Rewiring upstairs lighting circuit

[TomSparkman]

Hi everyone,
I am to rewire the upstairs lighting circuit as the old switches, pendants and cables are outdated.
The existing consumer unit is old but still has mcb's rather than rewirable fuses, but NO RCD protection.

The first question is, does the new replacement circuit HAVE to be RCD protected? I'm pretty sure it does, as my new cables will be chased in to the walls but NOT 50mm deep (obviously in prescribed zones)

Second question, rather than put a whole new CU in as this may introduce problems with the other circuits, would it be good practise to mount a small garage CU next to the existing CU? This garage CU would have a 30Ma RCD and space for two mcb's.

Third question is, what would be a suitable way of feeding the garage CU? And a suitable means of isolation?
My thoughts were to double up the tails in to the load side of the main isolator with the existing CU and to terminate the earth in to the earth bar in the existing CU.
Another option which is possible would be to split the existing tails between the 100 fuse and the existing CU and surface clip to the garage CU roughly a meter away.The flaw in this is that I would have to remove the main fuse, which is obviously bad practise.

Thank you in advance for any advice

 

[Octopus]

For what it's worth I probably wouldn't do the job unless the customer agreed to new cu and bonding first.

 

[dave274]

if they don't want a new consumer unit then stick an rcd fcu next to the cu and run the new circuit through it.

 

[egg67]

By the time you've messed around doing all that it will be quicker and cheaper just to change the CU as your going to rewire the up stairs lighting Circuit you should not have byroad neutrals, as for the main fuse just pull it out or get the DNO to pull and put it back in when your done

 

[J.C.E]

If the customer isn't going to go for new fuseboard/ bonding etc- feed a fused RCD spur from the current mcb that currently does the upstairs lights- then supply your re-wired upstairs lighting circuit by the new fused RCD unit- therefore it provides additional protection and o/c protection then just issue a EIC for the 1 circuit.

 

[TomSparkman]

Thanks for the fast responses!
I definitely don't want to go down the route of the new CU as I'm on a short time scale and if problems occur because of the old wiring on the other circuits I haven't got time to sort it.
The most suitable option for me sounds like going from the existing old mcb with a 1.5 t/e, in to the rcd fused spur with a 5A fuse in it, on to the upstairs lighting

Would this be deemed as good workmanship?

 

[dave274]

I'd put a 13a fuse in the fcu personally.

 

[TomSparkman]

Fair enough, just out of interest and without being disrespectful why would you put 13A in?

 

[egg67]

Before you do a CU change you would have tested everything so will know if a problem exists and then can Factor that in to your time scale, I'm not saying you have to change the CU but I just think at the end of day if your re-wiring up stairs lights in stead of messing about do it right that Way when they get you back to re-wire the next Circuit it will be a lot easer for you

 

[dave274]

If you put a 13a in then chances are it's not going to blow and it will save the home owner looking for a fuse in the dark.

 

[TomSparkman]

Ahh, I see your point!

 

[J.C.E]

Just explain to the customer the different options and the advantages/disadvantage of doing it that way- and then its up to them- you can only give them your opinion

 

[SS-2015]

I would probably put RCD FCU in as it's easiest - Have you checked to see if you can replace the MCb with RCBO?

 

[TomSparkman]

I would probably put RCD FCU in as it's easiest - Have you checked to see if you can replace the MCb with RCBO?

I did think about that bit not sure of the compatability due to the age of the existing board. However before I start the job ill get a look in at what make the board is and try and find one that fits. If that fails the the RCD fcu is the next option.

 

[TomSparkman]

Just explain to the customer the different options and the advantages/disadvantage of doing it that way- and then its up to them- you can only give them your opinion

Yes I'll do that, after all they're the ones paying for it!

 

[DanDobson]

If the 13A fuse is in the RCD FCU will there not be a diversity issue as the new RCD FCU will be fed by the current 6A upstairs MCB?

May have mis-read above so ignore me if I have

Dan

 

[telectrix]

If the 13A fuse is in the RCD FCU will there not be a diversity issue as the new RCD FCU will be fed by the current 6A upstairs MCB?

May have mis-read above so ignore me if I have

Dan

EVEN WITH A 5a FUSE, YOU WILL GET DISCRIMINATION PROBLEMS AS THE 6a mcb WILL MOST LIKELY GO FIRST.

 

[DanDobson]

EVEN WITH A 5a FUSE, YOU WILL GET DISCRIMINATION PROBLEMS AS THE 6a mcb WILL MOST LIKELY GO FIRST.

Yeah good point Telectrix, how should the OP get round that issue then?

 

[telectrix]

i'd not bother. stick a 13A fuse in as the cable is adequately protected by the 6A MCB

 

[J.C.E]

And if your planning of re wiring the whole circuit anyway (new circuit from db) bonding will need to be in place anyways and to issue a eic regardless of upgraded the db or not.￾