what are your thoughts guys

[chrish_1977]

Done an eicr on a 2 bed flat, all good apart from the sockets, it's a radial, wired in 2.5 t+e (25 sockets in total), on a 20 mcb, zs was 2.72 ohms, I've checked against bgb and its over the maximum permitted zs, customer now wants it sorted, but I'm wondering what you guys would think is the best way to go about sorting this out. Choices I can see are, splitting the radial into two, or splitting into two and making the longest leg a radial.
The whole flat has just finished being decorated and all carpets down etc

 

[chrish_1977]

Tried all the tightening and stuff, that was my first try when I was testing.

That's why I thought about splitting it up, if possible of course

 

[davethsparky]

You could apply an RCD to provide additional protection as you would with a TT system. seeing as its a socket circuit it would benefit from RCD protection anyway.

Obviously this wouldn't be the way to solve this if it was a new install, but from the point of view of improving an old install I see no reason not to apply the RCD method.

 

[shagbite]

Debate mcb, or add rcd protection are two ways to increase te
maximum permissible zs.

if its rcd protected then Dont worry.

trouble is, i would worry. i couldn't leave an installation with such a high Zs just because it's RCD protected.

 

[jamie-spark]

An rcd can be used to provide fault protection on a tn system where the EFLI is to low enough to repeated mcb within the prescribed disconnection time
See
411.4.4
411.4.9

 

[chrish_1977]

But surely all reasonable steps must be taken to get the reading down, not just say "don't worry cause its got an rcd so the max zs is 1667"

I'm hope I'm not sounding a bit righteous, but I think doing that is the wrong way to go with it

 

[chrish_1977]

Debate mcb, or add rcd protection are two ways to increase te
maximum permissible zs.

if its rcd protected then Dont worry.

trouble is, i would worry. i couldn't leave an installation with such a high Zs just because it's RCD protected.

I would have to agree with you shagbite

 

[davethsparky]

But surely all reasonable steps must be taken to get the reading down, not just say "don't worry cause its got an rcd so the max zs is 1667"

I'm hope I'm not sounding a bit righteous, but I think doing that is the wrong way to go with it

I wasn't saying you should take a don't worry cos its got an RCD attitude. But you said the place had just been decorated and new carpets layed so the chances of you being able to install any new cabling are quite low. If the client is happy for you to be installing new cableing and the potential damage to the new decorations then that is definately the way to go.

The RCD is a fall-back soloution if the client refuses to let you disturb the new decorations to install new cables as they will inevitably be of the opinion that it 'works so therefore is not a problem' and not worth disturbing the decoration which in their eyes is far more important than mere electrical safety.

 

[Sharpend]

You say a flat, How is it wired? T/E, conduit?
If conduit is it not possible to pull additional cables in to either give a ring or enable to split further to two radials?

 

[chrish_1977]

If it was in conduit, then I would be happy, but alas no, good old chased

 

[LeckyBill]

Rcd protection 1667 ohms.

what??

i thourt that as well - cowboy?

 

[Sharpend]

I presume that you tested on the terminals not via the socket fronts themselves. It is common for older sockets to wear and the contact is less good resulting in poor readings.
Secondly, when you say you tightened all joints did you re-terminate the cables or just literally tighten? It could be that re-terminating would improve the readings.

Thirdly, change out the MCB to a 16a. If the circuit is not feeding kitchen appliances, only the remainder of the flat then a 16a may well be sufficient.

 

[chrish_1977]

Yep took all the sockets/sfs off and checked on terminals, and yes re terminated all of them too, the circuit just does the flat, but only sort if the kitchen, but even that us more the diner side of kitchen. Looks like 16A mcb is going to be the way forward

 

[telectrix]

Yep took all the sockets/sfs off and checked on terminals, and yes re terminated all of them too, the circuit just does the flat, but only sort if the kitchen, but even that us more the diner side of kitchen. Looks like 16A mcb is going to be the way forward

is there RCD protection on the circuit already? if so, try this. temporarily bridge out the RCD and retest using the hi-current range on your MFT. you may then get an acceptable Zs.

 

[jamie-spark]

But surely all reasonable steps must be taken to get the reading down, not just say "don't worry cause its got an rcd so the max zs is 1667"

I'm hope I'm not sounding a bit righteous, but I think doing that is the wrong way to go with it

Yes I would agree to an extent.

it's not always possible in comercial / industrial where applications require C/D curve mcbs and the EFLI is not low enough. Then an rcd/ echo would be used, and a further check to make sure it complies with section 434

 

[jamie-spark]

Although the "magic rcd" does not cure all ills. People do seem to think it solves All problems. I even know someone who omitted MPB because house was protected by 30ma rcd