I think I explained the customer is not concerned about cost of wasted power against extra material costs.
The differential cost between a few hundred metres of 2.5mm or 4mm is trivial compared to the budgets on the renovation.
Maximum cable size
- Thread starter bernardgreen
- Start date
I think I explained the customer is not concerned about cost of wasted power against extra material costs.
The differential cost between a few hundred metres of 2.5mm or 4mm is trivial compared to the budgets on the renovation.
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given todays prices of t+e mean theres about £40 difference per 100m.
I would estimate that the customer is going to put his costs up by £80 to £120. That makes no allowance for any other additional cost such as, using deeper boxes and greater labour cost to install the 4mm cable.
At the start of this thread, you told pjcomp that the customer wanted to save on the cost of lost energy due to dissipation. There was no mention of any safety issues at that point.
What do think is a reasonable figure to assume for the average loading of a RFC over its life span? Personally, i don't know. I would guess a real figure is a lot closer to 6A than 30A.
How does that affect the customers 'cost of lost energy' calculation?
I would estimate that the customer is going to put his costs up by £80 to £120. That makes no allowance for any other additional cost such as, using deeper boxes and greater labour cost to install the 4mm cable.
At the start of this thread, you told pjcomp that the customer wanted to save on the cost of lost energy due to dissipation. There was no mention of any safety issues at that point.
What do think is a reasonable figure to assume for the average loading of a RFC over its life span? Personally, i don't know. I would guess a real figure is a lot closer to 6A than 30A.
How does that affect the customers 'cost of lost energy' calculation?
I said:
which could imply concern about cost of wasted power. But I know the customer and his main and over riding priority is a system with the best efficiency and minimum hazards. To a standard higher than BS 7671 in fact.
Which means "electricians" who work rigidly to the rules ( such as declaring oversized cable "illegal" ) will not be able to apply common sense and design an installation that is better than the compromise permitted under BS7671
And to clarify why he accepted my advice about using rings. Install as a radial and then with a single fault it is possible for the sockets at the end to be deprived of an effective CPC. True ? Live and neutral but no earth. It will be found at install if tested but if the fault develops later there is a hazard that can only be found by shock, hopefully not fatal, or regular testing.
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We've been down the 'rings are tolerant to a single fault' road before.
I'm not sure i agree with that anyway, but, they are certainly not tolerant to multiple faults. So, if one joint can work loose/overheat, why can't several?
This would render the faulty RFC just as hazardous as a faulty radial circuit.
I think we will just have to agree to disagree on that as i feel that under general circumstances it is an empty argument, given that there should be periodic testing and inspection carried out.
A circuit which has been installed correctly by a competent person should not have failed terminals after just a few years.
If the customer does indeed have a thorough knowledge of electricity and regulations, then surely he is aware of this?
IMO, the arguement of what the electrician actually said is a non-starter as you were not privvy to that conversation and have only received the information second-hand.
I would be reluctant to publicly slate the (possible) good name of the electrician based on what is nothing more than hearsay.
I'm not sure i agree with that anyway, but, they are certainly not tolerant to multiple faults. So, if one joint can work loose/overheat, why can't several?
This would render the faulty RFC just as hazardous as a faulty radial circuit.
I think we will just have to agree to disagree on that as i feel that under general circumstances it is an empty argument, given that there should be periodic testing and inspection carried out.
A circuit which has been installed correctly by a competent person should not have failed terminals after just a few years.
If the customer does indeed have a thorough knowledge of electricity and regulations, then surely he is aware of this?
IMO, the arguement of what the electrician actually said is a non-starter as you were not privvy to that conversation and have only received the information second-hand.
I would be reluctant to publicly slate the (possible) good name of the electrician based on what is nothing more than hearsay.
Bernard, I'm having trouble understanding how using a 4mm Ring Final Circuit as opposed to a 2.5mm RFC or 4mm Radial circuit is either more efficient or less hazardous - if both circuits are protected by the same 32Amp MCB and a 30mA RCD?
Can you help me out here?
I have fitted both 2.5mm RFC and 4mm radials - but apart from issues with voltage drops - which doesn't appear to be the issue here - I would never use 4mm on a RFC - since the installation costs to the customer would be double that of a normal 2.5mm RFC.
Mikehail
The comments from the "electrician" were written down by him, so no escape using the "only hear say" route.
Some years ago I found a radial where the CPC had corroded away in a back box leaving some sockets without effective earthing.
But as you say this disccusion will go on for ever.
Riveralt
The voltage drops were on the design limit for 2.5mm due to distance between CU and areas served.
Cost of materials of secondary importance.
The comments from the "electrician" were written down by him, so no escape using the "only hear say" route.
Some years ago I found a radial where the CPC had corroded away in a back box leaving some sockets without effective earthing.
But as you say this disccusion will go on for ever.
Riveralt
The voltage drops were on the design limit for 2.5mm due to distance between CU and areas served.
Cost of materials of secondary importance.
Hi Bernard,
Fair enough, if the 'electrical operative'
has committed his comments to paper, then he is a bit of a clown.
Why don't you post his comments in full, so we can all have a chuckle.
From another recent thread, i understand that you prefer RFCs of one form or another for one reason or another when compared with radial circuits. Fair enough, no probs - thats your choice. I take a different view to you on the subject, but hey- theres more than one way to skin a cat.
Personally, i think that if a circuit goes so many years un-checked that it has corroded away, then no matter how many conductors you supply to any given terminal, the circuit will, at some point become dangerous to use. I think that if there were two cpc conductors within the same backbox, they would probably have corroded at approximately the same rate and failed together, but thats only my guess
I suppose both of these thoughts could be true:-
I saw a corroded terminal, so from now on, each of my terminations shall be part of a RFC to ensure safety.
and
I saw a corroded terminal, so from now on, i shall advise my customers of the importance of periodic inspection and testing to ensure safety.
Fair enough, if the 'electrical operative'
has committed his comments to paper, then he is a bit of a clown.Why don't you post his comments in full, so we can all have a chuckle.
From another recent thread, i understand that you prefer RFCs of one form or another for one reason or another when compared with radial circuits. Fair enough, no probs - thats your choice. I take a different view to you on the subject, but hey- theres more than one way to skin a cat.
Personally, i think that if a circuit goes so many years un-checked that it has corroded away, then no matter how many conductors you supply to any given terminal, the circuit will, at some point become dangerous to use. I think that if there were two cpc conductors within the same backbox, they would probably have corroded at approximately the same rate and failed together, but thats only my guess
I suppose both of these thoughts could be true:-
I saw a corroded terminal, so from now on, each of my terminations shall be part of a RFC to ensure safety.
and
I saw a corroded terminal, so from now on, i shall advise my customers of the importance of periodic inspection and testing to ensure safety.
Bernard,
You've done the calcs for 2.5 and these are okay, albeit near the limit..
You don't like radials, so you tell him he needs a 4mm RFC.
If you are so adamant he needs this, why haven't you done the install?
You've done the calcs for 2.5 and these are okay, albeit near the limit..
You don't like radials, so you tell him he needs a 4mm RFC.
If you are so adamant he needs this, why haven't you done the install?
The first "electrician" did the calcs on 2.5mm
I do not dislike radials. I prefer RFCs for the reasons I mentioned elsewhere.
I was not adamant, it was his decision based on my advice. He is about 200 miles away and the install will be in 3 possibly 4 phases ( phases in time ) over several weeks to fit in with other work so requires a local electrician.
I'm not certain its been established that the values were on the limit. A value of 2% volt drop has been mentioned in this thread somewhere. I did ask Bernard whether the customer knew what the actual limit for volt drop was for this type of circuit, but I don't recall reading about a response from the customer
To mikhailfaradayski
The original point was that an "electrician" could not understand that using a cable size larger than the calculations called for was permitted and advantaguous to the client.
You can divert the conversations from that as much as you like by questioning every little detail mentioned but that will not change the fact that the "electrician" was a book of rules person un-able to apply a combination of common sense and basic electrical theory to the situation.
The original point was that an "electrician" could not understand that using a cable size larger than the calculations called for was permitted and advantaguous to the client.
You can divert the conversations from that as much as you like by questioning every little detail mentioned but that will not change the fact that the "electrician" was a book of rules person un-able to apply a combination of common sense and basic electrical theory to the situation.
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.
Hi Bernard,
I don't think I'm attempting to divert the conversation, rather trying to understand how any practicing electrician would make such a statement, its the first time I've ever heard that said and just seems a little bizarre to me. I was rather questioning the possibility of the customer perhaps getting his side of the story a little bit wrong, then subsequently calling the guys competence into question. Further to that, I was in some way trying to verify just how much the customer really does know himself. Its still a little unclear to me
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