how long is a piece of string

[JohnW2]

If you did a "rewire", why did you feel it necessary to reinstall Rings rather than instal Radial wiring with individual RCBOs at the Consumer Unit?

Quite apart from the fact that you are asking questions about something which happened over 17 years ago, the most obvious answer to that was that installation of ring finals has been essentially 'standard' in the UK for the past ~70 years (and even more so 17 years ago than today), and it is only 'relatively recently' (probably no more than a couple of decades or so) that people have started questioning that 'established practice' and moving back in the direction of radials.

Kind Regards, John

 

[EFLImpudence]

Since the general usage of MCBs?

After all, one could now have two 25A radials (method C, of course) with the same cabling as one ring.

 

[ericmark]

If we follow the idea that any non portable appliance over 2 kW should be on a dedicated circuit then with Immersion, Oven, Washing machine, Tumble drier, and dish washer all on dedicated circuits yes one can get away with 16 amp radials. So looking at this house as an example, two washing machines, two dish washers, stand alone cooker, and a hob, two electric showers, and immersion heater, three floors so at least 4 radials for sockets, kitchen would need it's own, three lighting circuits, and supply to out building that is without putting heating on it's own RCBO, that's 17 RCBO's. So to have an isolator and SPD needs a 22 slot board.

So board costs £100 to start with. £126.65 with vat. £11.82 for the RCBO with vat, and £28.20 for the SPD. So £356 for the consumer unit, and your trying to sell this when you know other electricians are going to be quoting for a double RCD 12 way from likes of Screwfix at less than £100, yes maybe I would go for that with my own home, but to be competitive it going to be a hard sell.

Got to Hager instead of Fusebox and the price doubles again.

There is a problem with the ring final, too much load at ends can cause an overload, but in general for most installations the ring final is the way to go, it has been for last 70 odd years, the other problem with 16A radials is either you use type C or with type B anything with a large motor can trip the RCBO, same with welding sets. So that leaf blower will no longer work.

You try telling a house owner it's not some thing wrong with the installation it is his welding set, leaf blower etc which is at fault, even if it works OK in his mates house and worked OK in this house until you rewired.

Using radials is simply too much cost and hassle.

 

[EFLImpudence]

If we follow the idea that any non portable appliance over 2 kW should be on a dedicated circuit then ...

The regulations do not say that - plus

dedicated does not mean separate.

 

[ericmark]

Since the general usage of MCBs?

After all, one could now have two 25A radials (method C, of course) with the same cabling as one ring.

Two very short 25 amp radials, looking at 24¼ meters each compared with 106 for ring final maximum length of cable to be within the volt drop permitted. So with many homes need 4 radials for every one ring final.

 

[EFLImpudence]

The volt drop regulation isn't mandatory either.

 

[ericmark]

The regulations do not say that - plus

dedicated does not mean separate.

OK the appendix suggests it rather than being a rule. And you can run three 2 kW appliances from a ring final and it is unlikely it will every trip, but with a 20 amp radial there is a much higher chance they will be used together and trip the MCB/RCBO.

So yes a 4 mm² cable to a grid switch which in turn feeds an array of kitchen appliances is permitted, have you tried getting 2 x 4 mm² into the terminals of a grid switch? Technically not a ring, just two conductors in parallel, but far easier to wire that grid switch with 2 x 2.5 mm² then feed the appliances.

It does matter where the CU is, mothers house under the stairs, if it tripped easy enough to reset, here it is in the flat under main house, was a garage, so outside down a set of steps and then you reset, not some thing I want to do 11 pm in the snow.

 

[ericmark]

The volt drop regulation isn't mandatory either.

So if your a cowboy you can wire in radials, but some one who conforms with the suggestions given in the regulations book then he uses ring finals? That does not sound like you, you are no cowboy I am sure, so yes a small first time buyers house yes you can get away with radials, but once you move to larger homes the ring final has so many advantages.

 

[EFLImpudence]

Two very short 25 amp radials, looking at 24¼ meters each

Have you put your 25A worth of appliances all at the end of the cable?

 

[EFLImpudence]

So if your a cowboy you can wire in radials, but some one who conforms with the suggestions given in the regulations book then he uses ring finals? That does not sound like you, you are no cowboy I am sure, so yes a small first time buyers house yes you can get away with radials, but once you move to larger homes the ring final has so many advantages.

I merely said that one 32A ring could be two 25A radials - i.e. 50A - with the same cable which is true.

Obviously all the relevant regulations have to be considered.

 

[JohnW2]

Since the general usage of MCBs? .... After all, one could now have two 25A radials (method C, of course) with the same cabling as one ring.

One could, but 25A MCBs are not all that ubiquitous.

I'm happy with 32A rings or 32A (4mm², Method C) radials, and more-or-less happy with 25A radials (if/when MCBs to allow them exist) - but, as I've often said, I'm less comfortable with 20A (let alone 16A) radial sockets circuits. Although, in practice, even they are unlikely to get significantly overloaded, it just doesn't feel quite right to have a situation in which circuit supplying several sockets could theoretically be 'overloaded' by what was plugged into just one double socket (and certainly if the circuit served anything more than 'just one double socket').

If I were designing an installation from scratch today, it would probably all be 4mm² radials.

Kind Regards, John

 

[JohnW2]

Two very short 25 amp radials, looking at 24¼ meters each compared with 106 for ring final maximum length of cable to be within the volt drop permitted. So with many homes need 4 radials for every one ring final.

Quite apart from the fact that there are no regulations (only guidelines) relating to voltage drop (unless a circuit is supplying a load for which the product Standard specifies a minimum supply voltage), as I often say, it's an issue that I generally completely ignore - since (despite the anecdotes you often quote) I would think that it must be incredibly rare for any degree of voltage drop in a credible installation in a 'standard house' (or even a 'large house', like mine) to result in any 'problems'.

And, don't forget that, even if (for whatever reason) you want to stick to the 'max VD guidelines', the calculation you do assumes the most extreme of loading conditions of the circuit - which, in practice, is virtually never going to happen.

Kind Regards, John