High integrity earthing

[2scoops0406]

7 pages, quite impressive Sorry, 8 now

 

[tim west]

My argument was because of that particular diagram and the assumption by yourself that that was how a RFC is wired.
All the electricians that I have ever worked with and myself know that a RFC consists of two T&E cables or 2 of each LNE singles leaving the CU and forming a loop that serves all the socket outlets within that RFC.

 

[NotHimAgain]

BAS Wrote:

I don't know. Maybe because they are inarticulate fools?

Are you saying that they know that their text is imprecise, but they use it anyway, or are they just unwitting victims of their lack of proficiency with the English language?

As to the rest of your last post - I think you have lost me - but then I am just an engineer BAS you will have to make allowances.

Now, just in case anyone viewing these post is actually remotely interested in understanding the problems present by circuits with high protective conductor currents - a brief review:

Introduction
Some circuits operate with relatively high currents flowing in the protective conductor - these may have been deliberately introduced i.e. Functional Earthing, or they may be the result of leakage due to the characteristics of the current using equipment (i.e. we may term this leakage current but not due to a fault)

A typical example of functional earthing - a supply line low pass filter. These filters are used to reduce the effects of noise signals appearing on the supply. They are often associated with telecoms and IT equipment, but any equipment that utilises 'electronic' systems may have them (washing machine, microwave etc.)

A typical example of electrical equipment that may leak current in normal service would be a heating element that encapsulates the heater wire in a powder insulating material, such as a cooker radiant ring.

Next we need to define what we mean by high protective conductor current. We start to be concerned at currents exceeding 3.5mA (many appliances are 'allowed' to create protective currents of this magnitude). A single item of equipment that might produce currents in the range 3.5mA to 10mA must either be permanently connected, or be connected using a socket outlet complying with BS EN 60309-2.

When the current is likely to exceed 10mA from a single item of equipment we have to introduce circuit modifications to restore the level of protection that we normally apply to protection against fault current (indirect contact protection). Similarly, if a number of items of equipment could collectively produce a current exceeding 10mA, once again we introduce circuit modifications.

Now I have not, as yet, given any indication why these pretty small - "high protective conductor currents" - present a hazard.

So what is the hazard, why 10mA, how do the solutions work?

If anyone is interested I will give more detail.

 

[ban-all-sheds]

My argument was because of that particular diagram and the assumption by yourself that that was how a RFC is wired.

When you strip away the points of connection to expose the topology of the ring you can see that that is how a RFC is wired.

All the electricians that I have ever worked with and myself know that a RFC consists of two T&E cables or 2 of each LNE singles leaving the CU and forming a loop that serves all the socket outlets within that RFC.

If you have 2 each of LNE singles then you have 6 conductors.

Each conductor has two ends.

If each conductor leaves the CU and returns in a loop then you must have 12 ends to deal with at the CU.

Please draw me a diagram showing that.

 

[tim west]

Don't know where you think 12 conductors comes into the equation? but 2 lives 2 neutrals and 2 earths does indeed make 6 wires per RFC in the CU and 6 wires accordingly at each socket.

 

[ban-all-sheds]

BAS Wrote:

I don't know. Maybe because they are inarticulate fools?

Are you saying that they know that their text is imprecise, but they use it anyway, or are they just unwitting victims of their lack of proficiency with the English language?

An interesting philosophical question - is a fool only a fool if he realises it?

As to the rest of your last post - I think you have lost me - but then I am just an engineer BAS you will have to make allowances.

Well - I'm sorry I lost you - I didn't realise I'd written anything too complicated for you to understand.

I'll try to make it simpler.

Why was it inconsistent of me to express a belief that terminating the ends of conductors separately is not done to create two current paths and then to express surprise when you implied it is?

I can't though think of a simpler way to ask why when you look at this:

you see "two individual protective conductors"?

But I will try another question, which I hope will be simple enough for you to understand:

Why have you not answered a single one of my questions where I've asked you to draw, identify or count conductors?

 

[daytona]

My argument was because of that particular diagram and the assumption by yourself that that was how a RFC is wired.
All the electricians that I have ever worked with and myself know that a RFC consists of two T&E cables or 2 of each LNE singles leaving the CU and forming a loop that serves all the socket outlets within that RFC.

yes two twin and earth cables leave the CU you are right about that bit.

the notion that therefore 2 conductors form the ring is still wrong.using your theory,if a ring had ten sockets on it ,then that ring would have many more cables than the two you describe.so your still wrong.

you need to get the idea of how it looks on first fix,to how it actually manifests itself when its all up and running.

i dont know how your struggling to see this.

 

[NotHimAgain]

BAS Wrote:

Why have you not answered a single one of my questions where I've asked you to draw, identify or count conductors?

Because they represent a fatuous argument - I did, in fact, answer but you decided that I should carry out continuity tests because this would some how prove your point.

Continuity tests prove nothing - they can be applied to one or many circuits at the same time. If I followed your logic I could no doubt prove that a measurement of Zs proves that the circuit from the supply transformer to the point of test is a single conductor.

Regardless of all of this - in my first post I did point out that some confusion may have resulted because of the text used. What are you trying to prove BAS - you know as well as I do that you have no technical point, no safety case, just semantics.

Whatever argument prevails the world will be as dangerous or safe as it was before - nothing of any significance to electrical safety will have changed.

 

[ban-all-sheds]

Don't know where you think 12 conductors comes into the equation?

I didn't say anything about 12 conductors.

Assuming it is of finite length, a conductor has 2 ends.

Both ends may or may not be connected at the CU. If only one end is connected and the other end is not then we have a radial circuit.

If both ends are connected at the CU, thus forming a loop or a ring, we have a ring circuit.

So for each conductor in the ring we have two ends at the CU. In other words if you take the number of conductors and multiply by two you'll get the number of ends, alternatively if you take the number of ends and divide by two you'll get the number of conductors.

It's a very widely understood paradigm, and if you say that a ring circuit has 2 of each LNE, that's 2 x 3 = 6 conductors x 2 = 12 ends.

However, if you can only find 6 ends, then that's 6 ÷ 2 = 3 conductors, i.e. 1 of each LNE

but 2 lives 2 neutrals and 2 earths does indeed make 6 wires per RFC in the CU

Please draw me a circuit diagram with 6 conductors in a ring, or a loop starting and ending at the CU.

and 6 wires accordingly at each socket.

What if a conductor wasn't cut at a socket, but just had a section of sleeving removed, and then folded double at the bare length and that inserted into a terminal - would that conductor still be 2 wires?

 

[tim west]

I perfectly understand daytona it seems to me its you thats getting confused?
The drawing posted by Bas neither states 1st fix or 2nd fix.

Bas
you actually said 12 ends at the CU so I ask again where do 12 ends come into the equation?

Ask anyone on here how many lives are in the backbox of a socket on a RFC and they should say two, not one but two.

 

[SeanT]

Ask anyone on here how many lives are in the backbox of a socket on a RFC and they should say two, not one but two.

There's three in a few of mine - should I pull the third one out? (might **** the wife off a bit if she's ironing using that socket...)

 

[tim west]

There's three in a few of mine - should I pull the third one out? (might p**s the wife off a bit if she's ironing using that socket...)

I would have thought shed be ****ed off having to do the ironing anyway offer to do it for her

 

[daytona]

TIM
i was just pointing out that to have two cables on a ring,you would only be able to have one socket,and even that wouldnt wash once you connected up and completed that circuit

 

[ban-all-sheds]

BAS Wrote:

Why have you not answered a single one of my questions where I've asked you to draw, identify or count conductors?

Because they represent a fatuous argument - I did, in fact, answer but you decided that I should carry out continuity tests because this would some how prove your point.

The first question I asked you had the drawing of a ring with L/N/E, and I asked you how many cpcs it had. You didn't answer.

Then there were a few questions about continuity tests, and the sorts of readings you'd expect to get if you connected the ends of a ring final conductor to your tester, and what you'd get if you connected to the ends of two separate conductors. You attempted to obfuscate by saying the values weren't relevant, then by introducing the idea that the two radial conductors might be connected, and finally describing how you could go to each socket and count cables - none of which was what I asked.

I then asked you this:

I take a length of twin and earth cable. How many conductors do I have in total?

Through some undefined molecular welding technique I join the ends of the conductors so the cable forms a completely unbroken ring. How many conductors do I have in total?

At an indeterminate number of points on the ring I remove the sheathing and sleeving etc, but I do not cut any of the cores. How many conductors do I have in total?

At one of those points I connect a current source. How many conductors do I have in total?

At the other points I connect current sinks. How many conductors do I have in total?

and you didn't answer.

I then asked you this:

Also I would draw to your attention the last sentence in that paragraph. If the requirement for two individual protective conductors is met by a cable with one protective conductor bent round so that the ends touch, what is the logical explanation for the possible existence of yet another individual protective conductor formed by the protective sheath, armour or wire braid of the cable? Surely it can't mean that the conductor in the cable is one cpc, and the armour etc is the 2nd?

Or if it does mean that, when the cable is formed into a ring, are there then 3 cpcs? Or 4? Or do we then go back to just counting the core as 1, in order to remain in compliance with (iii), which only allows for 2 cpcs?

and you didn't answer.

I then asked you to say, in my diagram of conductors labelled A - H how many conductors were present in each scheme, and you didn't answer. In fact, I asked you twice, and you ignored it twice.

I asked you how, if you took one conductor and bent it round so that the ends touched, you then had two conductors, and you didn't answer.

It seems you think that if you pretend that my questions are in fact fatuous arguments you can ignore them with impunity, whereas the reality is, as you know full well (which is why you won't answer them) you can't give any logical, reasonable or consistent answers which don't show that you also know full well that a ring final cpc is not two individual conductors.

Regardless of all of this - in my first post I did point out that some confusion may have resulted because of the text used. What are you trying to prove BAS

That the version of a "high integrity cpc" favoured by many here does not comply with the regulations as written.

you know as well as I do that you have no technical point, no safety case, just semantics.

Unless, of course, the regulations do mean what they actually say, and the requirement really is for "two individual protective conductors", i.e. this:

(Once cpc shown green, the other yellow, for clarity).




Oh, and BTW - I've also asked you twice why you said it was inconsistent of me to express a belief that terminating the ends of conductors separately is not done to create two current paths and then to express surprise when you implied it is.

And you've refused to explain that accusation too.

 

[ban-all-sheds]

Bas
you actually said 12 ends at the CU so I ask again where do 12 ends come into the equation?

OK - let's try this again.

Here is a live conductor:

Now let's bend it into a loop, or ring, so that both ends are present at the CU.

Now let's similarly add a neutral and an earth.

I can now see 1 live, 1 neutral and 1 earth, leaving the CU, looping around and returning, i.e. 1 of each LNE singles.

All the electricians that I have ever worked with and myself know that a RFC consists of two T&E cables or 2 of each LNE singles leaving the CU and forming a loop that serves all the socket outlets within that RFC.

So let's add some more so that we have 2 of each.

And now let's count the ends.