High integrity earthing

[Spark123]

What's wrong with a 1.5mm² cpc in a 2.5mm² multicore cable?

 

[NotHimAgain]

What's wrong with a 1.5mm² cpc in a 2.5mm² multicore cable?

IMO nothing at all.

 

[tim west]

If you remove one of the live wires from the breaker in the CU to the first socket in relation to which wire is removed then you end up with the sockets all still being live, so how can that be if as you say i've already removed the ONLY live in the circuit??

 

[ColJack]

you still don't get it do you..

the "high integrity" is refering only to the fact that there will always be at least one path to earth from any given earthing point..

that is done either by
1. a cable of adequate size that it won't be easily broken by incidental damage
2. a cable of adequate size that is protected from incidental damage
3. 2 paths from each earthing point such that one path is still available should one path be broken through damage or failure of a mechanical termination.

it's this third one that makes radials comply if the earth at the final point is
a. connected back to the board
b. connected to the earthed metalic path of the conduit / armour feeding it
c. connected to the earth path of another local radial circuit.

this is already the case with ring mains since, as long as each cpc at each point is terminated independantly then failure of any conductor or mechanical termination still leaves every earth point on the ring connected to earth..

 

[NotHimAgain]

you still don't get it do you..

the "high integrity" is refering only to the fact that there will always be at least one path to earth from any given earthing point..

that is done either by
1. a cable of adequate size that it won't be easily broken by incidental damage
2. a cable of adequate size that is protected from incidental damage
3. 2 paths from each earthing point such that one path is still available should one path be broken through damage or failure of a mechanical termination.

it's this third one that makes radials comply if the earth at the final point is
a. connected back to the board
b. connected to the earthed metalic path of the conduit / armour feeding it
c. connected to the earth path of another local radial circuit.

this is already the case with ring mains since, as long as each cpc at each point is terminated independantly then failure of any conductor or mechanical termination still leaves every earth point on the ring connected to earth..

This is a good summary. We might go further and include a description of the problem and the basic principles of the solutions. Note that many prefer the 'two path' solution over the 'more robust path' one.

I will not say more at this stage - the comments made indicate that most understand it all anyway, and you BAS seem to think that you are in no need of guidance.

[/i]

 

[RF Lighting]

Thats remarkably similar to what I wrote all the way back on Page 2

 

[securespark]

No, yours was completely different.

Yours was missing the insulting, "You still don't get it, do you?" remark.

 

[Trazor]

Sorry, I thought this was the "electricians tedious bickering" thread....

Just shows how right you can be..................

 

[ban-all-sheds]

Maybe but does it need to be increased anymore?

The regs say it does.

Surely if you needed 2 ring CPCs for a High integrity earthing RFC then why wouldn't you need the same for a radial circuit?

Because a radial does not start out with the same level of integrity in the first place.

A radial has a radial cpc, a ring has a ring.

Both are deemed to require a higher level of cpc integrity than the normal configuration.

So the normal radial circuit has its normal-integrity radial cpc increased to a high-integrity ring. It now has, crudely, twice the level of integrity.

So a normal ring circuit has its normal-integrity ring cpc increased to two individual ring cpcs. It now has, crudely, twice the level of integrity.

The guidance note will not ensure compliance with BS7671 as it only covers earthing and bonding, none of the guidance notes cover the full scope of BS7671. Differing locations may also require different regulations to be met. It does however generally aid in explaining the aim of a number of the regs regarding earthing and bonding.

Well - that's one way of looking at it, and it could be so, but it does seem a bit of a stretch to interpret "This Guidance Note does not ensure compliance with BS7671" to mean "...because it only deals with a subset of BS7671" rather than "...because it is only guidance and not the official version of BS7671".

 

[ban-all-sheds]

17th - not word for word but might help

543.7.1.3

The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment , such that the total CPC current is likely to exceeed 10mA, shall have a high integrity protective connection complying with one or more of the following:-

(i) A single protective conductor having a cross-sectional area of not less than 10mm squared complying with the requirements of regulations 543.2 and 543.3

(ii) A single CPC of not less than 4mm squared complying with 543.2 and 543.3, the CPC being mechanically protected, eg; within conduit

(iii) Two individual CPC's each complying with section 543. The two CPC's may be of different types eg; metallic conduit together with a cable CPC. One of the CPC's may be formed by metallic sheath , armour or wire braid within the cable.

So basically the same wording as now.

543.7.1.4 Where two CPC's are used the ends shall be terminated independently of each other................

But with an interesting change?

Or clarification? If they wanted to change from what's currently required wouldn't they be more likely to change what the words currently say?

To mention doing something specific with 2 cpcs must mean that 2 cpcs is not the norm for a ring. If it were what is meant by "Two individual CPCs" then it would have been much simpler, and would have been utterly clear, if they had written "For a ring final circuit complying with 433.1.4 & 543.2.9 the ends of the cpc shall be terminated independently of each other"

It's more indication that "two individual cpcs" means "two individual cpcs where normally there is one" and not "the usual single cpc with its ends terminated independently".

 

[ban-all-sheds]

BAS why do you keep saying that is what the regulation say - that is what you say that they say.

When I read my copy, I see the words in black print on a white page "two individual protective conductors".

It really does say that, I'm not just saying it says it.

If you have two individual somethings you must be able to take one of the individual somethings away and be left with one individual something. It's the most basic example of arithmetic that is taught to children very early in life - "two take away one leaves one".

For as long as you fail to realise that not answering the question proves to everybody that you know you are wrong I shall take every opportunity to remind everybody else that you know you are wrong, so again I will ask you this:

If you believe that the drawing posted by Spark123 shows two individual cpcs then please show us how you can remove one of the two individual cpcs to leave one remaining individual cpc.

In any event my first post on this topic indicated that changes in the text may lead to confusion.

Lets flag up some of the errors in their text for you .

The problem starts with 607-02-04. It begins - The wiring of every final circuit and distribution circuit .... Thus including all final circuits.

Earlier versions specifically offered the standard ring main with appropriate modification as an ALTERNATIVE to 607-02-04.

But earlier versions don't matter. Things change. Versions are replaced with later ones. That's why we are now working to the 16th/17th, and not the 1st.

However, all is not lost because I can make 607-02-04 (iii) para 2 fit, even if you can't.

Fit what? One individual cpc as is the norm on a non-high-protective-conductor-current ring final?

This error is followed by the removal from 607-03-01 of the specific indication of permitted protective conductor size (1.5 mm²).

Interesting how you regard changes to the regulations which damage your argument as "errors".

607-03-01 (i) makes clear that spurs must have a high integrity protective
conductor connection complying with 607-02 but it does not make clear the status of the conductors forming the ring. Note that the talk is of a protective conductor connection - it is not just about the protective conductor.

Au contraire - it makes the status of the conductors forming the ring cpc abundantly clear, because it clearly says it must comply with 607-02. And 607-02 clearly says that you must have one or more of:

(i) A single cpc of not less than 10mm²

(ii) A single cpc of not less than 4mm² if it has additional protection

(iii) Two individual cpcs.

607-03-01 says that a ring final circuit has to have a ring protective conductor. So taken together with 607-02, the regulations require one or more of:

(i) A single ring protective conductor of not less than 10mm²

(ii) A single ring protective conductor of not less than 4mm² if it has additional protection

(iii) Two individual ring protective conductors.

Now if you had argued that 1.5mm² could not be used and that 2.5mm² is required I could probably have agreed with you

Now 602 - take a close look at 607-02-04 (iii) paragraph 2 - ring circuit (4 * 2.5) + (2 * 1.5) = ?

However, I am at the CCU and I have two 2.5mm² conductor ends in the mcb terminal (or perhaps terminus) - so that is 2 * 2.5 = 5.

Next I go to the neutral connection bar and I remove the 2, 2.5mm² conductors related to my circuit. 2 * 2.5 = 5

Then I go to the earth connection bar and - you guessed it - I remove the 2, 1.5mm² related to my circuit. 2 * 1.5 = 3

Now I wonder what (2 * 2.5) + (2 * 2.5) + (2 * 1.5) equals - do you know?

but your take on this is frankly ridiculous - your interpretation of what is required does not make engineering sense and you would know that if you actually understood the problem.

The fact that I read what the regulations say rather than what they don't say does not mean that I don't understand the problem.

Does what the regulations say make engineering sense? Kind of - they are saying that if your cpc is of above-average importance you need to beef it up in one or more of the following ways:

Make it bigger.

Increase the redundancy.

A radial has less redundancy than a ring - if a cp conductor falls out of a socket then part of the circuit is hosed, cpc-wise, so 607-03-01 (ii)(a) says "make it a ring", 607-03-01 (ii)(b) says "add a 2nd one" and 607-03-01 (ii)(c) says "join the ends of two radial cpcs to create a ring".

In each case the remedy increases the resilience, or integrity, of the cpc - no longer will part of the circuit be hosed, cpc-wise, if a cp conductor falls out of a socket. It ties in, from the point of view of engineering sense with the fact that if you break the ring on an augmented radial circuit, or lose one of your two cpcs you are back to the normal ratio of cpc Iz:circuit In.

Rings already have that redundancy - one of the arguments always made in their favour is precisely that, that you can have a protective conductor drop out of a socket and not end up hosed, cpc-wise, because there is still a path for cpc currents, albeit only in one direction along one segment of what had been a ring providing two paths.

Normally that's considered acceptable, and normally a worsening of the cpc Iz:circuit In ratio is considered acceptable but here we are dealing with high protective conductor currents, so we have to do something to mitigate the worsening of cpc Iz:circuit In caused by a break in the ring.

607-02-04 says that we can do that

either by making the cpc bigger, i.e. making the cpc Iz:circuit In ratio better than what is normally required so that if cpc Iz drops through the breaking of the ring, cpc Iz:circuit In is still OK

or by providing two ring cpcs instead of one, thus making the aggregate cpc Iz:circuit In ratio better than what is normally required so that if in this case one cpc Iz drops through the breaking of the ring the other cpc is still intact and the aggregate cpc Iz:circuit In is still OK

Is what the regulations say an engineering necessity? I don't know, but I do know that if not then it wouldn't be the only part of the regulations that was flawed in that way.

 

[ban-all-sheds]

If you remove one of the live wires from the breaker in the CU to the first socket in relation to which wire is removed then you end up with the sockets all still being live, so how can that be if as you say i've already removed the ONLY live in the circuit??

FGS - don't be obtuse.

The conductor is of finite length, therefore it has two ends, and both are there at the CU. If you disconnect one end from the breaker the other end is still connected, therefore the conductor is still live.

 

[ban-all-sheds]

you still don't get it do you..

You still don't get it, do you..

this is already the case with ring mains since, as long as each cpc at each point is terminated independantly then failure of any conductor or mechanical termination still leaves every earth point on the ring connected to earth..

OK - so if 607-02-04 (i) means "the normal ring arrangement of a single cpc is OK provided it is a cable of adequate size that it won't be easily broken by incidental damage"

and 607-02-04 (ii) means "the normal ring arrangement of a single cpc is OK provided it is a cable of adequate size that is protected from incidental damage".

What does "two individual protective conductors" mean, because it sure as hell does not mean "one individual protective conductor with each point terminated independently", at least not in any version of English that any rational person would recognise.

 

[ban-all-sheds]

This is a good summary. We might go further and include a description of the problem and the basic principles of the solutions. Note that many prefer the 'two path' solution over the 'more robust path' one.

"Two individual protective conductors". If you think your version provides two individual protective conductors then please show us how you could remove one individual protective conductor and leave the other individual protective conductor remaining.

I will not say more at this stage - the comments made indicate that most understand it all anyway, and you BAS seem to think that you are in no need of guidance.

"Two individual protective conductors". If you think your version provides two individual protective conductors then please show us how you could remove one individual protective conductor and leave the other individual protective conductor remaining.

 

[NotHimAgain]

This is a good summary. We might go further and include a description of the problem and the basic principles of the solutions. Note that many prefer the 'two path' solution over the 'more robust path' one.

"Two individual protective conductors". If you think your version provides two individual protective conductors then please show us how you could remove one individual protective conductor and leave the other individual protective conductor remaining.

I will not say more at this stage - the comments made indicate that most understand it all anyway, and you BAS seem to think that you are in no need of guidance.

"Two individual protective conductors". If you think your version provides two individual protective conductors then please show us how you could remove one individual protective conductor and leave the other individual protective conductor remaining.

As ever BAS you completely miss the point - I don't care about your way of defining two individual protective conductors. I tried to give you a clue earlier when I pointed out that we are concerned with high integrity protective conductor CONNECTIONS.

As ever BAS you are so bent on proving you are right that you fail to see the true problem and its solutions. You are so convinced that you somehow know more about this subject than all of the engineers that have considered it and, than all of the posters on this site.

I just hope that no one reading this actually needs proper guidance on this because it is a serious safety issue.