Maximum cable size

[scousespark]

This thread seems a tad confusing.

The first electrician turns up and calculates a 2.5mm RFC is fine. The client says "I want it in 4mm" as his dad's mate, who is an electrician, has told him this is what he needs. He also has an excellent grasp of electrical theory and agrees that only a 4mm RFC is the safe option.
Apparently a 2.5 mm RFC is NOT safe, as the volt drop is NEAR the limit.
Radials are not the answer, as they have an apparent design flaw, where a loose connection can cause a fire.

Any loose connection can cause a fire. However, I don't see vast swathes of england burning. Maybe, proper installation stops this

The electrician puts in writing that he can't do it, as it breaks the regs.
Why did he do that.

I would think the real scenario is that the electricain has tried to dissuade the client and this is where the confusion has arisen.

 

[scousespark]

There are plenty of commercial ring finals wired in 4mm²

And some of them have automatic detection of a failed or failing connection to alert that a repair is needed. Often the repair happens before there any loss of power to any of the sockets.

Cannot do that on a radial.

Just how many such ircuits have you installed in a domestic property Bernard. Seems like a bit of overkill.

 

[bernardgreen]

Why is it that some electricians feel they can dictate to the client what the client needs ? If go to buy food I do not expect the shop to tell me what I can and cannot have from the food available in the shop or to tell me what my next week's menu must be. They can advise but not dictate, and of course they cannot sell me poisonuous or dangerous food.

I haven't installed automatic single fault detection on any domestic RFC but I have seen it specified on at least two commercial installations where ring circuits were used because of their single fault tolerance.

Apparently a 2.5 mm RFC is NOT safe, as the volt drop is NEAR the limit.

That was never said. The volt drop could be well below the limit on a short length of cable when the CURRENT was far beyond the safe limit for the cable.

 

[mikhailfaradayski]

This thread seems a tad confusing.

I agree

The first electrician turns up and calculates a 2.5mm RFC is fine. The client says "I want it in 4mm" as his dad's mate, who

may or may not be

an electrician

who may or may not be aware of current regulations

, has told him this is what he needs. He also has an excellent grasp of electrical theory and agrees that only a 4mm RFC is the safe option.

after being persuaded so, un-necessarily

Apparently a 2.5 mm RFC is NOT safe, as the volt drop is NEAR the limit.

apparently, but the customer doesn't appear to know what that limit is?? From a description of the house being just 40ft (ish) from front to back, i am a little surprised that the calculations show that VD is near its limit for this type of circuit

Radials are not the answer, as they have an apparent design flaw, where a loose connection can cause a fire.

Any loose connection can cause a fire. However, I don't see vast swathes of england burning. Maybe, proper installation stops this

indeed! Couple that with appropriate inspection and testing, as guidance suggests.

We have been told that...

The electrician puts in writing that he can't do it, as it breaks the regs.
Why did he do that.

This is confusing me aswell, I would love to see a scan of that letter myself to remove the possibility of chinese whispers and a bit of 'he said she said' malarky

I would think the real scenario is that the electricain has tried to dissuade the client and this is where the confusion has arisen.

That probably sits close to the heart of the matter....

 

[Risteard]

At first we are told that a ring final circuit (not "final ring circuit" whatever that is) wired in 4mm^2 cable is necessary as voltage drop is close to the limit. Later on we are told that at full load (26A or what has been used for design current?) it has been calculated at close to 2%.

2% is not borderline for the permitted 5%. In fact it is nowhere near it. Which again raises the question of why the ring final circuit needs conductors with a greater csa.

 

[ban-all-sheds]

Whether "required" or "desired" is irrelevant, the fact is that's what the tw** pretending to be an electrician was asked to install.

This topic is not about how the request arose, it is about the tw** pretending to be an electrician claiming that a 4mm² cable was not allowed if a 2.5mm² one would have complied with the Wiring Regulations.

 

[scousespark]

Actually BAS, there is no actual evidence as to what happened between the client and the electrician.

All we know is that Bernard gave advice that the house needed a non-standard RFC (in that the normal 2.5mm cable is too small). His mate has an excellent understanding of electrical theory, so he agreed.

The electrician gave some reply to the request to install a 4mm RFC, saying he wouldn't/couldn't do so and then wrote it down for confirmation.

Bernard and yourself have decided he's not up to the job. At least Bernard has spoken to he client. You've convicted him on Bernard's say-so.

 

[ban-all-sheds]

Actually BAS, there is no actual evidence as to what happened between the client and the electrician.

The comments from the "electrician" were written down by him, so no escape using the "only hear say" route.

At least Bernard has spoken to he client. You've convicted him on Bernard's say-so.

I'm working on the basis that all of this information is correct:

The electrician is stating that as long as the voltage drop at full load is less than 2% the system is correct and any changes will make it not correct.

The electrician has calculated the voltage drop as being just less than 2% so insists 2.5mm is the correct and only cable to use.

the electrician said that 4mm was not permitted under the rules for a ring final.
.
.
The "electrician" took this to mean he HAD to use 2.5mm and that to use 4mm would be "illegal".

The "electrician" said 4mm would contravene the regulations so he could not use it.

particularly given the explicit confirmations here: //www.diynot.com/forums/viewtopic.php?p=1877062#1877062

Do you want to suggest that bernard is not telling the truth?

 

[mikhailfaradayski]

Do you want to suggest that bernard is not telling the truth?

I doubt that Bernard is deliberately saying something which is untrue, but It seems that Bernard may not have spoken directly to the electrician. Rather that he has received the information second hand from the customer or the customer's dad.

I would still like to see the words as (reportedly) written by the accused before concluding that he is a Tw**. I'm not judge and jury in a kangaroo court.

I still find it a bit difficult to swallow the story that someone who has the knowledge and ability to calculate VD for a RFC (suggesting that he could well know what he is talking about) would then go on to talk about the legality (not the appropriateness or costs ) of oversizing a cable.

If the letter was scanned and posted here, it may well clear up the confusion.

 

[mikhailfaradayski]

Just another thought.

I wonder if the accused electrician possesses CG2391 or similar?
Was/Is he registered with a competent person scheme?

 

[scousespark]

Actually BAS, there is no actual evidence as to what happened between the client and the electrician.

The comments from the "electrician" were written down by him, so no escape using the "only hear say" route.

At least Bernard has spoken to he client. You've convicted him on Bernard's say-so.

I'm working on the basis that all of this information is correct:

The electrician is stating that as long as the voltage drop at full load is less than 2% the system is correct and any changes will make it not correct.

The electrician has calculated the voltage drop as being just less than 2% so insists 2.5mm is the correct and only cable to use.

the electrician said that 4mm was not permitted under the rules for a ring final.
.
.
The "electrician" took this to mean he HAD to use 2.5mm and that to use 4mm would be "illegal".

The "electrician" said 4mm would contravene the regulations so he could not use it.

particularly given the explicit confirmations here: //www.diynot.com/forums/viewtopic.php?p=1877062#1877062

Do you want to suggest that bernard is not telling the truth?

I'm not sayng Bernard is not telling the truth. However, he was 200 miles away when this conversation took place.

 

[scousespark]

Why is it that some electricians feel they can dictate to the client what the client needs ? If go to buy food I do not expect the shop to tell me what I can and cannot have from the food available in the shop or to tell me what my next week's menu must be. They can advise but not dictate, and of course they cannot sell me poisonuous or dangerous food.

I haven't installed automatic single fault detection on any domestic RFC but I have seen it specified on at least two commercial installations where ring circuits were used because of their single fault tolerance.

Apparently a 2.5 mm RFC is NOT safe, as the volt drop is NEAR the limit.

That was never said. The volt drop could be well below the limit on a short length of cable when the CURRENT was far beyond the safe limit for the cable.

I'm not dictating the design and your analogy is nonsense. You have given your advice, the electrician challenged it so he is not up to the job. This despite you being 200 miles away and basing your design on phone conversations.

Your OP stated you had determined the bigger cable was required because of volt drop.

 

[ban-all-sheds]

Bernard's design is irrelevant, no matter what you think of it, because even if it's the daftest design ever that does not alter the fact that the electrician who was asked to install it said that the Wiring Regulations did not permit the use of 4mm² for a ring final, and said that as 2.5mm² would be compliant, changing to a larger size would make it non-compliant.

Whether Bernard's analogy is the biggest load of nonsense ever is irrelevant, because that does not alter the fact that the electrician who was asked to install it said that the Wiring Regulations did not permit the use of 4mm² for a ring final, and said that as 2.5mm² would be compliant, changing to a larger size would make it non-compliant.

Whether Bernard's voltage drop calculations are spot on or laughably wrong is irrelevant, because that does not alter the fact that the electrician who was asked to install it said that the Wiring Regulations did not permit the use of 4mm² for a ring final, and said that as 2.5mm² would be compliant, changing to a larger size would make it non-compliant.

 

[scousespark]

Bernard's design is irrelevant, no matter what you think of it, because even if it's the daftest design ever that does not alter the fact that the electrician who was asked to install it said that the Wiring Regulations did not permit the use of 4mm² for a ring final, and said that as 2.5mm² would be compliant, changing to a larger size would make it non-compliant.

Whether Bernard's analogy is the biggest load of nonsense ever is irrelevant, because that does not alter the fact that the electrician who was asked to install it said that the Wiring Regulations did not permit the use of 4mm² for a ring final, and said that as 2.5mm² would be compliant, changing to a larger size would make it non-compliant.

Whether Bernard's voltage drop calculations are spot on or laughably wrong is irrelevant, because that does not alter the fact that the electrician who was asked to install it said that the Wiring Regulations did not permit the use of 4mm² for a ring final, and said that as 2.5mm² would be compliant, changing to a larger size would make it non-compliant.

With respect, the electrician was given a design spec based solely on Bernard's calculations. He has only been able to quote his mate's son, with reference to some alleged document the electricain has written. regardless of his skill, why would he do that?

Unless you happen to have been within earshot of the conversation this is heresay.

 

[ban-all-sheds]

With respect, the electrician was given a design spec based solely on Bernard's calculations.

FGS - that is completely irrelevant - why do you keep on trying to cloud the issue?

He has only been able to quote his mate's son, with reference to some alleged document the electricain has written. regardless of his skill, why would he do that?

Why would who do what regardless of his skill? Why would the "electrician" write what he has reportedly written, regardless of his skill? Maybe he has no skill.

Unless you happen to have been within earshot of the conversation this is heresay.

1) Bernard assures us it is not because there is written evidence.

2) Even if you don't want to believe a word Bernard says will you stop trying to make out that things like the design, the wisdom of trying to do a design over the phone, the validity of the voltage drop calculations and so on have any relevance.

It is quite clear that you don't want to believe Bernard and that therefore you are engaging in ad hominem criticisms in an attempt to discredit what he says.

What he says is quite simple - however arrived at, the "electrician" was asked to use 4mm² cable for a ring final, and reportedly refused to do so for all the wanky and ludicrously ignorant reasons given above.

If you don't believe that, then say so and leave it at that, but stop trying to cast doubt on Bernard's report by finding things wrong with his design.