Gotta get an earth

[SparkJ]

I have been asked to quote for the installation of four brick lights in the wall adjacent to the front of a detached brick garage together with an external blue three pin caravan socket to the outside wall of the garage.

The garage has an old semi enclosed fuse Wylex CU already installed which only has one circuit installed - a lighting circuit with four conventional batten lights inside the garage. The garage is 15m distant from the house. The Wylex CU is connected to the main house CU via a two core 2.5mm armoured cable connected to a 30A wired fuse. As far as I can see the armouring is not connected to anything at either end.

There is no water/ gas services at the garage although there is a great big RSJ holding up the roof.

The house has a TT earthing system with an old style consumer unit with wired fuses. It is buried at the back of a cupboard in the kitchen and is hard to get to and has no space around it.

I have not been able to get any Zs reading from the lighting circuit in the garage so I am assuming that there is no earth of any sort.

What I am proposing is to rip out the Wylex CU in the garage and replace it with a two way garage unit with a built in 30ma RCD and extend the lighting circuit to incorporate the brick lights and bang in an extra radial circuit for the caravan circuit.

Also to replace the 30A wired fuse in the house CU serving the armoured cable with a screw in 20A MCB conversion jobbie.

I would appreciate your input on the following:-

Should I install an earth rod at the garage with a 10mm earth cable connected to the garage CU

Is the RSJ in the garage considered

 

[binky]

Sounds good to me. RSJ is fine as it is not in earth contact. SWA shouds be earthed at house end, but not garage - see thread on exporting earths. 6mm bond to earth rod is fine for TT 10mm is better, use what you got! Is SWA buried between house and garage? if so should really be RCD protected in line with new regs if less than 50mm deep in wall or ground. Isolators not required, but no harm in fitting at house end if you desire.

 

[betty swollocks]

i agree with binky..

i'm always of the opinion that so long as you leave the property in a safer condition than it was before you began you've covered yourself.

i personally would quote to rcd the swa from the house but leave that option to the customer, if he wants it doing price it accordingly for the trouble, it sounds like you're gonna struggle with space around the old wylex in the cupboard.

the rest of your plan sounds good to me, by fitting the rcd and rod in the garage you've improved the existing installation and covered your own job as well,

 

[SparkJ]

Thanks for your comments.

With respect to the RSJ bonding do I understand correctly that it should not be bonded as is is not in direct contact with the ground?

 

[batty]

J first thing to check is earth fault loop in house. Then you can decide if an Rcd is needed house end if there is not one.

Batty

 

[batty]

Thanks for your comments.With respect to the RSJ bonding do I understand correctly that it should not be bonded as is is not in direct contact with the ground?

If cables could come into contact with it I would if not then don't bother.

Batty

 

[great68]

Sounds good to me. RSJ is fine as it is not in earth contact. SWA shouds be earthed at house end, but not garage - see thread on exporting earths. 6mm bond to earth rod is fine for TT 10mm is better, use what you got! Is SWA buried between house and garage? if so should really be RCD protected in line with new regs if less than 50mm deep in wall or ground. Isolators not required, but no harm in fitting at house end if you desire.

I dont agree with all of this.

The SWA should be earthed at the supply end. This means it does not need 'RCD protection in line with the new regs if less than 50mm deep in wall or ground' Putting that aside my views are an RCD in this type of situation should be at the garage/shed/outbuilding end.

 

[green-hornet]

I would like to break this down into the main principles if I can.

The earthing arrangements must be in place throughout the installation.

For instance any cable exiting a db should be earthed at origin, therefore the cable supplied to the garage should be earthed at the origin ie the house.

The earthing arrangements at the garage could be improved by installing another rod, this could be linked via the armour to the main earthing for the house, the benefits are that two rods are better than one.

You must be able to work and test on any part of the installation, so the fact that the cu in the kitchen is hard if not impossible to get to should in my opinion require a re siting.

If you bond water and gas at origin there is no requirement for bonding from the garage back to the house to gas and water, after all it is just a db.

The rsj would not require bonding,

Exporting an earth is not an issue with TT systems its only a problem with pme for obvious reasons.

An isolator is not required but could be a good idea for when the property is left empty for holidays etc leaving a circuit dead whilst away is always a good idea.

Remember that all TT systems will require RCD protection.

 

[sarni31]

you might find 708.55 of Regs usefull for caravan socket

 

[a1]

Earth the Armouring at the House end.

Terminate into a plastic CU. If not a plastic CU - then Terminate it into one of these. (placed directly under the CU).

Take your Phase and Neutral into the CU.

Bang in a rod, test and job done.

 

[ianmacd]

Why isolate? If both ends are TT then there is no problem or am I missing something? TNCS, now thats another story.

 

[batty]

Why isolate? If both ends are TT then there is no problem or am I missing something? TNCS, now thats another story.

I tend to keep seperate buildings seperate. On a TT I would put TD Rcd house end and 30mA Rcd shed end for discrimination. Would cost a little more on a job but I would allow it in my price.

Batty

 

[Oracle]

Many different ways to skin a cat (call Apache quick!) - As there are many ways to interprete the regs!

O.

 

[a1]

Many different ways to skin a cat (call Apache quick!) - As there are many ways to interprete the regs!O.

I hope Janice doesn't see that.

 

[SparkJ]

Thank you all for your input.

Exporting earths was a topic that I remember being raised many times on my Inspection and Testing course. Sadly all we students ever got in reply was evasive answers or no answers at all or

 

[sarni31]

REGS 542.1.8

Where a number of installations have seperate earthing arrangements, any protective conductors common to any of these installations shall either be capable of carrying the maximum fault current likely to flow through them...

So if you earth the SWA at both ends your new earth conductor/rod have to be able to withstand the whole installation fault currents....

or be earthed within one installation only and insulated from the earthing arrangements of any other installation,

IF THE PROTECTIVE CONDUCTOR FORMS PART OF A CABLE ,

the protective conductor shall be earthed only in the installation containing the associated protective device ...

Hope this helps clarify Guiness Drink

 

[steptoe]

TT system, so here is my shot at the scenario,

earth the SWA at BOTH ends,

there must be RCD protection for ANY circuit you modify (this will be the SWA, so MUST be RCD'd at house end)

the RSJ MUST be earthed, (it doesnt float in mid air so MUST be in contact with the general mass of earth somehow, unless the garage is PVC)

an additional rod at garage end would be benificial, tho depending on your Z readings not perhaps necessary.

hope to be of some help,

Albert

 

[sarni31]

TT system, so here is my shot at the scenario,earth the SWA at BOTH ends,

there must be RCD protection for ANY circuit you modify (this will be the SWA, so MUST be RCD'd at house end)

the RSJ MUST be earthed, (it doesnt float in mid air so MUST be in contact with the general mass of earth somehow, unless the garage is PVC)

an additional rod at garage end would be benificial, tho depending on your Z readings not perhaps necessary.

hope to be of some help,

Albert

Arn't garages made out out of bricks, giving very high resistance to earth..

therefore no potential and no need to bond the rsj .. ?:|

 

[steptoe]

structural metalwork MUST be bonded,

unless you wish to deviate from the big red comic,

I dont make the regs, thats probably why I dont always follow them, but Im not going to give advice to someone else to deviate unless they can justify their reason, hence they prob wouldnt be asking in the first place.

after all, a bit of 10mm from garage CU to the RSJ isnt going to be that much hassle really anyway, is it?

 

[sarni31]

structural metal work that is bolted to the floor and forms the main structure of the building yes.... because its bolted/embedded to the floor and therefore in contact with earth...

rsj's, steel windowframes, metal sinks, baths.... no

Of course... I could be wrong Guiness Drink