Earthing in a garage

[raustin]

Morning guys

Just want to check on the earthing for the garage that I'm working on.

Its a TN-C-S supply to the house.

The garage is detached from the house and is about 1 meter away. The supply is fed from a 16A MCB on a small CU with a 30mA RCD. The cable is run in SWA.

All cables and boxes are surface mounted and other than the socket, all boxes and switches are plastic.

The supply goes into the garage and connects into a metal clad double socket. From the double socket 2.5mm (no earth) is run into a FCU and from there 1.5mm (no earth) is run to a double light switch.

The lighting has the earths connected and just terminated in the back of the light switch, no earth going back to the FCU.

The FCU has the face plate and box connected with an earth.

No earth between the socket and FCU.

Metal clad socket doesn't have an earth between the box and the incoming supply.

What I have done is to re-wire from the double socket to the FCU with 2.5mm T&E. From the FCU I have re-wired to the light switch in 1.5mm T&E

I have also earthed the metal clad box.

I just wanted to check that this is all OK. I know that sometimes outbuilds shouldn't be conneted to the same earth as the house as they may be at a different potential.

Cheers

Rich

 

[Sidewinder]

Rich,

IF I understand your explanation correctly.

IF you are not exporting the earth then this must ocurr at the DB, in the remote building, then a rod must be connected to TT the whole remote install.

The cpc's in the final circuits must be connected back to this DB.

However, IF there are no extraneous parts in the outbuilding then you could carry out the PME earth if the DNO allow it.

I would issue an EDN on that as it will be doubtful you will achieve ADS.

 

[raustin]

Not sure I explained it right.

The garage installation is already in and being supplied from a small DB next to the main DB in the electric cupboard. There is about 1 meter between the house and garage which is connected with SWA cable.

There was an issue with one of the sockets not working which has now been resolved. The CPC from this socket is going back to the small DB. In the process I noticed that the lighting circuit CPC wasn't what I expected (although this is the first garage I've looked at)

The lighting CPC is not connected back to the DB, it is just termianted in the back of the light switch. Is this correct or not?

I also noticed that metal clad socket was not earthed to the CPC, again is this correct or not?

Cheers Rich

 

[Apache]

It's usual to 'park' the earth terminal in the plastic back box of a plastic light switch as there's no where to connect it [unlike a metal faced switch].

You mean that the socket had earth continuity back to the board but there was no fly lead to the metal back box? It is debatable whether that is required as the screws are earthed and should continue that to the back box AFAIK.

 

[raustin]

It's usual to 'park' the earth terminal in the plastic back box of a plastic light switch as there's no where to connect it [unlike a metal faced switch].You mean that the socket had earth continuity back to the board but there was no fly lead to the metal back box? It is debatable whether that is required as the screws are earthed and should continue that to the back box AFAIK.

I agree that the earths will be terminated in the box if there is nowhere for them to go ie metal front panel, but shouldn't they be connected back to the MET via the CPC?

I checked the screws, and there was no contunity between them and the CPC in the socket.

 

[Apache]

I'm lost. Did you take any pictures? How did you test continuity from CPC to screws?

 

[raustin]

I'm lost. Did you take any pictures? How did you test continuity from CPC to screws?

Sorry no pics - didn't think about it.

Tested continuity using MFT on continuity setting. Checked between screws holding the front plate on and incoming CPC, no continuity so in the event of a fault no earth path.

Connected back box to the CPC. Now when testing there is continuity between the screws and CPC and the case and CPC.

 

[SPECIAL LOCATION]

Are you saying the socket & light were wired in twin cable with NO earth at all!?

And are you then asking if you should install an earth?

If both of these questions are answered YES..

I would suggest you need someone with a bit more experience to help you..

Are you still at college? or DIY?

:| ?:|

 

[raustin]

I'm not asking if I should install an earth even though you are right, thats what my previous post was asking. I've replaced the cable from the light switch to the FCU in 1.5mm T&E and then from the FCU to the socket in 2.5mm T&E. All CPC's are now connected.

The FCU (which is plastic) had the front plate and box connected with an earth!

I was trying to ask (not very sucessfully)why someone would not connect the CPC's through and why connect the plastic front plate. Theres no reason for it. Just wnated to check that I hadn't missed something.

 

[SPECIAL LOCATION]

I'm not asking if I should install an earth even though you are right, thats what my previous post was asking. I've replaced the cable from the light switch to the FCU in 1.5mm T&E and then from the FCU to the socket in 2.5mm T&E. All CPC's are now connected.The FCU (which is plastic) had the front plate and box connected with an earth!

I was trying to ask (not very sucessfully)why someone would not connect the CPC's through and why connect the plastic front plate. Theres no reason for it. Just wnated to check that I hadn't missed something.

Sounds to me like you have put right the omissions

and that the original work was done by DIY Bob & Jack the lad of all trades!

And if the previous job was DIY bob's handy work..

TBH absolutely anything could be done...

Reverse polarity.

No CPC's.

Incorrect C.S.A.

No circuit protection at all.

Sellotape joints.

Live cables running along rain gutters.

1.5mm Flex burred in ground with NO additional protection.

Exposed live parts.

etc

etc

etc

As with all the above the Reason's are anyones guess???

 

[ianmacd]

Maybe they didnt want to use the exported earth in something with a concrete floor?