two radials into an RCBO

[John-SJW]

No spare ways in the consumer unit. There are two low current radials on their own RCBOs. Do the regs forbid putting the two radials onto the same RCBO - that is two L wires into the one RCBO?

 

[John-SJW]

It's an argument as old as time, but my take is...

The interpretation of 314.4 is all down to how you define a final circuit.

If the regulation was meant to mean a final circuit will consist of a single line conductor in the case of a radial and two line conductors in the case of a ring, then this is what they should have said.

In my mind a final circuit is exactly what a competent electrician had designed it to be, accounting for design characteristics and manufacturers instructions. Therefore, as spurs are permitted, where and how the electrician decides to make a spur is not restricted by 314.4.

There is no ambiguity in 314.4. The final circuits must have own RCBO or MCB.

A final circuit is any circuit whether it is a ring or radial, with any of them with branches, spurs, etc. It is clear in the writing of 314.4 they cannot be connected to one way.

 

[telectrix]

There is no ambiguity in 314.4. The final circuits must have own RCBO or MCB.

A final circuit is any circuit whether it is a ring or radial, with any of them with branches, spurs, etc. It is clear in the writing of 314.4 they cannot be connected to one way.

but if you have 2 radials off 1 MCB, then those 2 radials combined are, by definition, 1 final circuit.

 

[loz2754]

There is no ambiguity in 314.4. The final circuits must have own RCBO or MCB.

A final circuit is any circuit whether it is a ring or radial, with any of them with branches, spurs, etc. It is clear in the writing of 314.4 they cannot be connected to one way.

Maybe you're confusing cables with circuits.
A circuit can consist of more than one cable connected to the source.

 

[GBDamo]

There is no ambiguity in 314.4. The final circuits must have own RCBO or MCB.

A final circuit is any circuit whether it is a ring or radial, with any of them with branches, spurs, etc. It is clear in the writing of 314.4 they cannot be connected to one way.

You arguing a logical fallacy, an argument from authority.

You claim there is no ambiguity where the constant debates on this subject clearly reveal otherwise.

Rather than state, as fact, "there is no ambiguity" you should say "I see no ambiguity" which is fine, its a personal opinion and one your entitled to.

If you could add a technical reason why this practice is unacceptable then fine but at the moment the argument seems to me to be "I don't like it and the regs say you can't do it".

 

[timhoward]

When I originally mentioned this reg on this post, I said this was fine and happens a lot, there is one reg to be mindful of, and asked the question - "can the two legs be considered one circuit".
The last bit is key, as very often they can, but sometimes they can't legitimately be classed as one circuit due to ccc or ocpd requirements.

For example, at a recent EICR I found an unlabelled 30 amp rewireable fuse, testing showed it fed a sub main to a shed and apparently strangely two sockets in a utility room. Take front off board and find a 6mm and a 2.5mm live in the same fuseholder. One might logically guess the 2.5mm was a radial for the two sockets. In fact it was yet another radial for a boiler FCU. (the utility room sockets turned out to be a joint box off the 6mm)
In that situation I had no issue citing 314.4 as one reason it wasn't adequate, the ocpd wasn't suitable for the boiler circuit and the whole lot was downright confusing. Definitely two circuits in the same fuseholder.

But if the same OCPD is needed, the same CCC, and the total loading is suitable, it clearly becomes one circuit in my mind.

 

[brianmoooore]

Yes, as I can read and interpret English. It says final circuits must have their own way (mcb, RCBO).

This is the crux of the matter. You ARE interpreting the wording incorrectly.

 

[John-SJW]

You arguing a logical fallacy, an argument from authority.

You claim there is no ambiguity where the constant debates on this subject clearly reveal otherwise.

Rather than state, as fact, "there is no ambiguity" you should say "I see no ambiguity" which is fine, its a personal opinion and one your entitled to.

If you could add a technical reason why this practice is unacceptable then fine but at the moment the argument seems to me to be "I don't like it and the regs say you can't do it".

The text:
314.4 Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board

What don't you understand about the clear English 314.4 is written in?

 

[John-SJW]

Maybe you're confusing cables with circuits.
A circuit can consist of more than one cable connected to the source.

I am confusing nothing.

 

[westward10]

When I originally mentioned this reg on this post, I said this was fine and happens a lot, there is one reg to be mindful of, and asked the question - "can the two legs be considered one circuit".
The last bit is key, as very often they can, but sometimes they can't legitimately be classed as one circuit due to ccc or ocpd requirements.

For example, at a recent EICR I found an unlabelled 30 amp rewireable fuse, testing showed it fed a sub main to a shed and apparently strangely two sockets in a utility room. Take front off board and find a 6mm and a 2.5mm live in the same fuseholder. One might logically guess the 2.5mm was a radial for the two sockets. In fact it was yet another radial for a boiler FCU. (the utility room sockets turned out to be a joint box off the 6mm)
In that situation I had no issue citing 314.4 as one reason it wasn't adequate, the ocpd wasn't suitable for the boiler circuit and the whole lot was downright confusing. Definitely two circuits in the same fuseholder.

But if the same OCPD is needed, the same CCC, and the total loading is suitable, it clearly becomes one circuit in my mind.

I don't see the difference.

 

[GBDamo]

This is the crux of the matter. You ARE interpreting the wording incorrectly.

I wouldn't say incorrectly exactly just a little lacking in nuance.

Both sides of this debate are, after all, opinions.

I mean, if he follows his opinion he will never leave an unsafe situation but may limit the customer's options.

 

[westward10]

This has been debated many times no harm in doing it again but can we keep it friendly.

 

[GBDamo]

The text:
314.4 Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board

What don't you understand about the clear English 314.4 is written in?

You're just shouting the same thing louder.

A final circuit, in my opinion, is any number of suitable conductors fed from the same OCPD.

Then you are into the realms of good workmanship and following manufacturers instruction.

A ten legged radial all in one MCB = crazy.

A two legged radial in one MCB = perfectly acceptable.

Any technical objections yet or are we sticking to the sophistry?

 

[pc1966]

Don't put a SPD on to a RCBO, use a MCB if the SPD type demands some form of OCPD below the DNO's fuse rating (many larger SPD are fine up to 125A or similar fuses).

• Firstly it is very likely to trip it on any modest surge event (as only 30mA equivalent to earth needed, averaged over the response time of the RCBO), disabling the SPD, and obviously taking out whatever other stuff the RCBO was feeding.
• Secondly there is a grater chance of the RCBO electronics being damaged if it has to divert a 10kA or more spike, even if only for tens of microseconds.

 

[Intoelectrics]

The text:
314.4 Where an installation comprises more than one final circuit, each final circuit shall be connected to a separate way in a distribution board

What don't you understand about the clear English 314.4 is written in?

The crux of this lies in whether its acceptable to spur from the supply source of the final circuit to extend the circuit.
Consider this, would it be acceptable to spur off the circuit cable inside the CU using an appropriate junction connection?

 

[UNG]

If it said each final circuit type must have it's own MCB it would probably make more sense, you wouldn't connect a socket or cooker circuit and a lighting circuit on the same MCB