connections of cpc

[LeeH]

Thanks, I have that and embarrassingly have used the SWA table.....

 

[Engineer54]

Well, if you just take a properly installed 20mm conduit containment system, it's giving you the equivalent of 10mm of a copper CPC (minimum)!! No contest in my book!! lol!! So why would anyone then go and fill that 20mm conduit with separate CPC's??

 

[sparks1234]

Explain to me what you don't like about a full metal containment system being the CPC for the circuits it's supplying??

Nothing old school about it, apart from being used for far more years than anyone here can remember, ....Why, because it works and works better than containment filling individual circuit CPC's!! The project i'm working on now, along with every other major project i've worked with, that has extensive metal containment systems throughout, have never included separate circuit CPC's.

I'd put bet's on, that the Zs values that i'm used to seeing, are far superior than anything you would typically expect to see!!

Eng 54

I would agree with you that they can give much better Zs values
The problem can come when installations get older and perhaps deterioration between joints causes problems, the other thing I have seen is when alterations are made and then the trunking is not put back as it should.
I would agree with you in a perfect world that a containment system properly installed works well but as we have probably all seen the links are often not put back on or incorrectly
Also the junction between trunking/ conduit can be a problematic area
I would also disagree with you that its not old school, as you said, its donkeys years old and I would suggest the majority of sparks would install a suitable cable as CPC for each circuit

 

[Engineer54]

Well i can show you hundreds if not thousands of metal containment systems that are nearly as old as me, that will still give superior Zs values without a single separate CPC in sight!!

It has nothing to do with the perfect world scenario you imply, but everything to do with installation tradesmen installing metal containment systems correctly/properly. No, junctions between trunking and conduit do not cause problematic areas if they are made correctly in the first place. I bet you have never seen a high current metal containment system test set that can/will prove every metal to metal connection on the system, section by section!! You also do not base an installation method on what may or may not happen in the future, or on incompetent persons making non compliant alterations. There has been no better rewirable containment system (depending on the environment) than metal containment systems. They provide excellent mechanical protection, electrical protection (Zs values), lifespan expectancy, and a good few more real advantages over other containment systems to boot.

Seeing as many electricians these day's have never installed and i think i would be right in saying are not even capable of installing a metal containment system, they would know no better. Basically it comes down to asking, what fool would fill up a metal conduit with CPC's, when the containment itself is far bloody superior than the combined separate CPC's??

As i have stated previously, i have NEVER installed separate CPC's on ANY of the the projects i've been involved with ''Including'' my present project, and more importantly it has never been requested/required in any of the contract electrical specifications. Obviously you never electricians think you know better than us, ...but i put it to you, that past T&E, SWA, plastic containments and the like, you know very little!! And i'm not blaming the individuals, i put the blame firmly into the consistant lowering of our industries education standards....

 

[sparks1234]

Well i can show you hundreds if not thousands of metal containment systems that are nearly as old as me, that will still give superior Zs values without a single separate CPC in sight!!

It has nothing to do with the perfect world scenario you imply, but everything to do with installation tradesmen installing metal containment systems correctly/properly. No, junctions between trunking and conduit do not cause problematic areas if they are made correctly in the first place. I bet you have never seen a high current metal containment system test set that can/will prove every metal to metal connection on the system, section by section!! You also do not base an installation method on what may or may not happen in the future, or on incompetent persons making non compliant alterations. There has been no better rewirable containment system (depending on the environment) than metal containment systems. They provide excellent mechanical protection, electrical protection (Zs values), lifespan expectancy, and a good few more real advantages over other containment systems to boot.

Seeing as many electricians these day's have never installed and i think i would be right in saying are not even capable of installing a metal containment system, they would know no better. Basically it comes down to asking, what fool would fill up a metal conduit with CPC's, when the containment itself is far bloody superior than the combined separate CPC's??

As i have stated previously, i have NEVER installed separate CPC's on ANY of the the projects i've been involved with ''Including'' my present project, and more importantly it has never been requested/required in any of the contract electrical specifications. Obviously you never electricians think you know better than us, ...but i put it to you, that past T&E, SWA, plastic containments and the like, you know very little!! And i'm not blaming the individuals, i put the blame firmly into the consistant lowering of our industries education standards....

Youre not actually taking in what I've written
i agree with you on the principal
unfortunately most of use do not live in the perfect world and work with clients that don't have unlimited budgets
i have no idea if you work for government or private sector but quite honestly it's not any hassle pulling a cpc through
at least then you can be fairly sure your earth is in and continuous
some people don't realise the containment system is doing more than a mechanical protection job
i have over the years come across various installation that have containment systems where the continuity has broken down so if it's easy enough to do then why take the risk?

 

[Lucien Nunes]

E2A did not see above post, agree with Sparks1234, it's all about horses for courses.

Metallic containment can provide a nice low impedance CPC and depending on the layout can offer multiple redundant paths and therefore improved reliability. But there are certainly situations where the latter does not apply and the number of joints moves you in the other direction towards decreased reliability, compared to an unbroken run of copper cable.

I have seen single conduit runs with 100 joints used as CPC, but one would think it poor practice to include 50 times as many connections in series as necessary, compared with using a cable. I have done battle in inconvenient places with well-made, sound-looking and tight steel conduit connections that were nonetheless high-resistance or even open-circuit, so it is not a hypothetical situation.

As for earth terminal blocks in trunking, I would think the risk of damage to other cables while working on those connections sufficient to throw a C3 at it. Also if there are supplies in there fed from other boards that would have to be isolated for safe working, that otherwise could be left alive if the terminals were in the DB or separate box.

 

[Engineer54]

Couldn't disagree with you more, a metal conduit system that has been installed and erected correctly by skilled tradesmen, will not decrease in reliability. I was brought up, or should i say dragged up on industrial metal containment systems, never seen one go bad, except where environmental conditions hadn't been taken into account, or the environmental useage of the area's conditions had changed. As stated previously, any signs of suspect joints and/or connections will show up like a sore thumb when initially tested with a high current ohm meter.

Not sure what you're saying here, are you saying that metal containment should be restricted to X amount of screwed connections?? That'll be a new one on me...

Why fill say a 20mm conduit system carrying maybe 3 circuits with 3 unnecessary CPC's?? It was never necessary in the past and it's not necessary now!! You're going to have to go some, to lose the equivalent of 10mm of copper on a 20mm conduit system. Never installed a CPC in metal containment and have no intention of ever doing so. ....Money straight down the drain!! ... lol!!

 

[sparks1234]

Couldn't disagree with you more, a metal conduit system that has been installed and erected correctly by skilled tradesmen, will not decrease in reliability. I was brought up, or should i say dragged up on industrial metal containment systems, never seen one go bad, except where environmental conditions hadn't been taken into account, or the environmental useage of the area's conditions had changed. As stated previously, any signs of suspect joints and/or connections will show up like a sore thumb when initially tested with a high current ohm meter.

Not sure what you're saying here, are you saying that metal containment should be restricted to X amount of screwed connections?? That'll be a new one on me...

Why fill say a 20mm conduit system carrying maybe 3 circuits with 3 unnecessary CPC's?? It was never necessary in the past and it's not necessary now!! You're going to have to go some, to lose the equivalent of 10mm of copper on a 20mm conduit system. Never installed a CPC in metal containment and have no intention of ever doing so. ....Money straight down the drain!! ... lol!!

lol
youre totally missing the point
certain circumstances steel conduit and trunking deteriate
i wouldn't rely on it in many situations in normal run of the mill jobs, rust does get in, that's the nature of steel
youre comment on not allowing for future alterations is short sighted to say the least
but hey ho

 

[Lucien Nunes]

One has to be pragmatic - no equipment, material or technique is infallible. If everything is in good order then I agree that metal containment is a durable and effective CPC. But electrical systems erected commercially to a realistic budget and subjected to normal non-domestic usage, are likely to contain imperfections in cables, containment, switchgear and accessories. Some of those will be deterioration of weak spots created during installation, some will be random accidental damage, some deterioration due to age. Amongst them will be loose and high resistance joints in containment.

In certain circumstances, such as the long tortuous conduit runs I described, adding a copper CPC could provide a worthwhile increase in CPC integrity, justifying its modest cost. In others, such as multiply-interconnected trunking grids, I am fully in agreement that adding a cable would serve no useful purpose either to decrease impedance or increase reliability.

 

[sparks1234]

for godsake dont knock eng or he'll turn on u

Yep, did that for sure. Lol

 

[Engineer54]

lol
youre totally missing the point
certain circumstances steel conduit and trunking deteriate
i wouldn't rely on it in many situations in normal run of the mill jobs, rust does get in, that's the nature of steel
youre comment on not allowing for future alterations is short sighted to say the least
but hey ho

I'm not missing the point at all, metal containment systems do NOT require/need separate CPC's.
As i've indicated previously, if a metal containment system has been skillfully erected, using the proprietary conductive sealing paste to all screwed connections and the proprietary zinc paint to any exposed thread on a system suitable for the environment it is installed within, severe deterioration should not be a problem.

Allowance for future additions and alterations, is not afforded to individual circuit conduit runs, that is normally afforded to DB's and the like. Start going down those lines and the installation is going to get very expensive very quickly. With trunking, you have in most instances, an inherent means of easily accommodating additions and alterations. Just wondering how you allow for incompetent persons undertaking any such work in the future

Further, i personally i haven't used solid core single cables in conduit, they are just not suitable or fit for purpose, being pulled into tube as far as i'm concerned, even less so when additional cables are pulled into an existing conduit system, stranded cables are by far, more accommodating all round!! I don't allow inspection bends and Tee's either, those bloody things rip cable insulation to shreds!!

One has to be pragmatic - no equipment, material or technique is infallible. If everything is in good order then I agree that metal containment is a durable and effective CPC. But electrical systems erected commercially to a realistic budget and subjected to normal non-domestic usage, are likely to contain imperfections in cables, containment, switchgear and accessories. Some of those will be deterioration of weak spots created during installation, some will be random accidental damage, some deterioration due to age. Amongst them will be loose and high resistance joints in containment.

You could say that 99.99% of all metal containment systems will fall outside of domestic usage!!
Yes, you may well get some weakness in a few screwed connections etc, during installation but again, they will show up like a sore thumb under high current testing. As for random accidental damage during the life of the installation, one would expect that any damage to an electrical containment system would be corrected, ...again by skilled electricians..


In certain circumstances, such as the long tortuous conduit runs I described, adding a copper CPC could provide a worthwhile increase in CPC integrity, justifying its modest cost. In others, such as multiply-interconnected trunking grids, I am fully in agreement that adding a cable would serve no useful purpose either to decrease impedance or increase reliability.

On long tortuous conduit runs the size of the conductors would probably need to increase, and possibly the size of the conduit to accommodate the larger conductor sizes. But again, you would really need to go some, before that 10mm or more of equivalent copper conductor would be lost or need reinforcing by far smaller separate CPC's...

Yes, some metallic conduit systems have been erected in unsuitable environmental conditions, and may well prematurely deteriorate. But then surely that installation would need to be replaced rather than try to fluff around with it, while still deteriorating further??

 

[Lucien Nunes]

I suspect we are reaching different conclusions based on different local conditions and parameters. I have regular contact with old installations in which considerable deterioration has occurred. Many of our new installations are replacements of these, which I expect will be subjected to similar circumstances and likely to deteriorate albeit perhaps not to the same extent, before reaching a maintenance equilibrium. Loose conduit and trunking joints are fairly commonplace in the existing and I would be dishonest if I claimed that they would never occur in our work throughout its life.

Whilst I would like to think that the workmanship will be uniformly excellent and more permanent and durable than the work of mr. average electrician, in practice there are men up towers in a theatre at this moment installing metal containment for us whose personal trials and tribulations that could lead to a loose coupler or a forgotten backnut I do not know, and I am not going to inspect every inch personally. The job will be sound and compliant overall, however I very much doubt that every joint will be tested with a Ducter, again unless I do it myself.

BATNEEC (best available technique not entailing excessive cost) suggests we should bolster likely weak spots in the containment continuity, for the specific reason that it is often inexpensive. Again here our circumstances might differ. I might have 16 circuits in one enclosure and 8 enclosures on one system of containment, all of which would be reliant on a string of trunking joints for CPC. I can provide a copper CPC to each enclosure for a total cost of perhaps £40, in which all 128 circuits become independent of the containment continuity for £0.32 each, a very small fraction of the installation cost. Indeed, if done correctly, this creates a high integrity CPC everywhere which would take wholesale demolition to interrupt. This kind of value enhancement I like.

 

[Engineer54]

The company i did my apprenticeship with had 5 production plants as well as other site facilities, including it's own power station, on the one extensive site. All were predominantly wired via metal containment systems. During the yearly 3 week shut downs, sections of each plant's metal containment systems were subjected to what was known then, as Claire testing. I can't honestly recall any significant deterioration being detected during those inspections, ...Oh and None had additional CPC's run in them. The only time we did find weak continuity spots were across building expansion joints, where conduit or trunking crossed using expansion fittings. The containment system was then reinforced at these points for continued use.

I'll not argue the point any further, as stated never used a separate CPC in any metal containment system and don't plan too either!! As far as i'm concerned, when a metal containment system has been professionally erected by skilled tradesmen, it's totally unnecessary electrically, time wise, and cost wise, to fill those containment systems with CPC's. Totally daft too!! lol!!

 

[sparks1234]

I'm not missing the point at all, metal containment systems do NOT require/need separate CPC's.
As i've indicated previously, if a metal containment system has been skillfully erected, using the proprietary conductive sealing paste to all screwed connections and the proprietary zinc paint to any exposed thread on a system suitable for the environment it is installed within, severe deterioration should not be a problem

Totally agree with that

Allowance for future additions and alterations, is not afforded to individual circuit conduit runs, that is normally afforded to DB's and the like. Start going down those lines and the installation is going to get very expensive very quickly. With trunking, you have in most instances, an inherent means of easily accommodating additions and alterations. Just wondering how you allow for incompetent persons undertaking any such work in the future

Most sites that sparks go to in the private sector don't have an unlimited budget and invariably additional circuits are required either when the client moves in or maybe a new tenant takes over the space, so a certain amount of additional capacity is always good. Invariable, most times sparks are asked to install additional circuits it would seem to be a case of "oh, one extra circuit won't hurt", obviously this can have a cumulative effect. It would be lovely to start again but economics generally don't allow such a luxury.

Further, i personally i haven't used solid core single cables in conduit, they are just not suitable or fit for purpose, being pulled into tube as far as i'm concerned, even less so when additional cables are pulled into an existing conduit system, stranded cables are by far, more accommodating all round!! I don't allow inspection bends and Tee's either, those bloody things rip cable insulation to shreds!!




Yes, some metallic conduit systems have been erected in unsuitable environmental conditions, and may well prematurely deteriorate. But then surely that installation would need to be replaced rather than try to fluff around with it, while still deteriorating further??

Probably time to wrap this one up, the only other think I may add is that in areas such as warehouses there are various trunking systems installed, these can be vulnerable to various abuse by forklifts and the like, yes you could put them high but then when changing tenant this is not a consideration that the trunking system is not right for that environment , its just a trunking system to them and does the job. Invariable the trunking can be damaged (which I have seem many a time) and often just left. If you have that earth in place generally that will hold up if the trunking is damaged
Anyway, enough said

 

[Lucien Nunes]

Indeed. It sounds like E54 gets to work on better-maintained systems that the likes of us and does not have to contend with the same levels of damage and neglect. He is designing to suit his local conditions and we to suit ours. I had hoped to hear a few more opinions on the subject but I think we've scared people off!