Non standard circuit

[SLIPSHOD & SLAPDASH]

Whilst testing at a house that we are carrying out various jobs on i found an unusual ring circuit. The householder wired the entire property himself 52 years ago. For some odd reason on one ring he took 2 cables in & out of each socket, meaning 4 cables in each termination. So really its not a ring (although it is) more like a doubled up radial. Its wired in a mixture of imperial 7/029 & 2.5mm Twin & earth with a 30A BS3036 fuse which i was going to change for a 32A Rcbo. Its a bit late now (nearly 2am) & i am thinking, is this actually ok ?

 

[ElectekAir]

How did he manage to terminate 4 in the sockets? never tryed but 3 is hard enough

I am sure there is somthing in the regs saying that you cannot have more than 2 cables in a mcb or maybe it is just NIC?

 

[ianmacd]

How did he manage to terminate 4 in the sockets? never tryed but 3 is hard enoughI am sure there is somthing in the regs saying that you cannot have more than 2 cables in a mcb or maybe it is just NIC?

That sounds like an NIC thing as you can spur of a ring anywhere including at the MCB.

As long as you can prove a ring (or even 2 ) then that is ok. I would be temped to try and split it into radials though and stick them on 16's.

 

[ElectekAir]

That sounds like an NIC thing as you can spur of a ring anywhere including at the MCB.As long as you can prove a ring (or even 2 ) then that is ok. I would be temped to try and split it into radials though and stick them on 16's.

I meant in the mcb there should only be two cables? not 3 or 4

 

[PC Electrics]

You mention changing the ocpd to an RCBO from a 3036. Since there are no retrofit RCBOs for 3036 carriers this hints at a board change. Is this so?

Assuming it is a board change, then you are only responsible for ensuring the circuit is safe and adequate for the new protective device. Even though it is "double wired" and this is certainly odd, if it is truly a ring circuit then it is adequate and can go on a 32A device.

If you suspect that some of these double legs may "criss cross" the ring, or some of them may be spurs on spurs, then I would suggest reducing the new device rating to 20A. With the cable sizes present this assures they are protected.

To be able to map out exactly how this circuit is put together would presumably require considerably more inspection and testing, which the client may not wish to pay for. You could take the safe option of a 20A device and note why on your EIC.

Unfortunately one cannot put every little "anomoly" right - no-one would ever pay us to do so. Neither should you over-think it. I know, your professional curiosity wants to find out what's going on here, but unless you can find out quite quickly you may have to let it lie.

 

[PC Electrics]

Ians suggestion of splitting it into two radials sounds good, but I'd make it 2 x 20A.

There is no reg in BS7671 which says there is any limit to how many conductors may be connected into an MCB. Though from a practical point of view I'd suggest 4 to be a sensible limit.

 

[NozSpark]

How the hell would you convert this mess into 2 x radial circuits???

it sounds like he's efectively taken both legs of the ring through each accessory and terminated both of them at each accessory!

 

[ianmacd]

I meant in the mcb there should only be two cables? not 3 or 4

There would be 3 if you spured a ring at the MCB.

 

[ElectekAir]

There would be 3 if you spured a ring at the MCB.

I was told 2 only :_| been moving CCT's around ever since:_|

 

[Riggy]

I was told 2 only :_| been moving CCT's around ever since:_|

When you were told this were you given a reason?

 

[ElectekAir]

When you were told this were you given a reason?

If i remember somthing to do with the design of the MCB's Clamp not holding the middle cable properly, well at least smth like that.

I would like to know other peoples views on this because i would like to know:|

Edit: Sorry to the OP i have hijacked this thread but will start a new one

 

[sellers]

its in the brb, spurring from the mcb is fine, meaning 3 cables is fine aswell.

 

[green-hornet]

its in the brb, spurring from the mcb is fine, meaning 3 cables is fine aswell.

I would also check any manufacturers lit about this, I have seen some very loose connections made at the MCB because one of the cables has not been firmly clamped. Thats beside the ones clamped behind the clamp, but that was me :innocent , which I found before energising the system.

 

[binky]

If i remember somthing to do with the design of the MCB's Clamp not holding the middle cable properly, well at least smth like that.]

Only a problem if cables are different sizes. Personally i don't like to see more than 2 cables in an MCB, but it's not against regs., and very convienient at times.

 

[SLIPSHOD & SLAPDASH]

I found 5 cables terminated in one socket today. I told him he deserved a medal for that.

Anyhow, it turned out only the modifications he made in the 70's had this strange wiring arrangement so during some alterations we did today, this circuit was partially rewired and some cables through crimped in the back of the box's to make a true ring circuit.

There was only 2 cables at the fuse, he had then terminated both pairs at all the sockets.