To bond or not bond

[Rutts35]

We are installing some metal partitioning in work. It's powder coated frames with glass inserts around 7ft high. It's mounted on an existing parquet flooring and bolted through to the concrete slab underneath. Now, I'm pretty sure, when I test it that it will be isolated from the MET so it won't require bonding. However, as there will 6 entry doors along its perimeter, we are required to run some power to each point. The only feasible way is mounting trunking along the top of the partitioning (there is a 100mm rail atop of the partitioning that will take some trunking). My initial thought and discussion with the person installing in was to run it PVC trunking and attach it using nylon bolts. It's only taking 2.5mm singles and not a huge amount of them. Plus, with the PVC we can create compartments should data be required as well. Using white plastic conduit drops from the trunking to the points required. The thinking being all of the electrical items are isolated from any of the framework. Plus, lower weight than galv and lees work than galv conduit drops from the trunking to the points. We can still use white plastic conduit but not sure how this would look. Not sure if this sounds nuts or overkill.

However, the installer decided to run in galv trunking. My thinking with this is that running singles in this means that the trunking could become live under fault conditions and will need bonding, etc.... With bonded trunking sat atop the metal panels fixed with metal screws (couldn't really use plastic for galv trunking) we are now bringing an earthy potential to the partitioning. I'll have to test but I'm not sure if the continuity of the panels is continuous. so, would this mean bonding the partitioning? It's not a short run either. the trunking comes in at 60mtrs for the entire perimeter!

Hope this makes sense. Am I waffling bollox, am I worrying over nothing or should we be doing something different?

Thanks

Rutts

 

[Andy™]

the trunking will be an exposed conductive part and will need an earth. the framework its self cannot become live, other than through a fault with something else, which ADS should deal with. and it cant introduce a potential from outside so isnt extraneous

dont forget, the major flaw in your plastic & nylon bolts, how do you plan on the wiring being adequately supported if there's a fire?

 

[Rutts35]

Granted it isn't extraneous but the trunking will be screwed to the top of the framework. So will this pose a problem as the frame work is now an extension of the trunking in terms of continuity or is this no an issue as we will have bonded the trunking?

I've just had another look at what's been installed today and two ends of the partitioning are bolt to the steel frame work of an internal office (picture all of this inside a large hall). So when I test back to the MET it may be that the partitioning isn't actually isolated as I thought it would be.

Without boring you about the lay out the fire risk is really and issue. I've had this discussion with my Niccy asses last year. With the layout and size of the hall for anything to melt and fall off the fire would have to be directly underneath the installation which would mean you wouldn't be running through it anyway. Heat build up from any fire wouldn't be a concern either.

 

[Andy™]

the partition isnt 'an extension of the trunking' its merely a wall which happens to have something electrical installed on it

if the trunking is installed correctly and earthed, then where exactly is any voltage that could make the wall live going to  come from, and what benefit would bonding it be?

for the cable supports, the issue isnt people running through it as such, its the fire men / women who have to go in to resuse people / put the fire out. although if its really bad than i doubt they would be going in just to put the fire out, unless they knew someone was still inside

 

[Rutts35]

In BS7671 the fire risk is both evacuation and fire fighting but it isn't an issue in our building to be honest. Plus we already have 100mtrs of galv trunking to use up!!

As for the metallic trunking. Fair point. The only issue I have at the moment, as mentioned above, is that the partition is now connected to other steel structures so may be introducing a potential. So could it be extraneous because of this and would I use the Rcp formula that's GN8?

BTW, thanks for your input on this mate.  :Salute

 

[Evans Electric]

My thinking with this is that running singles in this means that the trunking could become live under fault conditions and will need bonding, etc.

Singles in steel trunking is the normal way ,  the whole thing sounds fine to me , obviously the trunking will need to be earthed  but thats about it for me ...stop digging .  

 

[Andy™]

So could it be extraneous because of this

read the definition of extraneous in part 2

if it is connected to an extraneous part then that part should be bonded as necessary, but then we are back to if that is bonded, then where is the voltage on thepartition going to come from and what use would bonding it be?

 

[Rutts35]

Singles in steel trunking is the normal way ,  the whole thing sounds fine to me , obviously the trunking will need to be earthed  but thats about it for me ...stop digging .  

Yep, you're right. I'm over thinking the whole thing. Thanks for the sanity check.  :signthankspin:

 

[Rutts35]

Thanks to Andy as well.  :signthankspin: