Exothermic welds VS Clamps Connections 5

[joji90]

Hello Everyone,
Site: Netherlands, Facility: Pharmaceutical
We have a grounding ring grid underground a building and the connections from this to the Earthing bars inside the building are supposed to be exothermic welds (According to a drawing which was produced earlier). the client is now asking if we can use clamps instead of the welds. I went through the standards applicable in Netherlands and in general and there was no mention of this requirement strictly mentioned. Are exothermic welds(Cadwelds) mandatory?
Please see the yellow highlighted connections below, that’s the connection

Thanks in advance,

 

[jghrist]

I don't know if they are required by Netherlands code, but if the plans and contract require exothermal welds, then they are mandatory unless the Owner allows an exception. I would not accept a clamp connection below grade. Compression connectors designed for below grade ground connections could be considered.

 

[waross]

I haven't seen a recent Canadian code, but my last edition of the code allows ring type compression connectors on ground conductors but not "C" type compression connectors.
In regards to exothermic welds,they may not be in good in practice as they are on paper.
If everything is new and clean then exothermic welds are good.
If cables have been exposed to the atmosphere and have surface corrosion, exothermic welds may not be as good.
Old school, when the thermite charges were loaded and fire manually, a skilled operator would recognize poor conditions and over-charge the mould so as to generate the extra heat needed for a good weld under poor conditions.
With the new pre-sealed and remotely fired thermite charges, operator judgment is no longer possible.
Poor conditions equals poor connections.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[dik]

Thanks for the 'heads up' on exothermic... I always thought they were the best.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[waross]

I would consider a good thermite weld to be the best.
Cleaning large cables prior to welding may not be effective if the individual strands have some surface corrosion.
One old school trip that still works is to heat the cables up with a torch before welding.
Some heat is needed to ensure that the cables are dry.
One drop of water and you may see molten metal raining down. (If the mould doesn't explode instead of the charge going straight up.)
But a weld on bad material may have better results if a large torch is used to heat the cables up very hot.
That is to the point that the copper starts to change colour.
Wear thick, heavy gloves.
If the cables have been exposed to the atmosphere or have been in outside storage for a long time, welds may be less than perfect.
When welding old cables, we would gap the cables in the mould and add extra thermite to fill in the space and add extra heat.
We were able to make good welds on 1000 mcm cables that were turning green with surface corrosion by gapping and heating.
You can't easily add to the charge with the new methods.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

joji90 (Petroleum)(OP)6 Nov 23 12:28
" #1. Site: Netherlands, Facility: Pharmaceutical. We have a grounding ring grid underground a building and the connections from this to the Earthing bars inside the building are supposed to be exothermic welds (According to a drawing which was produced earlier). the client is now asking if we can use clamps instead of the welds".
I am NOT familiar with the practice/code in Netherlands. It is my personal opinion that especially connection placed under ground, exothermic weld is preferred for long lasting joints; that are NOT inspected/tested regularly. On the other hand, the lightning down conductor is usually terminated on the wall say 1.5m above ground with compression plates, this is to allow for future inspection/test.
" #2.... in general and there was no mention of this requirement strictly mentioned. Are exothermic welds(Cadwelds) mandatory?"
For joints placed under ground where future inspection/test is not practical, a clamping joint can not ensure a long lasting joint. Exothermic is one of the methods, unless other method proved to be as durable/reliable, Exothermic weld can be easily carried out at site, simple tooling and economical.
Caution: exothermic welding process is prohibited in locations having explosive gas !
Che Kuan Yau (Singapore)

 

[7anoter4]

There are national codes recommending periodical testing of grounding conductors.
If the connections are welded you have to do some where disconnecting points.
However, according to the manufacturer instruction book, the temperature of different
connection way limits the permissible grounding current and then the grounding conductor cross section. For pressure type connection the temperature is limited to 450 oC and for exothermic welded connection 1083.
See:
ERITECH Grounding Products and Systems

https://5.imimg.com/data5/DI/GK/MY-21164678/erico-earthing-system.pdf

 

[dik]

Is it possible to put an ohmmeter across the connection to confirm? or is it just too much 'trouble'?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[waross]

It is a problem of resolution, dik.
More accurate is a device known as a "Ductor".
The ductor puts a fairly high current across the joint and measures the resulting voltage drop.
With the very low resistance of a good ground connection, the resistance of the ohmmeter leads and possible contact resistance may be greater than the resistance of the joint under test.
An analogy to measuring contact resistance with a multi meter may be measuring 2"x4"s to build a house with the odometer on your car.

Is it possible to put an ohmmeter across the connection to confirm? Not accurately.
Is it possible to put a ductor across the connection to confirm? Yes

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[7anoter4]

In order to find damaged parts of a grounding grid, there are some testing ways, like the following one-for instance:

https://www.nvent.com/sites/default/files/acquiadam/assets/VPGGIT.pdf

 

[3I0]

Can't speak to the Netherlands but in Canada I have seen a lot of IEEE 837 qualified compression style connections (Burndy Hyground) used underground in industrial/mining facilities - where for example they might be designed with a 25 year life expectancy and there is some cost/time savings to be had during installation. In the utility world I only spec exothermic connections though for buried or embedded grounding connections.

The integrity testing I have seen done here has either used a ductor for short distances, or for larger sites utilizes a 12V gel cell battery at a 'reference' ground location, then long roll(s) of multiconductor light gauge wire are used to bring a Kelvin connection to remote points and a handheld meter is used to calculate the interconnected resistance at specific points.

 

[dik]

Thanks gentlemen... I'd assumed the difference between a good connection and one that was not so good was remarkable. The current approach is more positive, and not as reliant on the contact of the 'leads'. Thanks.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik