[GLENNSPARK]

Either through the rcd at the house board or rcd at the garage not both as you want discrimination: you could run it of a breaker at the house supply and rcd it at the garage board. this way if it trips you dont have to go all the way back to the house to reset it and dont forget if something in the garage trips the rcd in the house board.....you will lose all circuits fed through that rcd......

 

[telectrix]

or R1+R2, with the SWA dissed. and L/armour shorted at 1 end.

 

[srl-8]

Thanks guys,

So to confirm, The Main house DB is RCD protected. So you are saying that there is no need to fit a RCD cu at the garage end?

If I can prove the earth is attached to the house MET via the armor, then I just use a banjo glad and fly lead as mentioned above and connect to the Garage MET.

If no earth returns to the house , then a earth rod would be suitable...

Sound ok ??

 

[truckster]

The earthing looks to be TN-C-S.

If i cannot proove that the SWA is connected to earth, is it best practice to use throw in a earthing rod for the garage cu.

The armour must be connected to earth at the house end whether it's the earthing or not to provide protection.

My preference for remote buildings is a TT system but you would have to ensure that the armour and gland are inaccessible in the garage, I do this by using a PVC gland and cleating the cable tightly underneath it.

 

[telectrix]

Thanks guys,

So to confirm, The Main house DB is RCD protected. So you are saying that there is no need to fit a RCD cu at the garage end?

If I can prove the earth is attached to the house MET via the armor, then I just use a banjo glad and fly lead as mentioned above and connect to the Garage MET.

If no earth returns to the house , then a earth rod would be suitable...

Sound ok ??

sounds good to me. best practice would be to have the RCD at the garage end so as a fault in the garage will not affect the house installation. this , however would mean feeding the SWA independent of the house RCD, as you don't want 2 RCDs on the same circuit. either one or both will trip in the event of a fault.

 

[GLENNSPARK]

Pointed this out earlier tel....Better in the garage methinks too........

 

[Engineer54]

The earthing looks to be TN-C-S.

If i cannot proove that the SWA is connected to earth, is it best practice to use throw in a earthing rod for the garage cu.

You don't seem too sure what the earthing arrangement is in your house, ...As your still training, ...Be ''SURE'' what arrangement you have, before you start any work on your garage!!!

A. TN-S Earthing normally taken directly from the DNO cables armoring/lead sheath into the MET.

B. TNC-S earthing normally derived from DNOs neutral conductor at the cut out box, then into the MET.

C. TT earthing normally via a a separate earth conductor directly into the MET. (often disappearing without trace, and often with no earth rod pit in the garden)

 

[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.