Earth bonding via sub-main??

[johnboy6083]

a sheath test is a test usually carried out on large LV or HV cables to ensure that there is no damage to its sheath. im happy to be corrected though!

i think thjat engineer 54 is highlighting the problems associated with third parties installing gear, that we later have to rely on being done right.

 

[tonys]

The minimum CSA for a bonding conductor where PME conditions apply where the neutral conductor is 35mm² or less is 10mm².
The copper equivilance only applies to the bonding conductor. There is also no reason why conductors cannot provide more than one function.
As such ther is nothing wrong in using the 10mm² core as a bonding conductor bonding between the CU earth bars, and the armour as a CPC for the distribution circuit.
I have no idea what Tonys is going on about, or why he is spouting nonsence.

If your happy using a 10mm conductor as a cpc and main bonding then that's your decision.

The last job I was on, the Main Earth Conductor was 70mm and the Main Bonding Conductors were 50mm connected directly to the Gas and Water services pipes connected back to the MET.

When I installed a 50mm bonding conductor to the boiler room and terminated it into a earth bar and run a 50mm to each metallic flue, it turned into Supplementary bonding and therefore was no longer classed as Main Bonding.

So in comparison the 70mm could be the 16mm and the 50mm could be the 10mm, just some more nonsense for you to digest.

 

[Deleted member 26818]

There is nothing wrong in using the 10mm² conductor as both a CPC and bonding conductor. Although it is not neccessary, as there is the armour of the SWA which can be used as a CPC.
I just don't understand why you refered to the armour's copper equivilance, that is only relevant to bonding conductors where PME conditions apply.

Regulation 541.3 allows an installation's earthing system to be subdivided.

As to why you bonding of the flues suddenly became supplementary, I have no idea.
Regulation 411.3.1.2 requires you to bond incoming services, other installation pipework and ducting along with central heating, air conditioning sytems and exposed metallic structural parts of the building.

There is no Regulation requiring a bonding conductor to be continuous.

 

[tonys]

1, I never said the the 10mm core of the swa was not acceptable to be used as a main bonding conductor.

2, I was working on the lines of the 10mm core and the swa armour amounting to the equivalent of a 16mm copper conductor, the size of a main earth cable.

3. Because who ever told me to install the 50mm and split it at the block got it wrong imo, and justified it by saying to me, it only as to me supplementary bonding, even through I knew full well it should be main equipotential bonding.

4, You show me where you are allowed to link a cable from, say the water bond clamp to the gas bonding clamp without it being continuous.

You might have a copy of this sheet from college courses, this is for information purposes only and not to have a dig either:

The armour of s.w.a cables having cores of less than 95mm 2 core, 700mm 3core or 50mm 4 core are inadequate for PME bonding pruposes.

I'm putting this one to bed now, because it ain't my job, so my input was only an opinion and its up to the poster what he does.

 

[BillyTheSparks]

Thank you to both tonys and spinlondon for your input. I have taken both of your views and suggestions and I will inform the owner that I will need to get floors up, and he'll have to accept this.

I wanted to know if it would have been acceptable to do the bonding via the sub-main (because I'm lazy), and didn't expect a heated discussion.

Thank you both again

 

[Engineer54]

QUOTE by wirepuller... ...''WTF is a sheath test?...edit...that may have been answered by johnboy below...presumably an IR test from the armouring to a ground electrode with the armouring isolated from any earthing??''


Indeed, ....that's Exactly what a sheath test is, except it's a resistance test not an IR test... Any reading between the armouring and ground will indicate sheath damage. ....And you'll be surprised just how many SWA cables fail that test too!!! Whenever you direct bury a SWA cable, a sheath test should always be performed prior to any permanent glanding off of the cable!!!

So wirepuller, do you think that this additional CU, comes under your previous criteria as being acceptable???


QUOTE by johnboy6083 ...''I think thjat engineer 54 is highlighting the problems associated with third parties installing gear, that we later have to rely on being done right''.

Correct, and what's the betting that this cable hasn't been laid/installed in the ground correctly!!! Probably been back filled with the same material that was excavated, ...Sharp stones and all!!! Wouldn't mind betting that there's sharp bends round the corners of the house too, because the trench (if it is a trench in the true sense of the word) wasn't made wide enough.

 

[Deleted member 9648]

Thanks for clarifying the sheath test......
Regarding the sparate DB being acceptable...well I cant see any reason why it is unacceptable,it is just an alternative installation method.As long as correct labelling and identification is provided I cant see any reason to call it unacceptable or any reason to suggest it is a cowboy practice.Show me a regulation which states only one DB can serve a single property.....It is up to the installer to decide whether to run final circuits right back ,or a distribution circuit to a local DB.
The part unclear here though is whether the distribution circuit runs outside underground..(and hence your sheath test)...or on the outside wall of the house....If a separate DB is to be installed I would not want the SWA running underground and back into the house,however I originally read the OP and presumed the swa is clipped surface,in which case your sheath test would be redundant.
Dont think we are going to agree on the separate DB issue so lets just agree to disagree.

 

[Engineer54]

Wirepuller,

On the new SWA cable run, ....if you look at the photo link of the floor plan, it's clearly noted as being underground!!!

As far as the additional CU, ....Agree!!!

Now i'll tell you a little secret, ...haha!! ...I have 3 CU's in my house here!!!! Not of my choosing i might add, ....and went ballistic when i found out what the local sparks had done, even after giving him a detailed layout of how i wanted everything to be!! I now have a 3ph CU downstairs in my garage (where i wanted the CU located) and a 3ph CU upstairs on the landing!!!!

The last CU (single ph) is in the external services/boiler/s/pool room, that supplies those services, and the external lighting and power i subsequently installed. No problem with that CU as it is only dealing with services, that are located externally ....I suppose at least he got my in-wall speaker layouts correct. ..lol!!

 

[Deleted member 9648]

Missed the floor plan Engineer54....the result of skimming through threads sometimes!

 

[Engineer54]

Just one more thought about that SWA cable for the Kitchen circuits, ....Wouldn't that be ''Notifiable'' under your new rules in the UK?? And was it??

 

[Deleted member 9648]

Any alterations in a Kitchen are notifiable,even alterations to existing circuits..along with new circuits anywhere in a domestic....dont know whether the OP has notified.

 

[johnboy6083]

engineer54, do you need any specialist equipment to carry out a sheath test on LV cables, or can you use an IR tester/low ohms tester? i cant see any reason why it wouldnt work with an IR tester, providing the ground wasnt bone dry, which it isnt usually in the UK?

Also on a power station i worked on a last year, the singlecore LV supplies from the tranny to the ACB were covered in graphite. was that to enhance the results of a sheath test?

Thanks,

John

 

[tonys]

You can use a IR test to establish if an item is an extraneous conductive part, so in theory whats to stop us using the same test on the armour to see if it as come in contact with Earth ?

 

[johnboy6083]

i was thinking along the same lines. i wonder how effective the test would be though. i think that a higher voltage would be needed though to ensure that any gap in the sheath would be shown in the results.

 

[Engineer54]

Tony/Johnboy,

I didn't say that you couldn't do an IR test, just that it is normally conducted using the ''low ohm'' test method. Pumping 500/1000 volts into this test can sometimes give a false reading, by the voltage finding maybe partially damaged sheath (scuffed but not broken/penetrated) weak spot(s). I've never had these sort of tests conducted, using IR measurements, as i want to see if it fails without any injected voltages, ....as is if you like ...lol!!!


Johnboy

No, no specialist test equipment is required to undertake a sheath test, just your standard low ohm range meter....

...I've personally never seen graphite used on any cables sheathing, and have no idea why either!!! Maybe someone here may be able to give you a reason??