rewiring 4 bedroom house

[ClearIncite]

I live in a 4 bedroom house (3 bed upstairs, lounge+kitchen+bed downstairs). It needs rewiring so I planned to run the upstairs off one ring main, downstairs off a second ring main and the kitchen off a third ring main (obviously the cooker on its own 32a radial). I haven't been in this line of work professionally for 8 years now so I've lost touch with the latest wiring regulations.

I was chatting to a sparky the other day who's currently working on some new houses. He said radial circuits are starting to come back in as the prefered method as opposed to a ring main and I should be using radial's all through my house. What do you guys think?

 

[EFLImpudence]

It depends on the circumstances, loads and cable routes.

Whichever is most suitable - no hard and fast rules.

 

[Iggifer]

I personally like the idea of breaking up an install into more radials rather than one ring. If I was having a re-wire, that would be my preferred method of install.

However, this provides you with no redundancy, if you have a break from C/U to socket one, you will lose the entire circuit. With a ring you will not lose power with the same fault, however you will not necessarily know you have a fault.

As has been stated, it's depends on circumstances and personal preference

 

[Chri5]

However, this provides you with no redundancy, if you have a break from C/U to socket one, you will lose the entire circuit. With a ring you will not lose power with the same fault, however you will not necessarily know you have a fault.

Madness, are you suggesting a broken ring fused at 32 amp is good? You are aware 2.5mm te as a radial can take 26 amp thus the situation you suggest gives a cable overload?

 

[riveralt]

I live in a 4 bedroom house (3 bed upstairs, lounge+kitchen+bed downstairs). It needs rewiring so I planned to run the upstairs off one ring main, downstairs off a second ring main and the kitchen off a third ring main (obviously the cooker on its own 32a radial). I haven't been in this line of work professionally for 8 years now so I've lost touch with the latest wiring regulations.

Perhaps the main issue is the fact that such work is notifiable and if you intend to do the work yourself you must speak to your Local Authority Building Control before you start any work.
You cannot do the work yourself and then get a registered electrician in to test alone, he/she will have to have been involved in the whole process from the beginning.

I was chatting to a sparky the other day who's currently working on some new houses. He said radial circuits are starting to come back in as the prefered method as opposed to a ring main and I should be using radial's all through my house. What do you guys think?

I don't think radial final circuits ever went out of fashion.
As has already been stated work out your demand and design your circuits accordingly - with redundancy in mind.
I completed a rewire a few months ago on a two storey four bedroom property which had two individual radial final circuits for the bedroom and landing sockets. Each circuit was protected by its own 20Amp RCBO.
Three double sockets per bedroom and one for the landing. The circuit design and bedroom layout allowed each bedroom to have at least two sockets on different radials.
Electric shower on its own radial.
Downstairs the kitchen was on its own ring final circuit with individual radials for the oven/cooker and the fridge/freezer.
The two downstairs rooms each had their own 20Amp radials but with sockets shared in a similar way to the bedrooms.
Three lighting circuits - for the front of the house rooms, the rear of the house rooms, the outside security lights and the mains/battery smoke alarms circuit.
I also added several other specific circuits.
All circuits RCBO protected on a fourteen way board.
This particular house and the expected demand lent itself to this approach. Each property will be different.

 

[Iggifer]

No of course I'm not suggesting it's a good thing, my wording was possibly not as clear as it could have been.

However this is the nature of a ring final, i'm sure there are 1000's of them out there with problems that go undetected.

This is why I personally prefer the idea of radials. Fault finding is generally much simpler

 

[ban-all-sheds]

What do you guys think?

I think, nay, I know, that if you don't know enough about the advantages and disadvantages of the two types, and which is best suited to your needs, then you can't possibly know anywhere near enough to rewire a house.

 

[ebee]

Both Ring finals and radials each have their merits and drawbacks compared to each other.

I suspect that if rings had not been invented years ago and had therefore not been in widespread use by now then if someone were to invent them today they simply would not take off.

However they are here and lots of us use them or often a combination of both are chosen in many installations.

 

[ban-all-sheds]

I suspect that if rings had not been invented years ago and had therefore not been in widespread use by now then if someone were to invent them today they simply would not take off.

I'm utterly sure that they would be regarded as dangerously unsound.

 

[ericmark]

Oddly my son and I were talking about which system to use in his house. And yes we have a lot of items in the house which if invented today would never be allowed. The whole idea of using gas for cooking to start with.

With my house if doing a rewire I would use radials and RCBO's but with my sons house he has a TT supply so as a result want double pole protection so the idea of twin RCD's seems more likely method. Although also considering a 100ma main RCD with 30ma RCBO's.

The cost of a MCB means radials and rings have a very small price difference and where the house is rewired a room at a time then radials do make it easier. But with RCBO's the cost is something to consider.

The other point about RCBO's is they do from time to time trip with no real fault like any RCD. Splitting the house into many circuits can result in a circuit failing without realising it has failed. Where there is something which is relied upon to work like cordless phones, fridge, router, or freezer splitting into many circuits can be a bad move. It took me about 15 minutes to realise my phones had stopped working due to a RCD tripping and when I did realise I reset it without thought about the freezer on the same circuit and since auto defrost or as it puts it frost free I have no idea if anything defrosted or not.

So still not sure if radials is good or bad? I have never loaded a ring high enough for a 32A MCB to ever trip even when whole house was on a single ring. Other than kitchen we don't really put much load on a ring and likely two radials one up and one down on 20A MCB would never trip if items over 2kW have their own dedicated supply. i.e. washing machine, tumble dried and dish washer.

However what I would question is if the volt drop requirements could be met with radials? Very few people sit down and calculate the volt drop or loop impedance before wiring and so I would think having two rings is likely safe method of ensuring when tested it does pass. I hesitate at calling the kitchen supply a ring. Often two 2.5mm cables feed a grid switch which in turn feeds washing machine etc. However since both 2.5mm cables are the same lenght and feed one grid switch they are really two conductors in parallel rather than a true ring.

The other point that worries me with radials is fitting for example a 20A MCB per room will mean the consumer unit will have many breakers so could quite easy end up overloading the DNO fuse or where 63A RCD's are used the RCD could become overloaded. Two 32A breakers feed from a 63A RCD will never overload the RCD but four 20A breakers could.

In a normal domestic it is unlikely ever to be overloaded but we read here of people running business from home and then it would be easy to exceed the 100A without opening any MCB.

 

[ebee]

"Although also considering a 100ma main RCD with 30ma RCBO's"

Providing your 100mA RCD is time delayed and the RCBOs are double pole (NE fault will not be cleared by a single pole RCD).


"But with RCBO's the cost is something to consider. "

A few years back they were £50/£60 each + VAT but larger production runs now make them more viable.


"The other point about RCBO's is they do from time to time trip with no real fault like any RCD."

?

"However what I would question is if the volt drop requirements could be met with radials? Very few people sit down and calculate the volt drop or loop impedance before wiring and so I would think having two rings is likely safe method of ensuring when tested it does pass."

Agreed

"The other point that worries me with radials is fitting for example a 20A MCB per room will mean the consumer unit will have many breakers so could quite easy end up overloading the DNO fuse or where 63A RCD's are used the RCD could become overloaded. Two 32A breakers feed from a 63A RCD will never overload the RCD but four 20A breakers could. "

Not often a problem with a straight domestic, the total current draw at any time will not alter for any given situation irrespective of how many or how few circuits one has even though the potential for this to happen increases with more circuits. The exception of course is by an abuse such as mentioned here with the business use as you point out

 

[bernardgreen]

However this is the nature of a ring final, i'm sure there are 1000's of them out there with problems that go undetected

I wonder how many radials have a failed CPC that has gone un-detected for years. Afte all the circuit supplies power and hence appears to be be OK even though the earth is missing on some of the sockets. At least with a ring there has to be two breaks in the CPC before any sockets lose the CPC.

Also with a ring final a loose live or neutral termination on a socket is less likely to burn on current passing through and onto another socket as the other leg of the ring will take the current. Using 2.5 mm and 20 Amp breaker that is fault tolerant and safe, ( or 4mm and 32 Amp )

A radial would be safer if the CPC at the furthest socket was returned to the consumer unit earth bar via a single green-yellow of suitable cross section.

 

[ebee]

In other words a radial that has high integrity earth siutable for computers therefore a ringed cpc has the benefits of a cpc on a ring final but the other benefits of a radial on Ph & N.
Good thinking Bernard

 

[ebee]

Anyone got a reel of twin & two earths?

 

[bernardgreen]

In other words a radial that has high integrity earth siutable for computers therefore a ringed cpc has the benefits of a cpc on a ring final but the other benefits of a radial on Ph & N.
Good thinking Bernard

I was thinking more of the safety function of the CPC and not the low noise functional earth ( the so called high integrity ) earth that large computor systems require. Low noise on the safety earth to the computor is necessary to prevent noise currents flowing in data circuits between computors connected to different earths. Often a direct ground rod is used to earth computor frames rather than the safety earth of the lectical supply. ( Yep it is a can of worms ). I have lost count of the number of times it has been necessary to install some form of galvanic separation in data and speech lines between systems where one or both have been earthed to noisy CPCs.

The true high integrity earth is the earth that is garanteed to be there to protect users of equipment from electrical shock when the equipment they are using become faulty or is abused ( by being washed with a hose pipe for example )