To bond or not to bond, that is the question

Let me paint a picture....

An industrial estate with 10 - 15 small units of similar construction. Single storey, brick and block build with trapezoidal sheet roofs that round off front and back to give a top hat effect raising the roofline higher that brick courses.

Roof sheets supported by your standard galv steel purlin. Built about 20 years ago I'd say and all owned / let out by one company.

All the above is well out of reach!

Each unit has a single wooden door for foot access and a roller shutter door for goods in and out. Here is were it gets tricky. The guides (metal) for the roller shutter door are fixed to 2 of the purlins and then come down and bolt into the concrete pad (floor).

None of the units seem to have a bond to the roof / purlins. We took Mr NIC to one as an inspection job and he gave us a N/C for 1) not picking up that it wasn't bonded. Job was a EICR. His arguement was that the 'structural' steel was being transposed into reachable grounds by the roller shutter guides....

So, we inform the letting company who state that no other reports have ever mentioned it.

So, the big question is, does it need bonding???

If it does then lack of main bond is C2 and so an unsatisfactory report?

Discuss!

if the steel goes into the ground then its most likely extraneous, if its common to next door then it could introduce a potential and so would be extraneous and would need bonded. so yes, it most likely needs bonded and would be C2

As Andy said. If is it bolted to the ground, then it is most likely extraneous. As Andy ALSO said, if it is common to next door, it could also introduce a potential. If something conductive does "go next door" the potential that could be introduced to YOUR area might not just be earth potential, or even a differing earth potential, but it could be at anything up to full mains voltage if there is a fault...

As well as this, it could introduce a potential even if there is no fault whatsoever.

Imagine that you and next door are both on TNCS. Your metal work is bonded to your MET, and their metal work is bonded to their MET. You are nearer to the mains in the street then them and therefore your neutral has a lower impedance than theirs. You touch their metal work AND yours, and YOU are now part of, [in parallel with] their neutral.... Oooeerrrr...

john..

apprentice87 said:

As Andy said. If is it bolted to the ground, then it is most likely extraneous. As Andy ALSO said, if it is common to next door, it could also introduce a potential. If something conductive does "go next door" the potential that could be introduced to YOUR area might not just be earth potential, or even a differing earth potential, but it could be at anything up to full mains voltage if there is a fault...

As well as this, it could introduce a potential even if there is no fault whatsoever.

Imagine that you and next door are both on TNCS. Your metal work is bonded to your MET, and their metal work is bonded to their MET. You are nearer to the mains in the street then them and therefore your neutral has a lower impedance than theirs. You touch their metal work AND yours, and YOU are now part of, [in parallel with] their neutral.... Oooeerrrr...

john..

Click to expand...

They ARE TNC-S supplies, so are you saying it would be bad to bond to MET?

Must be bonded.

The steel is structural, thus in intimate contact with the floor.

That is, unless you can prove that it is not extraneous at that point of the test with the23k(?, I can never remember the value, I always have to look it up, test), value

Check with DNO if they will allow multiple connections in one portal steel unit to TN-C-S supply.

Letting company is wrong.

Full stop, end of story.

Makes you wonder why it has never been brought up before...

'only gas & water need bonded'

Andy™ said:

'only gas & water need bonded'

Click to expand...

Yeah, they were done

Sidewinder said:

Must be bonded.

The steel is structural, thus in intimate contact with the floor.

CORRECT..

That is, unless you can prove that it is not extraneous at that point of the test with the23k(?, I can never remember the value, I always have to look it up, test), value

25K usually or 50K if it is an area where people are likely to have wet skin bare feet etc

Check with DNO if they will allow multiple connections in one portal steel unit to TN-C-S supply

They do not!!!

Click to expand...

john...

Barx said:

Makes you wonder why it has never been brought up before...

Click to expand...

Has, many times..

john..

Barx said:

They ARE TNC-S supplies, so are you saying it would be bad to bond to MET?

Click to expand...

It would be even more important to bond than usual.

Imagine if next door have a neutral fault in their service joint??? Any steelwork connected to THEIR MET [and poking into YOUR unit] is now live at anything up to full mains voltage. What do you suppose will happen if you touch it??

If there is metalwork shared between different units in the same building the DNO will ONLY TNCS the one, and the others will be told to TT theirs..

You need to contact the DNO. There are other SERIOUS problems that can occur too....

john..

apprentice87 said:

Has, many times..

john..

Click to expand...

Cheers John

I just meant why it's not been brought to the letters attension

Barx said:

Cheers John

I just meant why it's not been brought to the letters attension

Click to expand...

Simple, on here there are some genuinely clever blokes, unfortunately not all the people who do inspect and test are clever, a lot of them lack basic understanding. A few years ago I was shown a report for my doctors surgery, it had failed for the following reasons, 1/ main earth bonds undersized, 2/ consumer unit with rewireable fuses, 3/ two sockets on a spur.

Point one, the place was wired to an earlier version of the regs, it was originally a private bungalow and is now the village doctors surgery, wired when 6mm to gas and water was the norm, and the system is still fine. point 2, there is nothing wrong with fuses, if the board is sound no need to replace it, and most interestingly point 3, the "spur" in question was actually a radial fed from a 15A fuse, it was installed solely to feed 2 computers.

There is such a thing as "good for continued service", something a lot of these clowns don't understand, it actually states somewhere that if a premise was wired to an earlier version of the regs then you inspect as such, not basing it just on the current version. I can't wait for a few years down the line, all the houses that were built just before amendment 3 came out and have plastic CU's fitted, these clowns will be going round telling people their install doesn't comply because it has a plastic board!

phil d said:

Simple, on here there are some genuinely clever blokes, unfortunately not all the people who do inspect and test are clever, a lot of them lack basic understanding. A few years ago I was shown a report for my doctors surgery, it had failed for the following reasons, 1/ main earth bonds undersized, 2/ consumer unit with rewireable fuses, 3/ two sockets on a spur.

Point one, the place was wired to an earlier version of the regs, it was originally a private bungalow and is now the village doctors surgery, wired when 6mm to gas and water was the norm, and the system is still fine. point 2, there is nothing wrong with fuses, if the board is sound no need to replace it, and most interestingly point 3, the "spur" in question was actually a radial fed from a 15A fuse, it was installed solely to feed 2 computers.

There is such a thing as "good for continued service", something a lot of these clowns don't understand, it actually states somewhere that if a premise was wired to an earlier version of the regs then you inspect as such, not basing it just on the current version. I can't wait for a few years down the line, all the houses that were built just before amendment 3 came out and have plastic CU's fitted, these clowns will be going round telling people their install doesn't comply because it has a plastic board!

Click to expand...

They are doing that already Phil,  heard a comment in the wholesalers recently.  Some 12 yr old sparky saying he went to wire a shower ...AND THE BOARD WAS PLASTIC !!!  oOMG!!!    How he kept control of his bowells I'll never know !     Imagine that , a plastic board. :C

Thing with testing for EICR 's  , as far as I know , and others have said it on here,   we are supposed to inspect to the latest regs so things like  6mm bonding crop up all the time .

Trouble with that is , as we know,  the Rules Regs change every  3 weeks. 

I'm looking at some work thrown up by an insurance EICR  at a company I do a lot for ,  most of the socket circuits (14th edition) said to need RCDs   ( 17th edition/ Amd3) .

Previous Regs said sockets under control of trained persons etc etc ............thats gone now so they're looking at some hundreds of £££s worth of RCBOs , some boards won't accept them ...so .  

Put an RCD in a separate enclosure downstream of the DB treat it as a lolipop circuit if it is a ring.

Lavk of RCD in that scenario is only a C3 anyway.

They've gone with C2s  on the RCds  and yes I've quoted for remote enclosures .  

Most of what they've put is fair comment really , couple of old Bill boards , 3036...flash shields missing...asbestos linings & doubled up circuits .  I've been telling them for the last 20 years but theres a new director now who sees his head on the line in the H&S side of things .     I think he'll ge with changing these during the next slack period ..its printing all school books at the moment, hectic.  

phil d said:

 it actually states somewhere that if a premise was wired to an earlier version of the regs then you inspect as such, not basing it just on the current version.

Click to expand...

you always I&T to the current version, but that doesnt mean if it was wired to previous that its now suddenly dangerous

and you can still have a 6mm bond to todays standards...

Andy™ said:

you always I&T to the current version, but that doesnt mean if it was wired to previous that its now suddenly dangerous

and you can still have a 6mm bond to todays standards...

Click to expand...

I stand corrected.

Presence of asbestos alone is a C2.

Bring back C4......and not the faintly almondy smelling one

Evans Electric said:

They are doing that already Phil,  heard a comment in the wholesalers recently.  Some 12 yr old sparky saying he went to wire a shower ...AND THE BOARD WAS PLASTIC !!!  oOMG!!!    How he kept control of his bowells I'll never know !     Imagine that , a plastic board. :C

Thing with testing for EICR 's  , as far as I know , and others have said it on here,   we are supposed to inspect to the latest regs so things like  6mm bonding crop up all the time .

Trouble with that is , as we know,  the Rules Regs change every  3 weeks. 

I'm looking at some work thrown up by an insurance EICR  at a company I do a lot for ,  most of the socket circuits (14th edition) said to need RCDs   ( 17th edition/ Amd3) .

Previous Regs said sockets under control of trained persons etc etc ............thats gone now so they're looking at some hundreds of £££s worth of RCBOs , some boards won't accept them ...so .  

Click to expand...

That was another point raised in same place. Socket outlets 'could' be used for outdoor equipment (so could any other, in any building, if you tried hard enough). Should have been a C2 and so again an unsatisfactory report.

Tested continuity from above mentioned roller shutter guide to MET on one today. 19 ohm :facepalm: