To Bond or not too Bond??

[Sharpend]

So working on a new build shop with flats above. 

The outline structure of shop is steel, the internal walls are heavy duty metal sectional frame (metsec). The whole building is having a lightning protection system installed to roof with tape run down sides to ground -fairly standard. 

From within the shop we usually install a 50mm earth bond to structure. 

So far pretty standard,

however when considering the flats above my concerns are this:

the flats are contstructed from the metsec with the outer most pieces being attached to the steel structure in places around the edge of the building, there are two levels of flats built from the metsec. 

throughout the corridors we are running galv tray containment, which is fixed to ceiling beams of metsec. 

Walls will be lined with two layers of plasterboard. 

There is also Gas being run into flats, incoming in standard yellow plastic pipe then Copper through to each flat. 

So given that that all the steel and metsec is joined/continuous metal here’s my issue. 

1) Normally bonding would be taken to each gas pipe into each flat from flat DB, but should this gas pipe be attached direct to metsec then each flat bond will bond all other metalwork to flats and beyond. 

Is this correct? 

2) should we apply an additional local bond in each flat to the metsec? 

3) a fault in one flat may have effect on others? 

4) similarly will a lightning strike have an effect within each flat? Understand that the lightning will take path of least resistance but will the metal structure be affected by a strike? 

Spoke to IET technical who say that it depends on the design of lightning protection system? I’m told that the lightning protection system is separate to the steel structure all be it runs down it on the insulation pads. 

Thoughts please. 

 

[Evans Electric]

This is interesting,  because of all that metalwork  any spark would be getting a bit wary .  

I was always concerned and somewhat surprised when I read that the lightening conductor would now be connected to the MET   .   I've been out of new build commercial for a while now  so can offer no expertise,  not seen it done . ...sounds mad to me. .  

You have to bond the gas as you say ,  in each dwelling and if its bolted to the steel structure then you are also connecting the steel work to the incoming neutral .

Did you say it was a PME suppy  ?   

Getting back to basics ....all that metalwork needs to be at the same potential  so you need multiple bonds I imagine .....but I'm thinking the DNO won't be supplying PME  to a , basically , metal box.  

Interested to see what the great minds have to say . 

 

[Sharpend]

Well that's the thing, I believe that the supply is said to be TNCS?

 

[binky]

lighting conductor should be bonded at incommer, last time I looked at such things.  I think Evans is probably right in that more bonds the merrier to bring potential on all metal work to same voltage asap, Faraday cage principle, thoigh waht ruddy size I have no idea.

 

[Sharpend]

Well this is the norm now with lightning protection systems, they have their own rods to which the tapes are attached, however now you have to take an earth cable out to one of the tapes, they then fit a surge arrestor device at the incomer. 

I was more concerned as to whether a fault in one flat would be shared/replicated in all others? Would this be considered safe or correct? Normally each flat is treated as it's own installation and therefore individually subject to the regs re bonding.

 

[Sidewinder]

Does each flat have it's own MPAN number?

 

[Sharpend]

Does each flat have it's own MPAN number?

Yes

 

[ProDave]

You have to bond the gas as you say ,  in each dwelling

Doesn't 18th say NOT if it's PLASTIC?

(even if it does I bet the gas regs have not or will not be updated so will be in conflict)

 

[Sharpend]

But even if I don't bond the gas, the gas pipe is still fixed to the metsec? 

 

[Evans Electric]

There is also Gas being run into flats, incoming in standard yellow plastic pipe then Copper through to each flat. 

Some members picked me up on this a few weeks ago but I still maintain that you HAVE to bond the copper in each unit   ( Even though it is NOT introducing an external earth  being yellow PVC)   )    The whole point was to create the cage within each dwelling  / house / flat .      

 

[Sharpend]

Buts that fine in individually separated but does it stand the same for one large cage housing individual properties?

 

[Evans Electric]

Well I'm just repeating what the NIC say  with each flat  fed with ..say.... a common copper water pipe  ,  on the face of it you'd think  one main bond  covers all  but no ,...its each unit bonded as per normal .

Without delving into the regs I'm sure that on a building like that there will be a main bond onto the steelwork  , at the mains somewhere .  So steelwork will be at earth potential ....copper gas pipe  could be floating  in each flat  so needs bonding , water could be the same with all the PVC  sections .  

 

[binky]

the regs still seem to trest an individual household and an individual unit to be treated accordingly. If the gas pie is bonded and connected to metal work, it just means it has far more earthing paths. If you test a mormal house the parallel earth paths are 'surprisingly conductive'.

 

[Sharpend]

My thoughts were originally that the gas would need bonding, then I thought about the metsec walls and the similar setup of metalstud frames when the young mother was killed whilst mopping the floor when water seeping under the skirting and touching the metal which happened to be live due to a fault?

 

[Sharpend]

the regs still seem to trest an individual household and an individual unit to be treated accordingly. If the gas pie is bonded and connected to metal work, it just means it has far more earthing paths. If you test a mormal house the parallel earth paths are 'surprisingly conductive'.

I'm aware of this, but believe that they are referring to standard built dwellings, not a metallic structure which encompasses all dwellings?

the IET tech guy was thinking that all metal should be bonded but then took a rain check and decided that it was a lot more complicated than that, adding in the lightning system and fully metallic structure which is continuos through whole building. 

 

[Sidney]

I would bond the utilities as normal within each property and also the building fabric. Basically bringing the whole property to the same potential.

Under fault conditions there is the potential for the whole system to become live however with the size of the building and it's construction tied in with lightning protection the touch voltages would be minimal for a very short duration. Not forgetting nearly everything will normally be put on some form of RCD.

As for the LP, as long as the building services have surge protection at each point of entry then I can't see any issues. Also I would consider adding SP to each flat DB to create their own zones within the building.

 

[Evans Electric]

Yes  I think that stays with all of us TBH.      IN West Bromwich I believe. 

From what was finally disclosed it  sounded like the metal stud verticals  were NOT earthed / bonded  ......a  plasterboard screw pierced the live of  a Twin / E    thus making the studding live from day one ......   all that about the testing  ...no one would have picked it up UNLESS  they took the time to test between  the L of the circuit and the HIDDEN screws  in the plasterboard .      

I don't know about the RCD situation .....and yes ...  it shouldn't have happened .........every time I see metal studding I think of this case  and the family involved.  

 

[Sharpend]

Now there will be two supplies into the building, one for the shop and one for the flats, I am hoping that his has been taken into account wrt LP as they normally provide the surge protection of main incoming supply. I suppose in this instance that individual SA to the flats would cover all eventualities?

 

[Evans Electric]

Sharpie ... is there not a design  element on this project ?   A huge amount of our work in the past was under the design of local consultants  and such things are  sorted by them , as you know .

They don't always get it right .  We did a major referb on a bank  ....consultant specified a new  mains panel in the basement ...the main switch being a 200A   TPN  100mA   RCD   :C          I went there to find a fault on a door heater , suspected a phase was out , put my test lamps across  blue phase  & earth  and the whole branch went off ....staff into "Bandit" mode ...police cars screaming up to the door.  :C

 

[Sharpend]

Well that's the thing Deke, the design element doesn't seem to be filtering down, so I've bounced it back, now waiting on their feedback. The guy I'm subbing too, is adamant that I should just bond everything, I'm just wary that not only are the flats all individual dwellings but there is also the shop and given that there are two separate supplies into a single steel structure covering all premises???