Bathroom bonding with steel stud walls

[Richard Redman]

Hi all, after some advise on bonding in a bathroom, ive fitted an electric shower, its RCD protected and ive bonded the water pipes. 2 of the walls in the bathroom are steel stud walls, another electrician says it doesnt need bonding as its on a RCD ? Help

 

[Deleted member 26818]

The main problem here was not that the Painter and Decorator who conducted the I&T was not qualified, was not the fact that QS passed the certification, was not the fact that the NICEIC registered company allowed the situation to save money.
It was simply the fact that the dry liners were not aware of or ignored the prescribed cable routes.

 

[westward10]

Totally agree, what is the argument against earthing the metal stud frame during first fix?

Are these not supposed to be accessible for inspection purposes?

 

[Leesparkykent]

bonding or earthing metal stud walls is this the 15th edition?

 

[Andy-1960]

Going back to the article where the girl died, how could this have been prevented?

 

[Deleted member 26818]

Going back to the article where the girl died, how could this have been prevented?

Mechanical protection, earthed sheath or RCD protection.
Perhaps even by educating the dry liners as to where prescribed routes are?
The Coroner in the case did suggest that drawings showing cable routes be provided by the electrical contractors for other trades.
He also indicated he was not happy with the NICEIC QS system, stating something along the lines of: it is flawed and open for misuse.

 

[Midwest]

I can't understand the point of bonding the metal stud wall construction. Some of the installations I've seen, you would have to run several cables to effectively bond the studwork. The requirement for RCD protection for cables installed in such an installation (with no earthed mechanical protection), came in for the 17th Ed, perhaps because of this incident?

So OP, bonding your metal stud work, seems ineffective and unnecessary. Why have you bonded the metal pipes?
You may have made something that was not extraneous now more dangerous than it was before.

 

[Richard Redman]

I can't understand the point of bonding the metal stud wall construction. Some of the installations I've seen, you would have to run several cables to effectively bond the studwork. The requirement for RCD protection for cables installed in such an installation (with no earthed mechanical protection), came in for the 17th Ed, perhaps because of this incident?

So OP, bonding your metal stud work, seems ineffective and unnecessary. Why have you bonded the metal pipes?
You may have made something that was not extraneous now more dangerous than it was before.

How can it be more dangerous than it was before ?

 

[Deleted member 26818]

Well, by bonding the steel studs, you will now have fault current inside the wall if there is an earth fault in the installation.
As long as the steel studs are mechanically connected, there shouldn't be a problem with sparks jumping from one to the other.

 

[Richard Redman]

Well, by bonding the steel studs, you will now have fault current inside the wall if there is an earth fault in the installation.
As long as the steel studs are mechanically connected, there shouldn't be a problem with sparks jumping from one to the other.

Right ok.

Well, by bonding the steel studs, you will now have fault current inside the wall if there is an earth fault in the installation.
As long as the steel studs are mechanically connected, there shouldn't be a problem with sparks jumping from one to the other.

Ok, so this is what i have done.
New electric shower has been fitted, and a new circuit from 40A breaker RCD protected.
The pipework to the bath is bonded, but some plastic fittings have been used here and there, so have run a 10mm earth cable from MET to the pipe work under the bath so i kbow the pipes are bonded.
Two walls are steel stud walls, so have bonded from pipework to the steel stud.
Does this sound right ??

 

[Midwest]

How can it be more dangerous than it was before ?

Because now, you have 'earthed' something that previously (potentially) was not connected to the MET, therefore is now a path to earth (there are others, who will described this in more scientific manner). If you feel the need to earth the metal pipe work (that may have not been extraneous), what about any metal single fuel towel radiator fed by plastic pipes, metal bath, aluminium windows?

Did you watch the video Pete posted, #3?

Edit; if you tested the metal pipework, and it was extraneous, then you have made the installation safer than it was.

 

[Wilko]

On the accident info ... I don't quite get why the tragedy occurred? The cable in the metal stud wall was penetrated by a screw (Sod's law) and the screw contacted the live only (Sod's law again) it made the frame live. Got it. But when the water first saturated the area and touched the steel frame the RCD should have tripped ? Or failing that when the person touched a bonded tap while standing in the live (but electrically isolated) puddle and provided a path then the RCD would have tripped? What have I missed ?

 

[Andy-1960]

On the accident info ... I don't quite get why the tragedy occurred? The cable in the metal stud wall was penetrated by a screw (Sod's law) and the screw contacted the live only (Sod's law again) it made the frame live. Got it. But when the water first saturated the area and touched the steel frame the RCD should have tripped ? Or failing that when the person touched a bonded tap while standing in the live (but electrically isolated) puddle and provided a path then the RCD would have tripped? What have I missed ?

Was there an RCD? Maybe the floor was insulated?

 

[Deleted member 26818]

No RCD, flat was wired to the 16th edition.

 

[Wilko]

No RCD, flat was wired to the 16th edition.

Thanks - makes sense.
Thinking about how this problem could have been picked up during an inspection - they imply as the chap was not qualified, he didn't inspect competently. But it seems possible (to me anyway) the circuit could have a compliant IR until the area was inundated, and so the circuit would have appeared normal ?

 

[Ian1981]

Having the protective conductors connected to Earth during an insulation resistance test the test has the advantage that it might detect any contact between a live conductor and any ‘unearthed’ metalwork (such as a concealed part of the building fabric or an isolated section of pipework). If the unearthed metalwork has some relatively low resistance contact with Earth (even hundreds of thousands of ohms), the defect can be identified by the person using the insulation test instrument. Such a dangerous defect might be caused by the penetration of a nail, screw or similar making contact with a live conductor and the unearthed metalwork. If not corrected, the defect would create a risk of electric shock.
Key word being MIGHT.