Main bonding conductors connected to trunking.

[AdamKerr88]

Today i have been asked to give an independant opionion on electrical work undertaken by another electrician on a commercial property.

There has been work done to "improve the mains bonding arrangments".

The buildings supply is a 100a 3 Phase TN-C-S. Connection to this is by a 50mm2 single, crimped and bolted to the side of the cut-out connecting to a small domestic 8 way MET. There is then a 16mm2 cpc supplying the D.B which is fed from a 100x100 trunking between the supply and the D.B.

Before the work was carried out there was 2 x 10mm2 singles connecting the MET to the incomming gas service. He has now cut these back, crimped and screwed them to the side of the 100 x 100 trunking. Surely this has only made the situation worse ??

543.2.2 does say that a metalic cable management system can be used as a protective conductor but surely not for mains bonding as this must be connected directly to the MET?

This is by no means the only issue here, however i dont want to list "Protective bonding conductors not connected directly to the MET" if this is not actually incorrect.

Thanks

 

[Guest55]

youre right.
main bonds should be continuous and unbroken en route to the services.
only cpc's can use metal containment as a carrier.
i'd give it only a code 3 defect on an inspection to be fair though.

 

[daiplayer]

surely bonding should from services straight to met.
less than 0.05 ohms ? doubt it

 

[johnboy6083]

I doubt that the steel trunking has enough CSA to meet the requirements as a bonding conductor. It's common practice to use exposed metalwork as a bonding conductor. It's usually structural steelwork though, as that is very unlikely to be removed. I don't like the idea of using trunking as a bonding conductor, especially in a PME scenario, as if the supply neutral is lost, then the trunking would probably get warm, and possibly overheat the cables inside.

 

[Chr!s]

youre right.
main bonds should be continuous and unbroken en route to the services.
only cpc's can use metal containment as a carrier.
i'd give it only a code 3 defect on an inspection to be fair though.

He's not, Mains bond don't need to be continuous, old wive tale that one.

 

[Chr!s]

I doubt that the steel trunking has enough CSA to meet the requirements as a bonding conductor. It's common practice to use exposed metalwork as a bonding conductor. It's usually structural steelwork though, as that is very unlikely to be removed. I don't like the idea of using trunking as a bonding conductor, especially in a PME scenario, as if the supply neutral is lost, then the trunking would probably get warm, and possibly overheat the cables inside.

100 x 100 copper equivalent = 40.2mm and i doubt heat would be an issue in a PME scenario, no insulation.

 

[Guest55]

He's not, Mains bond don't need to be continuous, old wive tale that one.

i cant think of a single benefit from changing a continuous conductor into a conductor interupted by containment connections thus introducing more opportunities for a break in continuity.
its certainly not what i consider an "improvement in earthing arrangements"

 

[johnboy6083]

I agree that the lack of insulation will aid in heat dissapation, but if cables inside the trunking are at full capacity, and therefore at max operating temp, then I feel that a few installations worth of neutral current could cause a problem.

 

[AdamKerr88]

i cant think of a single benefit from changing a continuous conductor into a conductor interupted by containment connections thus introducing more opportunities for a break in continuity.
its certainly not what i consider an "improvement in earthing arrangements"

Thats exactly it ! Its only made it more likely to be broken at some point. Also the trunking is not connected to the MET other than its connection to a metal db.

 

[daiplayer]

He's not, Mains bond don't need to be continuous, old wive tale that one.

needs to be continous if one bonding conductor is used for two services .

 

[jumpin jax]

needs to be continous if one bonding conductor is used for two services .

That also i believe is advisory too

 

[Guest55]

Also the trunking is not connected to the MET other than its connection to a metal db.

well it is connected to the MET if the trunking forms part of the main bonding ?

Does the trunking earth fixing bolts have "safety electrical connection" tags that you find on pipe clamps ?
if not you can code it on that alone ;-)

 

[AdamKerr88]

well it is connected to the MET if the trunking forms part of the main bonding ?

Does the trunking earth fixing bolts have "safety electrical connection" tags that you find on pipe clamps ?
if not you can code it on that alone ;-)

Sorry was'nt too clear with that......

It connects to the trunking instead of the MET.

 

[Chr!s]

surely bonding should from services straight to met.
less than 0.05 ohms ? doubt it

Why?

i cant think of a single benefit from changing a continuous conductor into a conductor interupted by containment connections thus introducing more opportunities for a break in continuity.
its certainly not what i consider an "improvement in earthing arrangements"

In a commercial/Industrial scenario you will find many a connection through out the length of the Main Bonding

I agree that the lack of insulation will aid in heat dissapation, but if cables inside the trunking are at full capacity, and therefore at max operating temp, then I feel that a few installations worth of neutral current could cause a problem.

And you think these conductors will be operating at Max temp with a broken pen? Will all equipment be operating under fault conditions?

Thats exactly it ! Its only made it more likely to be broken at some point. Also the trunking is not connected to the MET other than its connection to a metal db.

Well, who ever is carrying out work on any installation needs to be competent to do so, you cant design a fortress.

needs to be continous if one bonding conductor is used for two services

Say's where

Does the trunking earth fixing bolts have "safety electrical connection" tags that you find on pipe clamps ?
if not you can code it on that alone ;-)

I suggest you read the reg on that one


Your the inspector, its for you to decide as to whether the installation is designed and installed correctly, Trunking can be used as Main Bonding, is it designed and installed correctly, that's your call.

 

[Engineer54]

And there was me thinking that metal trunking/tray containment systems always use at least 2 copper bonding links between bolted sections!!!!

 

[Chr!s]

And there was me thinking that metal trunking/tray containment systems always use at least 2 copper links between bolted sections!!!!

Not on the new stuff E54, unless you don't trust what the manufactures say that is.

 

[Deleted member 26818]

And there was me thinking that metal trunking/tray containment systems always use at least 2 copper bonding links between bolted sections!!!!

No just the one.

 

[Engineer54]

Not on the new stuff E54, unless you don't trust what the manufactures say that is.

No just the one.

Always used a minimum of two, (one on each side of the butted sections) that was the norm, and as far as i'm concerned, still the norm on metal containment systems no matter what the manufacturers say. But then I suppose these days, even retaining one copper link is something of a miracle!! lol!!

Do they still call for 2 copper bonding links placed at diagonal corners across non metallic expansion joints on A/C ductwork, or has that gone by the board as well??

 

[kingeri]

Is that a bit like bonding across compression fittings on copper pipework?

 

[Deleted member 26818]

Always used a minimum of two, (one on each side of the butted sections) that was the norm, and as far as i'm concerned, still the norm on metal containment systems no matter what the manufacturers say. But then I suppose these days, even retaining one copper link is something of a miracle!! lol!!

Do they still call for 2 copper bonding links placed at diagonal corners across non metallic expansion joints on A/C ductwork, or has that gone by the board as well??

Whilst the straight sections of trunking could have a link either side, the bends and sets only have a knock out hole (usually with an earth adjacent), on the one side.
If you wanted to add another link, you would have to drill a hole, which would suggest that only the one link is deemed as being necessary.

No there doesn't appear to be a requirement for bonding across expansion joints in A/C ductwork.

 

[Engineer54]

Whilst the straight sections of trunking could have a link either side, the bends and sets only have a knock out hole (usually with an earth adjacent), on the one side.
If you wanted to add another link, you would have to drill a hole, which would suggest that only the one link is deemed as being necessary.

No there doesn't appear to be a requirement for bonding across expansion joints in A/C ductwork.

That i would have thought, would be standard practice, when fabrication of sections are required on metal containment systems??

Why did i know that was going to be the feed back, on the A/C ductwork... lol!!

 

[D Skelton]

Always used a minimum of two, (one on each side of the butted sections) that was the norm, and as far as i'm concerned, still the norm on metal containment systems no matter what the manufacturers say. But then I suppose these days, even retaining one copper link is something of a miracle!! lol!!

Do they still call for 2 copper bonding links placed at diagonal corners across non metallic expansion joints on A/C ductwork, or has that gone by the board as well??

I suppose this all comes down to how you were taught. I only found out recently that you need not link between joints in metallic containment systems or A/C ductwork, but I always have and will continue to do so! 2 links in my mind would be a little overkill but again, it comes back to what you were taught and also what you're comfortable with.

 

[Guest55]

In a commercial/Industrial scenario you will find many a connection through out the length of the Main Bonding

Yes but its designed like that to begin with , not retro bodged at a later date from what was a superior arrangement.

Well, who ever is carrying out work on any installation needs to be competent to do so, you cant design a fortress.

Well a continuous conductor from a to b is fairly bombproof.

...................

 

[Chr!s]

...................

We don't know if it's a bodge, it well be fine, you can't code it just because you don't like the idea.

The continuous conductor with to connections one at either end.

 

[Guest55]

We don't know if it's a bodge, it well be fine, you can't code it just because you don't like the idea.

i'm sure i'll find something to code if i looked hard enough.
the contractor seems suspect if these are his recommended "improvements"

The continuous conductor with to connections one at either end.

Is fundamentally better than one with additional connections in the middle , that already existed in the first place

You can throw in as many technical counter-points as you like but....
a bad idea , that just happens to comply with bs7671 , probably by sheer good luck , is still a bad idea.
;-)
you must of course think it a great idea following your rigorous defence of this "improvement" ?
:-D

 

[shoddyboby]

:61:hi all am new jus posting to start up my account

 

[MarkieSparkie]

Yes E54, that's the way we were trained back in the day mate, when the standard of British workmanship was valued, these days it seems that monkey spit and high hopes are good enough; well not for me... do it once, do it right!

 

[Chr!s]

You can throw in as many technical counter-points as you like but....
a bad idea , that just happens to comply with bs7671 , probably by sheer good luck , is still a bad idea.
;-)
you must of course think it a great idea following your rigorous defence of this "improvement" ?
:-D

We have been using Trunking as a Protective conductor for years, installed correctly its a good system the same as any other, Trunking as a protective Conductor a bad idea? No i don't think so.

Improvement? Well it maybe, why has he done it? Maybe he knows what he is doing and there is no "sheer good luck" to do with it, just a good competent electrician.

AS for further codes, here are your first two.

youre right.
main bonds should be continuous and unbroken en route to the services.
only cpc's can use metal containment as a carrier.
i'd give it only a code 3 defect on an inspection to be fair though.

Incorrect

well it is connected to the MET if the trunking forms part of the main bonding ?

Does the trunking earth fixing bolts have "safety electrical connection" tags that you find on pipe clamps ?
if not you can code it on that alone ;-)

Incorrect


So two codes you have given are incorrect, third time lucky maybe?

As i said you need to be competent.

 

[Guest55]

We have been using Trunking as a Protective conductor for years, installed correctly its a good system the same as any other, Trunking as a protective Conductor a bad idea? No i don't think so.

i never said using trunking for earthing was a bad idea but changing it from a continuous , dedicated conductor that already existed is a good idea ?



Improvement? Well it maybe, why has he done it? Maybe he knows what he is doing and there is no "sheer good luck" to do with it, just a good competent electrician.

we'll never know without looking at the job will we ?



AS for further codes, here are your first two.



Incorrect



Incorrect


So two codes you have given are incorrect, third time lucky maybe?

ooh thats so cruel , good job i'm thick skinned.
i conceed my mistakes on those 2 points , touche.




As i said you need to be competent.

.............

 

[Chr!s]

I do apologise Biff, no cruel intention, a poor post, must do better