No pics sorry............

[Baddegg]

Went to view a kitchen refit this week, new kitchen and new rfc circuit dedicated to the kitchen, have a look at the CU and whilst inspecting I see that the 2 lighting circuits, up & down, are both wired with the same 1mm 3&E cable (pre 2005 cable)
Red as line to down mcb, yellow to up mcb, blue to neutral bar and earth to earth bar,
I am relatively new to this game but I’ve never seen that before and the customer says she’s never had any problems with it,ask for any old paper work and the cert (won’t mention the scams name) for a CU change doesn’t mention it but then it also says all IR readings were perfect ha ha!

 

[KennyKen]

had a bit of sunstroke earlier maybe that’s why I came across like a ----wit. I could have been diplomatic but seen this play out all to often....

 

[buzzlightyear]

had a bit of sunstroke earlier maybe that’s why I came across like a ****wit. I could have been diplomatic

mad dogs &English men !

 

[KennyKen]

Cor your not wrong!

 

[Devonchris]

I'm struggling to find anything seriously wrong with this setup. I'm assuming 2 6A SP Mcb's isolating the up and down L circuits. so what we have is a shared Neutral which is not uncommon. So without some rewiring they will both have to be on the same Rcd, which again in not uncommon.

I've seen similar done in the 1960's using singles to a central point which is then split to various circuits. It only means the neutral is joined further down the line rather than joined at the neutral bar.

Regarding safe isolation, without a DP MCB the only way to isolate the neutral is with the main CU switch. This set up doesn't alter that.

So what big problem am I not seeing here?

 

[Wilko]

Hi - with this arrangement you turn one MCB off to work on that circuit, but a light on the other circuit is on. You separate the shared N and you get a nice tickle.

 

[Wilko]

Then you say "that's not effen right" and touch it again. Never have I ever ...

 

[Octopus]

So what big problem am I not seeing here?

Turn off upstairs lights - downstairs are still on - you are working on the shared neutral ......................... ouch that hurt!

 

[Baddegg]

So just for arguments sake if we label the board accordingly does that make it comply? It is still a shared neutral after all.....

 

[Devonchris]

But in a conventional CU without DP Ocpd all the neutrals are shared. Hence the need for a safe isolation procedure.

What some of you seem to be saying is your failure to carry out safe isolation make the installation inherently dangerous?

 

[Toneyz]

had a bit of sunstroke earlier maybe that’s why I came across like a ****wit. I could have been diplomatic but seen this play out all to often....

Forgot to say welcome back to the forum Kenny

 

[Pete999]

Forgot to say welcome back to the forum Kenny

Yes Welcome back Kenny.

 

[Wilko]

But in a conventional CU without DP Ocpd all the neutrals are shared...

Yes, but no. The N are normally connected at the bar, but current in one circuit does not return to the bar via a different circuit's N (without a fault ). In the case here, one MCB is off, but the other MCB is putting current into the common N. If you put a tester on that N it may only have millivolts on it at that point, but separate the N and suddenly one end goes to full L via that load.

 

[telectrix]

Sumed up very well there Pete each skill set or niece of electrical work has its own set of skills although we are all putting in rings and radial circuits. The problem with these short courses is they may cram in everything academically with a limited practical but it doesn't replace a longer term on the job training. The OP will encounter these problems of existing installations on most occasions this is where experience & training comes in. How do you think the likes of Pete,Tel and even myself got over these issues before all the schemes helplines and internet forums.

simplesss. we blagged it.

 

[Baddegg]

That’s the stuff they can’t teach us in 5 weeks tel,nice one ha ha ha

 

[johnduffell]

single pole isolator is fine in TN systems, safe isolation procedure only checks the voltage between all conductors before separating them, no one would be testing for dead every time they separate a conductor. Maybe we should be using clamp meters on every conductor before separating?
To the OP perhaps the only responsible solution if you can't get permission to put on one circuit, would be to put a danger label so at least it's obvious two circuits need isolating before working on the cirsuit.