minor works cert for new circuit doubled up from an existing mcb??

[Engineer54]

Well I`ll bow to superior knowledge. Seems amazing to me that, in theory, you can put a single socket outlet supplied via a new 2.5mm cable into a 32amp MCB supplying a ring, call it a junction box and issue a MWC but hey ho.

NO Taffy, the 32A breaker wouldn't be able to protect the 2.5mm cable, in the same way as you would need to use a FCU to spur off a ring if you use a single 2.5mm cable.

You Can however connect another ring circuit to that single protective device, as then the 32A breaker will satisfy the circuits protection requirements, and as long as it satisfies the other circuit requirements, such as disconnection times etc, ...it complies!!!

As i've said, not the best of practices, and one that i would hope you rarely if indeed ever see, but it does comply!! lol!!!

EDIT.... Just realised that you can spur off a ring for a single socket!! Just shows you, how often i've allowed spurs off of ring circuits on my projects ...lol!! On the rare occasions i have, it's always been via FCU. I don't like seeing spurs on rings at the best of times....lol!!

 

[Guitarist]

Engineer54, have you never run a spur off a ring main as a single 2.5mm t&e cable? I feel like I'm missing something here...

 

[Guitarist]

Thanks for the edit Engineer54. Thought I was losing the plot for a minute there...

 

[TaffyDuck]

OK thank you guys. I fully understand the electrical aspect but I have to admit that through-out my time as a sparky I have never known this. Whenever I have come across arrangements like this in a CU during a PIR I`ve always flagged it up and I can honestly say I`ve always issued EICs for the work when Ive used an already used MCB
But I`m man enough to admit I dont know everything so thanks again, I`ve learned something new today.

 

[Guest112]

we learn new things every day clearde it up for me also thanks everybody

 

[telectrix]

think it's p21 of the brb. definition of a "circuit". ain't unwrapped the bgb yet, for what it co9st, think i'll display it at the tate.

 

[ample current]

I was told by my tutor that if you connect a new light circuit to the mcb of an existing lighting circuit it is deemed a new circuit.
I remember this because i was marked wrong in my assessment because i said it was altering an exixting circuit.

 

[Engineer54]

I was told by my tutor that if you connect a new light circuit to the mcb of an existing lighting circuit it is deemed a new circuit.
I remember this because i was marked wrong in my assessment because i said it was altering an exixting circuit.

Sounds like yet another lecturer/tutor that doesn't know too much about what he's teaching!! lol!!!

 

[telectrix]

I was told by my tutor that if you connect a new light circuit to the mcb of an existing lighting circuit it is deemed a new circuit.
I remember this because i was marked wrong in my assessment because i said it was altering an exixting circuit.

well, you were correct. your tutor was wrong. see post 26.

 

[TomTrundle]

When you alter an existing lighting circuit protected by an MCB, so long as your alteration is to BS 7671 there is no requirement to upgrade the MCB to RCBO. Is that right?

 

[telectrix]

if your new work requires RCD protection in order to comply ( e.g if you are burying cable in a wall < 50mm deep etc., etc.) then you must either fit RCD/RCBO to the circuit, or an RCD FCU to your new work.

 

[GT1]

interestingly the diagram on page 425 of BGB shows socket outlets wired downstream of an FCU wired in 1.5mm....
Makes perfect sense when thought about, but woulve triggered a trip to the van to check the book if i'd found it on PIR (ECR)..!