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?

 

[MrPupsi]

Is absolutely fine.

 

[DefyG]

that is two L wires into the one RCBO?

Fine, you'd put 2 into same terminal if part of a RFC.

 

[timhoward]

It happens a lot and will be fine.
Regs wise I don't think it's the answer you want:
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

Can you consider them to be one final circuit with a spur that happens to be at the CU?

 

[John-SJW]

It happens a lot and will be fine.
Regs wise I don't think it's the answer you want:
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

So best to join them via a J box with one cable running into the RCBO. Cludgy, not as good, but within regs.

 

[John-SJW]

Fine, you'd put 2 into same terminal if part of a RFC.

I know, but the regs can defy themselves.
On the same note. I see some SPDs that fit onto the CU busbars. Some have their own dedicated 32A mcb, other makes say it is best to wire it into an adjacent RCBO/MCB, as it is difficult to have it off when on a used circuit. So, can three wires be screwed into an RCBO? Two ring circuit wires and one SPD wire.

 

[littlespark]

Fine as long as the OCPD size is right. 16 or 20A for 2.5mm 32A for 4mm
Then it’s one radial circuit with a branch off at source.

 

[7029 dave]

What fuse rating is this RCBO

 

[John-SJW]

What fuse rating is this RCBO

6A Two 2.5mm cables.

 

[littlespark]

6A

So are they lighting?
We should try not to put all lights in the same circuit, so one fault doesn’t wipe out everything….

 

[John-SJW]

So are they lighting?
We should try not to put all lights in the same circuit, so one fault doesn’t wipe out everything….

One radial is a small fridge, one a boiler. Both together consume well under 6A with many amps to spare. My query was about two radials into one RCBO.

 

[littlespark]

Well, the answer is the same. As long as cables and OCPD are suitable, then it’s one radial circuit, with a branch off at source.

 

[7029 dave]

One radial is a small fridge, one a boiler. Both together consume well under 6A with many amps to spare. My query was about two radials into one RCBO.

It will be classed as one 6 AMP circuit

 

[John-SJW]

It happens a lot and will be fine.
Regs wise I don't think it's the answer you want:
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

Can you consider them to be one final circuit with a spur that happens to be at the CU?

A 2.5mm cable can be taken from the RCBO to a FCU next to the CU. Then daisey chained off to the boiler, which has its own local FCU. Then the fridge cable off the FCU near the CU. One cable only into the RCBO and DP isolation for the fridge. It would be a radial to the boiler with a sub radial off that to the fridge. Sorted.

 

[timhoward]

A 2.5mm cable can be taken from the RCBO to a FCU next to the CU. Then off to the boiler, which has its own local FCU. Then the fridge cable off the FCU near the CU. One cable only into the RCBO and DP isolation for the fridge. Sorted.

You certainly can if you like, but it's not actually required as per other posts as it is legitimately one final circuit with a branch.
There isn't a right answer here - we'd all prefer not to add joints if not required, and we'd prefer not to stick two legs in an RCBO.
I'd probably gravitate to the latter option personally.

 

[brianmoooore]

I thought we'd laid this one to rest a couple of months ago!
Doesn't matter how many wires from however many radials connect to one MCB or RCBO, as long as their total cross sectional areas doesn't exceed the maximum capacity of the device's terminal and they are all properly secured. They will all form ONE circuit in total.
Connecting multiple radials like this can make fault finding much easier. The last case of RCD tripping I sorted out was caused by a lighting circuit with six individual wires connected to the MCB. Within ten minutes of arriving at the property I'd identified the wire with the poor IR, connected the other five back up, been around the house to see what didn't work,and discovered it was the feed to the light in a boiler house.
Problem was a leak in the shower in the room above directly above the conduit to the switch.

 

[timhoward]

@brianmoooore I agree in this case, and must have missed the previous thread on this.
Out of interest, would your comment mean that 314.4 can never actually be broken if combining radial circuits?

 

[John-SJW]

The idea is to make a way for an SPD by joining two circuits. The SPD will be a single way unit. The BG SPD looks OK. Can it fit into a Wylex CU?

Type 2 Single Phase SPD (Surge Protection Device) | BG (CUSPDT21-02)

 

[brianmoooore]

By the letter of the regs. , no, but it depends if you're an engineer or a sheep. I have no problem mixing different makes in a full DIN rail CU, as long as they fit properly.
This doesn't connect to the busbar, so no pulling out of shape. The only possible issue is to make sure the front part projects through the front panel enough to meet the IP rating, which it almost certainly will.

 

[SJD]

I'd make one more comment - perhaps the reason the boiler and the fridge were on separate radial circuits was because they are either (a) somewhat important circuits that could be problematic if tripped, or (b) the loads (at least the boiler or associated valves/pump) are prone to faults. I know most properties don't provide that luxury, pity to take it away.

 

[GBDamo]

Whenever I swap out a board I look to put everything on its own OCPD and leave space for expansion, so there's often more breakers than the original board.

However if I come to a full board, needing a low power radial, I'll always put it to the customer that I can do a "Spur at source" (which some electricians frown on) or I can put in a new board and a dedicated OPCD.

Guess which option they choose.

 

[John-SJW]

You certainly can if you like, but it's not actually required as per other posts as it is legitimately one final circuit with a branch.
There isn't a right answer here - we'd all prefer not to add joints if not required, and we'd prefer not to stick two legs in an RCBO.
I'd probably gravitate to the latter option personally.

It would also give DP isolation to an integrated fridge.

 

[timhoward]

Is this Wylex single module type 2 SPD of any interest:

Wylex NMT2SPD3W/1 Surge Protection Devices

Buy Wylex NMT2SPD3W/1 Surge Protection Devices online at Shop4 Electrical & get FREE Next Day UK Delivery when you order by 2pm & spend £60

www.discount-electrical.co.uk

It is a bus-bar connection too....no breaker needed for it

 

[John-SJW]

I'd make one more comment - perhaps the reason the boiler and the fridge were on separate radial circuits was because they are either (a) somewhat important circuits that could be problematic if tripped, or (b) the loads (at least the boiler or associated valves/pump) are prone to faults. I know most properties don't provide that luxury, pity to take it away.

People like a fridge on their own circuits so if another circuit is at fault the fridge is not taken out,

 

[John-SJW]

Is this Wylex single module type 2 SPD of any interest:

Wylex NMT2SPD3W/1 Surge Protection Devices

Buy Wylex NMT2SPD3W/1 Surge Protection Devices online at Shop4 Electrical & get FREE Next Day UK Delivery when you order by 2pm & spend £60

www.discount-electrical.co.uk

It is a bus-bar connection too....

The Wylex is £70 (taking the mick) to BGs £38. If two radials are joined there is another way available. Not sure if the BG will fit a Wylex.

 

[7029 dave]

People like a fridge on their own circuits so if another circuit is at fault the fridge is not taken out,

But your adding the boiler to this circuit ?, so it is not on its own anymore.

 

[timhoward]

The Wylex is £70 (taking the mick) to BGs £38. If two radials are joined there is another way available. Not sure if the BG will fit a Wylex.

In my experience it's usually the bus bar alignment that is the biggest issue, which as someone said wouldn't apply to an SPD which connects to an MCB.

 

[John-SJW]

By the letter of the regs. , no, but it depends if you're an engineer or a sheep. I have no problem mixing different makes in a full DIN rail CU, as long as they fit properly.
This doesn't connect to the busbar, so no pulling out of shape. The only possible issue is to make sure the front part projects through the front panel enough to meet the IP rating, which it almost certainly will.

The BG can fit onto a Din rail. Not sure if it fits a Wylex busbar, or any busbar.

"Can be fitted on DIN rail directly into the consumer unit."

 

[John-SJW]

But your adding the boiler to this circuit ?, so it is not on its own anymore.

Yep. A compromise.

 

[westward10]

@brianmoooore I agree in this case, and must have missed the previous thread on this.
Out of interest, would your comment mean that 314.4 can never actually be broken if combining radial circuits?

I always follow this, it is two final circuits therefore separate circuit protection.

 

[timhoward]

The BG can fit onto a Din rail. Not sure if it fits a Wylex busbar, or any busbar.

"Can be fitted on DIN rail directly into the consumer unit."

Sorry if we are at cross purposes, or I'm stating the obvious, but the BG has the earth connection at the bottom, and doesn't connect to the bus-bar at all.
With these circuits merged do you have way free or two, as the BG SPD also needs an > B16 MCB .

(The Wylex module does connect to the bus bar and only needs one way total.)

 

[John-SJW]

Sorry if we are at cross purposes, or I'm stating the obvious, but the BG has the earth connection at the bottom, and doesn't connect to the bus-bar at all.
With these circuits merged do you have way free or two, as the BG SPD also needs an > B16 MCB .

(The Wylex module does connect to the bus bar and only needs one way total.)

Thx. Never looked in detail. The Wylex looks the business then. The Wylex's only protection is the main incomer fuse? mmmm

 

[UNG]

People like a fridge on their own circuits so if another circuit is at fault the beer in the fridge is not taken out getting warm,

Fixed that one for you

 

[John-SJW]

Sorry if we are at cross purposes, or I'm stating the obvious, but the BG has the earth connection at the bottom, and doesn't connect to the bus-bar at all.
With these circuits merged do you have way free or two, as the BG SPD also needs an > B16 MCB .

(The Wylex module does connect to the bus bar and only needs one way total.)

Some makers do not recommend an SPD has its own RCBO/MCB, as a dedicated MCB can be left off by mistake. An essential circuit will not be left off, so they recommend it is taken off one of these. They recommend the SPD is taken off an adjacent 32A RCBO/MCB. That may mean three wires into the terminal of an RCBO, which is against the regs as posted here.

 

[westward10]

Some makers do not recommend an SPD has its own RCBO/MCB, as a dedicated MCB can be left off by mistake. An essential circuit will not be left off, so they recommend it is taken off one of these. They recommend the SPD is taken off an adjacent 32A RCBO/MCB. That may mean three wires into the terminal of an RCBO, which is against the regs as posted here.

It is not the fact it may be left off. You need to contact the manufacturer as to whether the spd needs external circuit protection. If you are retro fitting one I suggest you provide external protection otherwise you are interfering with the manufacturers internal configuration which may well go against Regulations.

 

[Dartlec]

The idea is to make a way for an SPD by joining two circuits. The SPD will be a single way unit. The BG SPD looks OK. Can it fit into a Wylex CU?

Type 2 Single Phase SPD (Surge Protection Device) | BG (CUSPDT21-02)

View attachment 86813

Surge Protection Devices sell various ones (Available at some CEF), and the answer I had from them at a trade show a while back is that because it's not on the busbar it is not necessary to 'match' the make of the switchgear for type testing requirements. They do specify a separate MCB though.

Wylex may give a different answer, but SPDs one sounds fair enough to me.

Their (SPD's) technical manager, Katie I think it is, clearly knows her stuff - she's been on some of the E5 podcasts and sits on one of the IET panels I believe - They were one of the first to introduce an SPD before any of the CU makers had one widely available...

 

[brianmoooore]

Doesn't apply to fridges quite so much, because they have a light inside and are opened fairly frequently, but I always try to make sure a freezer is on the same circuit as something else important, such as the wi fi router or TV. That way, if the circuit has tripped out, it will be noticed fairly quickly.
Similarly, I always connect smoke alarms to the same circuit as the most frequently used lights.

 

[brianmoooore]

Out of interest, would your comment mean that 314.4 can never actually be broken if combining radial circuits?

Splitting the ring and leaving both sections connected to the same MCB/RCBO doesn't break 314.4 in itself - it's just two radial circuits from the same source, but the breaker will have to be reduced from 32A to a maximum of 20A, and consideration made as to whether that is likely to be sufficient without experiencing overload. For those reasons, it's often preferable to split into two separate circuits.

 

[nicebutdim]

Doesn't apply to fridges quite so much, because they have a light inside and are opened fairly frequently, but I always try to make sure a freezer is on the same circuit as something else important, such as the wi fi router or TV. That way, if the circuit has tripped out, it will be noticed fairly quickly.
Similarly, I always connect smoke alarms to the same circuit as the most frequently used lights.

When fitting decorative accessories in the kitchen & utility room, I decided to use isolator switches with neons for fridge & freezer. I know those neons will eventually fail, being permanently illuminated, but I like the reassurance of knowing that glow means all is good.

 

[John-SJW]

Splitting the ring and leaving both sections connected to the same MCB/RCBO doesn't break 314.4 in itself -

It clearly does:
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

 

[loz2754]

It clearly does:
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

Not necessarily. A final radial circuit can be wired as a tree with multiple branches, one or more of which branches could be connected to the same way, so it is still only one radial circuit.

 

[John-SJW]

Not necessarily. A final radial circuit can be wired as a tree with multiple branches, one or more of which branches could be connected to the same way, so it is still only one radial circuit.

It clearly says that one radial (final circuit) needs its own way.

 

[GBDamo]

It clearly says that one radial (final circuit) needs its own way.

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.

 

[littlespark]

Doesn’t #40 answer your own question?

I agree with #43 above

 

[John-SJW]

Doesn’t #40 answer your own question?

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