Garage Metalwork

[Spearmint]

I'm in the middle of putting some lighting and socket outlets in my garage, nothing fancy just a few of each as you'd expect. I've run it in SWA ,which will be buried eventually, from the existing CU in the house on it's own circuit. Earthing arrangement is TT which reads 14.67 ohms, not bad I thought been in for 20+ years.

There's a cold water feed coming from the house underground and pops back up in the garage, now this is bonded as you'd expect in the house back to the MET which reads 0.54 ohms when testing against the new garage CU earth bar. So this got me thinking... it isn't extraneous as testing shows it's already connected, nor is this a separate dwelling so in effect is within the same installation.

My gut feeling is to supplementary bond it regardless due to risk of introducing a difference in potential should there be an issue with the main bond in the house, but as far as the regs are concerned???

Thoughts?

 

[Leesparkykent]

I'm in the middle of putting some lighting and socket outlets in my garage, nothing fancy just a few of each as you'd expect. I've run it in SWA ,which will be buried eventually, from the existing CU in the house on it's own circuit. Earthing arrangement is TT which reads 14.67 ohms, not bad I thought been in for 20+ years.

There's a cold water feed coming from the house underground and pops back up in the garage, now this is bonded as you'd expect in the house back to the MET which reads 0.54 ohms when testing against the new garage CU earth bar. So this got me thinking... it isn't extraneous as testing shows it's already connected, nor is this a separate dwelling so in effect is within the same installation.

My gut feeling is to supplementary bond it regardless due to risk of introducing a difference in potential should there be an issue with the main bond in the house, but as far as the regs are concerned???

Thoughts?

Is the house DB TT or have you just done this at the garage DB?

 

[Spearmint]

Is the house DB TT or have you just done this at the garage DB?

Sorry wasn't clear. The house is TT, the garage CU is to be connected to it via 3rd core in the SWA.

 

[Leesparkykent]

What size SWA?

 

[davesparks]

The test for an extraneous part must be carried out with the earthing conductor disconnected from the MET of disconnect link open.

The test you have carried out with all main bonds connected is what you would do to establish whether supplementary bonding is required or not

 

[Spearmint]

What size SWA?

2.5mm^2

 

[Leesparkykent]

2.5mm^2

Do what dave said to establish if it's extraneous or not then if it requires bonding the CSA of the SWA you have installed is to small. So you will have to replace the SWA or run in a separate bond.

 

[Spearmint]

The test for an extraneous part must be carried out with the earthing conductor disconnected from the MET of disconnect link open.

The test you have carried out with all main bonds connected is what you would do to establish whether supplementary bonding is required or not

Disconnected? Surely all metallic pipework would appear extraneous if you tested against the main earthing conductor disconnected? I have quickly tested against the garage CU (only because I was in there) which returned 0M ohms... will be going back with a wander lead to test this weekend hopefully!

Do what dave said to establish if it's extraneous or not then if it requires bonding the CSA of the SWA you have installed is to small. So you will have to replace the SWA or run in a separate bond.

Thought of that already, was going to get a length of G/Y when I stopped and questioned myself whether or not this actually required bonding.

 

[Pete999]

https://www.youtube.com/watch?v=v38PfIVy2rI

 

[Engineer54]

There's a cold water feed coming from the house underground and pops back up in the garage, now this is bonded as you'd expect in the house back to the MET

Why would you need to test this water pipe?/ If it's metal and has been directly buried underground to the garage it's gonna be extraneous without a shadow of a doubt. It doesn't matter a jot whether the incoming metal water pipe has been main bonded at the house, it will still need bonding at the garage to the garages EMT...

 

[spark 68]

Why would you need to test this water pipe?/ If it's metal and has been directly buried underground to the garage it's gonna be extraneous without a shadow of a doubt. It doesn't matter a jot whether the incoming metal water pipe has been main bonded at the house, it will still need bonding at the garage to the garages EMT...

Would it though ?, if the garage is integral to the house (part of the same building).

I would probably add the extra bond if it was easy enough to do, but would it actually require it ? I would personally say not in this case.

 

[Engineer54]

Would it though ?, if the garage is integral to the house (part of the same building).

I would probably add the extra bond if it was easy enough to do, but would it actually require it ? I would personally say not in this case.

If it's an integral garage it would be one and the same equipotential zone, and the power and lighting circuits would i imagine be supplied from the house CU.

 

[spark 68]

If it's an integral garage it would be one and the same equipotential zone, and the power and lighting circuits would i imagine be supplied from the house CU.

That is how I would treat it, the OP said it is integral, this is really no different to having a separate additional CU in any other room in the house.

I would agree if the building was separate

 

[Engineer54]

That is how I would treat it, the OP said it is integral, this is really no different to having a separate additional CU in any other room in the house.

I would agree if the building was separate

Did he, where as i must have missed that bit of info??

 

[spark 68]

I'm in the middle of putting some lighting and socket outlets in my garage, nothing fancy just a few of each as you'd expect. I've run it in SWA ,which will be buried eventually, from the existing CU in the house on it's own circuit. Earthing arrangement is TT which reads 14.67 ohms, not bad I thought been in for 20+ years.

There's a cold water feed coming from the house underground and pops back up in the garage, now this is bonded as you'd expect in the house back to the MET which reads 0.54 ohms when testing against the new garage CU earth bar. So this got me thinking... it isn't extraneous as testing shows it's already connected, nor is this a separate dwelling so in effect is within the same installation.

My gut feeling is to supplementary bond it regardless due to risk of introducing a difference in potential should there be an issue with the main bond in the house, but as far as the regs are concerned???

Thoughts?

Here in bold, now as to whether it is the type of garage with a doorway into the house is another matter

 

[Engineer54]

Think he's talking about something different, ...why would he need to bury a sub main cable to the garage if it was an integral garage??

 

[spark 68]

Well this is it, how are we supposed to advise without seeing the job, or at least a clear description ?

It doesn't help that the building regs classification does not quite marry up with BS7671, it could be classed as integral or separate depending on which way you look at it, my gut feeling would have been to make my sub-main 6mm 3 core, as it is TT, or possibly even 10mm in case they ever update it to PME, especially if it is buried.

 

[Engineer54]

Well this is it, how are we supposed to advise without seeing the job, or at least a clear description ?

It doesn't help that the building regs classification does not quite marry up with BS7671, it could be classed as integral or separate depending on which way you look at it, my gut feeling would have been to make my sub-main 6mm 3 core, as it is TT, or possibly even 10mm in case they ever update it to PME, especially if it is buried.

Let's see if he comes back to clear this point up... lol!!

 

[davesparks]

in a domestic installation with an outbuilding and TT supply I would be looking to install a submain with a cpc suitably sized to allow me to put a rod(s) in at the outbuilding which is connected back to the MET to add to the existing earth electrode(s).

If the existing Ra really is ~14ohms i'm sure it could be improved down to a very nice value with a bit more effort.

 

[Spearmint]

Think he's talking about something different, ...why would he need to bury a sub main cable to the garage if it was an integral garage??

You're correct. The garage is a separate building to the house, it's about three metres away from the main building. My use of the word dwelling was more relating to it being unoccupied, not a living space.