House Re-Wire Plan please critique

[holmslaw]

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[riveralt]

But Radials are much more in voge, using 4mm T&E, usually comes in cheaper on materials too.

This is wrong and since the OP seems to be a cost conscious person inappropriate. The price of 100m of 4mm T&E cable at TLC is £93.60 while 100m of 2.5mm T&E is £55.20. Remember that historically the total floor area served by RFC is 100m^2 while for radials it is 75m^2 So given that his initial outline plan is for three RFC it is possible that he may need three or more radial circuits.

Well if we look that in liner metres, if you say for an easy example where running a circuit that was 10M in total length.
RFC in 2.5T&[email protected] PM x10x2 equals in total £11.04
Radial in 4.00T&[email protected] PM x 10 equals in total £9.36
and cheaper even still for an A3 circuit.

Absolutely correct .... if you were a poor designer... Why would you bother with a linear RFC? Why would you run the cable all the way back to the board in such a situation - you wouldn't - you would set it up as radial circuit. You really are stretching the maths to make your point work here.

As I said each circuit should be designed to meet the needs of the client, the regulatory needs and the price the client is prepared to pay. A well designed 32Amp RFC will always be cheaper than a 32Amp radial circuit.

With copper prices expected to triple over the next few years watch out for the return to vogue of RFC - now if we could just teach people how to test them properly

 

[dingbat]

With copper prices expected to triple over the next few years watch out for the return to vogue of RFC

The ring final circuit has always used more copper than necessary. The original assumptions which brought about its introduction were quite simply incorrect.

 

[riveralt]

With copper prices expected to triple over the next few years watch out for the return to vogue of RFC

The ring final circuit has always used more copper than necessary. The original assumptions which brought about its introduction were quite simply incorrect.

Come on dingbat I thought you were good at maths!

 

[dingbat]

I am.

 

[riveralt]

The ring final circuit has always used more copper than necessary. The original assumptions which brought about its introduction were quite simply incorrect.

I agree there is more copper used than necessary - but not necessarily more copper than the equivalent radial circuit.

I'm using csa mm^2 - 32Amps RFC and 32Amp radial as comparisons - since that was the original discussion point. (I know you could challenge this by saying we could use radial circuit A3 and/or ring circuit A1)

Per metre 4mm (cpc 1.5mm) T&E uses 46% more copper than 2.5mm (T&E). When 4mm has a cpc of 2.5mm it is uses 61% more copper than 2.5mm.
To keep it simple, for a straight forward radial loop in and out circuit of 100 metres the equivalent RFC would need to be more than 141m or 161m (cpc 2,5) before more copper was used.

Now I'm not saying that RFC is better than a radial circuit - each has its own value. However, only in a very badly designed RFC would the amount of copper used be more than a radial circuit.

 

[PrenticeBoyofDerry]

Absolutely correct .... if you were a poor designer... Why would you bother with a linear RFC? Why would you run the cable all the way back to the board in such a situation - you wouldn't - you would set it up as radial circuit. You really are stretching the maths to make your point work here.

I always do stretch the maths!
You make a fair point and my example was shyte.
But as you have already mentioned it is down to design and the needs of the client, in some cases a RFC will be the most logical and the least costly material wise, but there will be occasion when this is not true.
I never said I would not consider using an RFC, I'd be fool if on occasions I didn't.

 

[ban-all-sheds]

IMO they should be last resort, i.e. radials should be the default and only if you just cannot make one work should you go for a ring.

 

[PrenticeBoyofDerry]

You will need to have RCD protection for all circuits, unless they are installed using either by using mechanical protection or cables are buried at least 50mm in to walls.

They need rcd protection regardless of mechanical protection or depth in wall. Exceptions can be made for particular items and these must be clearly identified. 411.3.3

522.6.6
522.6.7
Tells me otherwise.

 

[mattysmithuk]

Wow thanks for all the replies! I will be definatly running a circuit to the fridge and boiler seperate to the rest of the Kitchen supply but I had read somewhere that you put these on a MCB rather than a RCD protected side of the CU are all parts of the CU now protected by RCD? I read that this was done as RCD's were more prone to tripping out than MCB's but from another source i read that the just need to be put on their own RCD or RCBO so that they do not trip out when another item on the circuit protected by the RCD has an issue.

I have a ring in place that is currently serving the whole house the plan is to change this existing ring to only supply upstairs introduce a new ring downstairs in the living room and then a seperate circuit for the kitchen, cooker, outside lights/plug. I will produce a video and upload it to youtube with a walk through of what is planned tomorrow and see what you think I am sure I wil be able to provide a far better explaination of what is planned.

After seeing that link where I can rent the test equipment I am seriously considering doing the training myself. I work in IT at the moment and without wanting to sound like a ass I aint stupid and I'm sure I can pick this up as a additional skill without too much trouble. Im sure as well that once quailified I could pick work up at the weekends from friends and so on that would make it pay for itself over the corse of a year.

Thanks again for all the replies!

 

[riveralt]

After seeing that link where I can rent the test equipment I am seriously considering doing the training myself. I work in IT at the moment and without wanting to sound like a ass I aint stupid and I'm sure I can pick this up as a additional skill without too much trouble. Im sure as well that once quailified I could pick work up at the weekends from friends and so on that would make it pay for itself over the corse of a year.

This sounds like a good course for you:

http://www.tradeskills4u.co.uk/cour...bec2a667a44b&gclid=CPnFrMC_uqYCFQ1O4QodNlWmHw

Do the google there are lots of others of a similar standard

 

[PrenticeBoyofDerry]

Wow thanks for all the replies! I will be definatly running a circuit to the fridge and boiler seperate to the rest of the Kitchen supply but I had read somewhere that you put these on a MCB rather than a RCD protected side of the CU are all parts of the CU now protected by RCD? I read that this was done as RCD's were more prone to tripping out than MCB's but from another source i read that the just need to be put on their own RCD or RCBO so that they do not trip out when another item on the circuit protected by the RCD has an issue.

You do put the fridge and boiler on MCBs you can buy CU's that one side is protected by a RCD and the other is not.
The non protected side can house both MCBs and RCBOs.
This will help nuisance tripping of several circuits at the same time.
But when circuits are protected by MCBs only special requiremets are needed, which we have already covered.

 

[RF Lighting]

This is a house I rewired to the 17th edition.

From the main switch:

(1)Upstairs ring final circuit. (13 points in 3 bedrooms, landing and loft)
(2)Downstairs ring final circuit. (12 points in hall, lounge and kitchen diner)
(3)6.0mm² radial for hob
(4)4.0mm² radial to kitchen gridswitch for washer, dryer, dishwasher.
(5)2.5mm² radial for oven and extractor hood.
(6)2.5mm² radial for fridge freezer
(7)Boiler
(8)Upstairs lights
(9)Downstairs lights

 

[dingbat]

Now I'm not saying that RFC is better than a radial circuit - each has its own value. However, only in a very badly designed RFC would the amount of copper used be more than a radial circuit.

Still no.

There are circumstances where the use of a purpose-designed ring makes sense - for known, fixed, evenly distributed loads over long distances, for instance. But for socket outlets in a domestic installation, you will always use more copper if you install rings. (I never mentioned and would never use 4 sq mm, which appears to be the basis for your thesis.)

 

[PrenticeBoyofDerry]

Would you not consider using 4.00mm on radials for supplying circuits to uttilities and the garage work shop, bearing in mind the protective device rating will offer you more current?