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.