Main Bonding and Cross Bonding question?

[chrisgc]

HiI need to know a few answers regarding cross bonding and main bonding, am hoping some of you can advise please:I have attached pictures with the questions on the pictures to save double typing:



Would appreciate some input please.

Thanks
Chris

 

[telectrix]

1. that's well good.
2. bond gas as near as possible to where it enters the property on the inside.
3. wander lead from MET to boiler pipes. measure the resistance.
4. as 3.

 

[chrisgc]

Hi thanks for the reply,

Just a few questions with:

Number 1 - the main earth cable to earth rod - I would have thought it would be thicker due to it needing to be 16mm or 25mm? I know you know best but just asking so I can gain more of an understanding.

Number 2 - The main gas pipe enters the property but is not visable as it goes under the doorway and is under concrete flooring - so where is the best place to main bond from as it appears only visible from the outside?

Number 3 and 4 - why is measuring the resistance on the pipes under the boiler needed? Would it need cross bonding regardless?

I am not questioning your knowledge by the way so please dont take offence - just want to understand and learn.

 

[telectrix]

Number 1 - the main earth cable to earth rod - I would have thought it would be thicker due to it needing to be 16mm or 25mm? I know you know best but just asking so I can gain more of an understanding 6mm min for TT earthing ( 2.5mm if mechanically protected)

Number 2 - The main gas pipe enters the property but is not visable as it goes under the doorway and is under concrete flooring - so where is the best place to main bond from as it appears only visible from the outside? either bond outside, or wherever it becomes exposed inside the house.

Number 3 and 4 - why is measuring the resistance on the pipes under the boiler needed? Would it need cross bonding regardless? if you measure the resistance from the MET to the pipes and get a reading of 0.05 ohms or less, then you can consider them to be reliably connected to earth.

I am not questioning your knowledge by the way so please dont take offence - just want to understand and learn.

 

[chrisgc]

Telectrix,

Thank you so much for the info.

Just a couple more to clarify Number 2:

Do you always try and put your bond clamp inside the property (if possible) as opposed to outside? (obviously in my case it has to be outside).

Is this earth clamp ok to use for outside use:
http://www.******************/Images/Products/size_3/EC14.JPG
Or should it be a specific type due to the elements?

And should the hole in the wall for the main bond be a seperate hole in the wall from the earth cable that enters from the earth rod?

Edit: With regards to the 0.5ohm or less reading indicating its reliably connected to earth - where can I found that in the BGB or OSG?

 

[Engineer54]

Did you install that earth rod??

 

[chrisgc]

No was not installed by me.

A company in Swindon moved the consumer unit and earth rod around to different side of property - this must have been at least 6 months ago. Why did you ask?

Incidentally they have still yet to send a certificate of the works done!

 

[Engineer54]

Why?? It's a 1.2 M 3/8'' rod with around 20cm stuck out of the ground, with a numbty Earth box sat on top of it!! And installed in just about the worst position you could wish for!!! Where all the original building rubble will be, not that would have been a problem, the dammed rod doesn't go down deep enough to hit any rubble!!! That rod will be about as stable as an alcoholic on a Friday night binge!! lol!!!

 

[brman]

I am getting confused. I thought there was no specific need to bond boiler pipework, just the need to comply with the R<=50/Ia for extraneous parts?
So you can go much higher than 0.05 ohms depending on the protective device/RCDs.

Or am I getting my bonding regs muddled up?

 

[chrisgc]

Why?? It's a 1.2 M 3/8'' rod with around 20cm stuck out of the ground, with a numbty Earth box sat on top of it!! And installed in just about the worst position you could wish for!!! Where all the original building rubble will be, not that would have been a problem, the dammed rod doesn't go down deep enough to hit any rubble!!! That rod will be about as stable as an alcoholic on a Friday night binge!! lol!!!

I was under the impression it should be buried in a pit?

And your right - it does not seem stable at all. Personally I think they knew the job was a shoddy one and have not given a certificate.

I did say to my brother that he should get the certificate asap as it will have test results on etc but as he still has no cert I am wondering if they have even tested the system?

But back to my point of the original questions any chance the following could be replied to:

Telectrix,

Thank you so much for the info.

Just a couple more to clarify Number 2:

Do you always try and put your bond clamp inside the property (if possible) as opposed to outside? (obviously in my case it has to be outside).

Is this earth clamp ok to use for outside use:
http://www.******************/Images...ize_3/EC14.JPG
Or should it be a specific type due to the elements?

And should the hole in the wall for the main bond be a seperate hole in the wall from the earth cable that enters from the earth rod?

Edit: With regards to the 0.5ohm or less reading indicating its reliably connected to earth - where can I found that in the BGB or OSG?

 

[telectrix]

Do you always try and put your bond clamp inside the property (if possible) as opposed to outside? (obviously in my case it has to be outside). where's the gas meter? that gas pipe must surface inside somewhere.

Is this earth clamp ok to use for outside use:
http://www.******************/Images...ize_3/EC14.JPG
Or should it be a specific type due to the elements?

And should the hole in the wall for the main bond be a seperate hole in the wall from the earth cable that enters from the earth rod? no

Edit: With regards to the 0.5ohm or less reading indicating its reliably connected to earth - where can I found that in the BGB or OSG? can't remember where.

 

[Richard Burns]

Do you always try and put your bond clamp inside the property (if possible) as opposed to outside? (obviously in my case it has to be outside). Bonding ideally should be inside the property after the meter (within 600mm) and before any branch pipework. Though it can be bonded outside if required.

Is this earth clamp ok to use for outside use:
http://www.******************/Images/Products/size_3/EC14.JPG
Or should it be a specific type due to the elements?
This clamp is only suitable for internal use, you need the EC15 or EC16 clamp for use outside.

And should the hole in the wall for the main bond be a seperate hole in the wall from the earth cable that enters from the earth rod? No

Edit: With regards to the 0.5ohm or less reading indicating its reliably connected to earth - where can I found that in the BGB or OSG?
This is not ,I think, in BGB or OSG, it is in GN3, the value is 0.05 ohm not 0.5ohm. This is a general rule of thumb to see if there is supplementary bonding in place and it can be considered to be in place if the continuity value is less than 0.05 ohm.

hope this helps

 

[telectrix]

This is not ,I think, in BGB or OSG, it is in GN3, the value is 0.05 ohm not 0.5ohm. This is a general rule of thumb to see if there is supplementary bonding in place and it can be considered to be in place if the continuity value is less than 0.05 ohm.

that's why i couldn't think where.

 

[chrisgc]

Right,

Now let me try and find the actual gas meter (its my brothers place).

Am sure I couldnt see one or remember the location of it though?

 

[brman]

GN3 does indeed quote the 0.05 ohm for where bonding is required. However the BGB reg 415.2.2 gives the method for determining the effectiveness of suplimentary bonding between exposed conductive parts and extraneous conductive parts. This uses the R<=50/Ia formula so gives a much bigger resistance than 0.05.

Further, for bathrooms, reg 701.415.2 suggests using 415.2.2 to determine the effectivenesss of the connection between extraneous conductive parts and the MET.

I've got to say the regs are not exactly clear here which is probably why so many get confused (me included! )

EDIT: Btw, why are you cross bonding? Do I take it the system isn't to the 17th Ed regs?