Consumer Unit Upgrade

[IPS]

I am currently assessing the replacment of an exisiting fuseboard to a new split CU and seek advice that I'm unable to find reference to in 7671.

The exisitng fuse board is approximatley 8mtr from the Meter, does the new CU need to be repositioned closer to the meter and all the circuits extending? I have a maximum figure of 3mtr for the consumer tails length in my head

Thank you

 

[Vortigern]

The 3m rule is a DNO thing. You can fit an isolator and run SWA to the CU from the isolator to get around this. However if you bury it the wall you run afoul of needing RCD protection for the cable. So ideally the SWA would run surface.

 

[telectrix]

sure SWA buried in wall does not require RCD protection as it has an earthed metal armour cpc. 522.6.204 (i).

 

[bill01803]

I would look at fitting a board with RCBOs not split load

 

[DPG]

The 3m rule is a DNO thing. You can fit an isolator and run SWA to the CU from the isolator to get around this. However if you bury it the wall you run afoul of needing RCD protection for the cable. So ideally the SWA would run surface.

A switchfuse rather than an isolator.

 

[i=p/u]

Switched fuse is correct and appropriate installation method to suit

 

[IPS]

Many thanks for everybodys input, much appreciated.

Just to verify another point... The conducters are required to be 25mm2 from the Isolator to CU

 

[Strima]

Many thanks for everybodys input, much appreciated.

Just to verify another point... The conducters are required to be 25mm2 from the Isolator to CU

Depends on the DNO fuse size. But most people default to 25mm to cover for future supply upgrades which may change the fuse size to a maximum of 100 amps.

 

[Vortigern]

sure SWA buried in wall does not require RCD

I would have thought that, but NAPIT did an article in Pro Electrician that said you did/might in certain scenarios. I'll see if I can link it.

 

[Strima]

I would have thought that, but NAPIT did an article in Pro Electrician that said you did/might in certain scenarios. I'll see if I can link it.

The only time I can see RCD requirement for a general use distribution circuit is when disconnection times cannot be met, i.e. TT systems.

 

[Dustydazzler]

If it was part of a full rewire I would be inclined to manoeuvre the consumer unit much nearer to the meter if possible

save faffing about installing a metal clad swi fuse and 25mm swa which at the best of times is awkward to install

 

[richy3333]

Not worth running 25mm conductors as you will have to derate your fuse to meet selectivity requirements assuming the DNO fuse is 100A

 

[pc1966]

Closest regulation is 434.3 (iv)

SWA is obvious choice as no protection needed (within reason) but hard to wrangle, or you could have tails in metal trunking or conduit (though it would be hard to get cables though in 25mm conduit I expect).

 

[pc1966]

Mention of 3m is under 433.2.2(ii) and 434.2.1(i)

 

[IPS]

Sorry I am slighly more confused with the Consumer Tail sizes.
The DNO fuse is 100A TN-C-S earthing arrangement > 25mm Tails to Meter > 25mm Tails Meter to Isolator > I need to know what is the minimum size cable CSA from the Isolator to the CU.

Thank you in advance.