Ring final & Radial circuits off one mcb ?

[Soulsurfer]

Another straight forward job today has turned out to be a right mess once again so I thought I'd get some thoughts on the following before I start !

So an old MK LN59 board, feed to garage sockets on a single 2.5mm t&e from a 15A mcb and also spurred to feed a boiler on S plan,

Next ring final on a 30A feeding upstairs sockets as usual but on cover removal I found a 4mm t&e spurred from same 30A mcb and feeding opposite side of garage to sockets all on the 4mm then at the end spurred from last socket with 2.5mm t&e to feed new water cylinder via a DP switch !

Obviously I'm not happy with the 4mm being spurred as an extra circuit from a separate circuit pd but surely the immersion being spurred from sockets is rough too ?

Never seen anything like that before !

 

[Risteard]

Sorry Risteard didn't even realise I had done that, gone now

LOL. Fair enough. I wasn't sure what I'd said to upset you!

 

[Des 56]

 

[Wilko]

... Next ring final on a 30A feeding upstairs sockets as usual but on cover removal I found a 4mm t&e spurred from same 30A mcb and feeding opposite side of garage to sockets all on the 4mm then at the end spurred from last socket with 2.5mm t&e to feed new water cylinder via a DP switch ...

Hi - my post beverage take on this - BYB App 15 gives guidance on how rfc and radial ccts are to be arranged. They are separately shown and I take that to mean they should not be mixed. So I think the arrangement Soulsurfer found is not in accord with BYB. If I was to connect an rfc and radial to the same mcb and present it to a QA I would expect earache

 

[Risteard]

Hi - my post beverage take on this - BYB App 15 gives guidance

Exactly - it is guidance. Appendix 15 is informative, not normative, and therefore does NOT form part of the Wiring Regulations.

 

[Wilko]

Exactly - it is guidance. Appendix 15 is informative, not normative, and therefore does NOT form part of the Wiring Regulations.

Got that, thanks.
But I'm not clear - are you saying I've interpreted the information incorrectly ?

 

[Marvo]

Well its not diverse at all. Its one circuit but could easily be 2 circuits. 2 circuits would offer diversity. 1 circuit doesn't.

It's better to avoid the term diversity unless your applying it as the true electrical definition.

It's probably poor circuit design that could provide inconvenience for the installation user.

I'd also agree with Dave that a ring and a radial final (and any other installation arrangement) from the same OCPD should be considered as being a single circuit for technical purposes.

 

[Soulsurfer]

Rough as it definitely is, there are at least 2 ways spare in the existing cu where ocpd's could have & should have been fitted and avoided this ! Thanks to all for your opinions though as whichever way individuals interpret the BYB it is certainly not something I'd want to show my assessor as my work on a visit !

 

[davesparks]

Though the interpretation is such, I think its a bit daft. I've often come across one mcb protecting a number of "different" circuits. Tested them and recorded them as individual which to me makes sense (I could be completely wrong of course), even though I'm well within the regs to just record the highest readings of which ever "circuit" produces them.

If necessary you can record the two parts of the circuit on separate lines of the schedule of test results but identify them as being the same circuit.
I do similar to record all the necessary information for a lollipop circuit

 

[davesparks]

Hi - my post beverage take on this - BYB App 15 gives guidance on how rfc and radial ccts are to be arranged. T

They are just the standard circuit layouts which are a quick and easy circuit which can fulfill the basic requirement of installing general use sockets.
They are not a guide to the only way or preferred way to install a circuit, a competent person can design a compliant circuit in any way they wish.

 

[westward10]

Debatable whether someone who whacks another circuit onto an existing one is competent, different standards eh.

 

[davesparks]

We've been there before on this Dave my view won't change.

I don't remember that, but ok.

What definition of a circuit do you use?

 

[westward10]

I don't remember that, but ok.

What definition of a circuit do you use?

Was some time last year when I joined the forum went on for days. I read Reg 314.4 to mean two final circuits should have individual circuit protection and I won't sway from that. In the OPs case and probably nearly every situation like this a new circuit has just been tagged onto an existing circuit even if spare ways are available, to me the intention has been to create a new circuit and by connecting in this manner does not suddenly mean the two circuits now become one. To me this is just poor installation methods.

 

[Generator]

The Regs are based on the common sense application of established electrical principles (physics). That's the best place to start. Then check the regs for something you might have missed. I regard a 'circuit', when connected to a point of supply, as
any combination of cabling and equipment fed from the same point.
Firstly, all the cabling should be sized adequately for the maximum load it will carry
AND have a short circuit rating at least equal to the protective device to which it is connected. In the case of multiple loads ie sockets, a suitable diversity factor can be applied to the loading calculation. That calculated load should then not exceed the load current rating of the protective device.
Secondly, when the circuit comprises more than 1 parallel 'sub circuit', each one would need to be assessed separately for earth loop impedance, referred to the single protective device.
The circuit described sounds a bit dubious, but, could meet the regs if the above logical requirements are met.

 

[westward10]

What exactly is a parallel sub circuit.

 

[Toneyz]

May meet the regs but bad workmanship