Testing extraneous conductive part

[Ian1981]

But what is the use of testing between 2 points if they are connected together somewhere in the installation?
Like for instance a gas pipe and a known earth, but the gas pipe is connected at one end to the boiler which is connected to earth by a cpc. The cpc needs disconnecting at the boiler end then test between earth and the pipe.
That’s just one example you do not necessarily have that scenario every time of having to disconnecting anything.

 

[Midwest]

Thats the idea of this test; to discover if somehow two points are connected in someway or not.

 

[telectrix]

you could always poke it with a "live" wire. if it goes bang, it's extraneous. .....trainees.DON'T TRY THIS AT HOME>

 

[Ian1981]

Thats the idea of this test; to discover if somehow two points are connected in someway or not.

Extract taken from NAPITS site guide, the point is actually to find out if the metallic conductive part is introducing an earth potential into the installation and by testing between the earth of the installation and the conductive part, that the conductive part under test has a high enough resistance to earth that it doesn’t require bonding to the earthing arrangement of the installation

It’s

 

[static zap]

Inverse logic -Bang once then no more ? Now cured.

if it goes bang, it's extraneous.

---NOT good advice -- but get's you thinking !
22k more of a fizzle ..
(Door bell /out door LV lighting /CCTVprobably broke now)

 

[Midwest]

Extract taken from NAPITS site guide, the point is actually to find out if the metallic conductive part is introducing an earth potential into the installation and by testing between the earth of the installation and the conductive part, that the conductive part under test has a high enough resistance to earth that it doesn’t require bonding to the earthing arrangement of the installation

Fair enough. But that’s just one piece of guidance that says dis the cpc’s, against the two I posted, which suggested using cpc’s as the known earth.

Does Guidance Note 3 or 8 make any suggestions?

 

[Ian1981]

Fair enough. But that’s just one piece of guidance that says dis the cpc’s, against the two I posted, which suggested using cpc’s as the known earth.

Does Guidance Note 3 or 8 make any suggestions?

It’s only relevant to disconnect the cpc’s if required, you don’t always need to if the metallic part has not been connected together with a cpc to earth .
I don’t think gn3 covers this subject but gn5 and 8 do so I’ll have a dig out

 

[Lister1987]

you could always poke it with a "live" wire. if it goes bang, it's extraneous. .....trainees.DON'T TRY THIS AT HOME>

But I'm ok to do it in colleege....right? ?

 

[Zdb]

Thanks for all of the replies.

Interesting topic. Might have to invest in a copy of GN8.

 

[Midwest]

Thanks for all of the replies.

Interesting topic. Might have to invest in a copy of GN8.

You can tell us the answer then

 

[Zdb]

It says in GN8 to test between the MET and the suspected extraneous conductive part.

Not a problem in a domestic installation but a known/proven connection to earth is more practical in a commercial/industrial scenario.

 

[Zdb]

So, I carried out this test yesterday on some cable basket I put up for some Cat6 data cables. I tested between a known earth from a socket outlet and the cable basket and I got a reading of 0.47 ohms. Nice low reading via parallel paths (earthed structural metal work). I then bonded the basket using some 6mm.

So am I right in thinking that this needed bonding due to the reading, and if the reading had been above 23,000 ohms then it wouldn't have needed bonding?

 

[Midwest]

I don't think it needed bonding. Here's a view from someone else;

Does a Metallic Cable Tray Require Earthing or Bonding? | Tradeskills4u

A. In short the answer is ‘depends’ but the answer could be ‘earthing’, ‘bonding’ or ‘neither’ depending on the circumstances. Looking at each of these in turn: If the tray is an exposed conductive part it requires earthing. If the tray is and extraneous conductive part it requires bonding. If...

www.tradeskills4u.co.uk

 

[Mike Johnson]

It's usual in France to have one of these between the earth rod and the DB on the outside wall of any domestic property: Barrette de coupure de terre haute P.65 mm LEGRAND | Leroy Merlin - https://www.leroymerlin.fr/v3/p/produits/barrette-de-coupure-de-terre-haute-p-65-mm-legrand-e1401450423 makes checking extraneous conductive parts relatively easy loosen the top nut and swing the brass joiner out of the way.

 

[static zap]

"Barrette de coupure de terre haute"

makes checking extraneous conductive parts relatively easy loosen the top nut and swing the brass joiner out of the way.

May be clamp it first ?

 

[Mike Johnson]

Clamp what where?

 

[static zap]

Clamp what where?

Make sure no current is entering / leaving that exotic french "link"
before opening it and having it turn into something that may unexpectedly exceed "touch voltage limits" !
(resp to your sig---- all my fingers too !)

 

[Mike Johnson]

If any current was entering that exotic French link then the Disconjoncteur tetrapolair de branchement would trip, can't see how any current could enter the TT earthing system without tripping something, perhaps even the Parafonudre Disconjoncteur Quata would go first.

 

[static zap]

Are you sure ?
Is

the Disconjoncteur tetrapolair de branchement would trip,

All equipment 100% reliable , trustworthy !
Could be staking your / someone else's life on the assumption?

 

[Mike Johnson]

There are safety procedures that we all go through before we carry out any work on a system, why are you persevering with this premise?