Multiple Cables in a single circuit breaker

[SimpleSimon]

You enter both to denote its use and clear confusion but it does not mean it is 2 circuits, it still is classed as 1 circuit, same if you took a spur of a ring main to feed a boiler, you could write it as ring main + boiler but it is still one circuit regardless if it is jointed at the mcb terminals or via a spur.

Cool. Thanks for clearing that. I also would have classed this as two seperate circuits.

 

[Darkwood]

Cool. Thanks for clearing that. I also would have classed this as two seperate circuits.

The OCPD itself denotes the circuit of which the wiring after it is included regardless of its methods or whether it supplies multiple loads as long as it complies of course. Its often confused because we are taught in a fashion when discussing circuits we tend to express lighting circuit, bell circuit etc ... its a natural tendency to keep them separate in our heads even when supplied from the same OCPD, it contradicts they way we visualise circuits hence this always does the rounds every year as a thread.

 

[baldsparkies]

The definition of an electrical circuit.

An assembly of electrical equipment supplied from the same origin and protected against over current by the same protective device.

So if its 1 radial, 2 radials, or even 3 radials.

Once connected to a single mcb, the above definition applies and thus they become one circuit.

And that's what the lads have been saying all along,

Just need to work out where regulation 314.4 fits into this, because it does state.

Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energising of a final circuit intended to be isolated.

 

[Darkwood]

The definition of an electrical circuit.

An assembly of electrical equipment supplied from the same origin and protected against over current by the same protective device.

So if its 1 radial, 2 radials, or even 3 radials.

Once connected to a single mcb, the above definition applies and thus they become one circuit.

And that's what the lads have been saying all along,

Just need to work out where regulation 314.4 fits into this, because it does state.

Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board. The wiring of each final circuit shall be electrically separate from that of every other final circuit, so as to prevent the indirect energising of a final circuit intended to be isolated.

You answered your own question... the regulation is simply stating that separate circuits should be solely connected to their own OCPD and not for instance having the ends of a ring main connected across 2 mcb's..... this is all this regulation is stating 'do not have 1 circuit fed from multiple OCPD's or isolation of one may not be enough to prevent it remaining or becoming energised via another.

 

[baldsparkies]

That's spot on Darkwood.
We now have a post that answers all aspects of a question clearly, conclusively, and not leaving any member or visitor in any doubt.
No sarcasm (well not much) or abuse (well maybe a little) or attitude (well sometimes)
Anyway,
Thanks to all for clearing this one up. :icon12:

 

[GB.Kayak]

If in doubt I also have the spice girls to back me up!..

Its just one of those things that gets mis-interpreted so often it becomes believeable, but if you were right in your thinking then the whole design and layout of test certs would allow for multiple results from one OCPD if you think about it, ignore all the pen pushes half of them don't have a clue trust me I've corrected many of them before, if your in any doubt consult the IET themselves.

Since when have the spice girls been an authority of 'things electrical'? I have no love for the likes of the NICEIC but I would consider what their personnel have to say on the issue of circuits before consulting the spice girls ... though they would come a close second! ;-))

However, sir, I must despite being very much the junior in terms of experience challenge your long held interpretation. Note App 15. I recognise that its status is informative but it shows 2 types of circuits, neither have more than one ring or single radial wire exiting the OCPD! Furthermore, they are headed ring final and radial final circuits. They do however both allow 'An unfused spur may be connected to the origin of the circuit in the distribution board.'


While it may be possible to connect "more than one 'final' circuit", in your terms one final circuit with multiple wires, into an OCPD, and indeed very economically sensible to do so, it does make even a well installed DB incredibly difficult to 'read' without documentation! Unless the wires are labelled it becomes impossible to immediately identify what belongs to what. I had a situation the other day with 2 radials wired into the same OCPD. The OCPD rating is not a conclusive guide! A ring or radial circuit can be run in 4 mm2 cable from a 30 A or 32 A OCPD. If the radial circuit is 'doubled up' how would you know that it is just that without a great deal of time consuming investigation!

 

[Knobhead]

The sooner a moderator shuts this down the better.

 

[tazz]

I think this has now be answered