Clarification on addition/alteration to ring protected by BS3036 fuse

[WDMDL]

Had a look at a job today which involves some additional sockets to the ring and a FCU.
As it's protected by a 3036 I was looking at providing an RCD in separate enclosure adjacent to the existing metal clad CU.
Also the DNO/metering co have been in recently and installed a new meter and 100A cutout (tails are 16mmsq) and the proper spiral spring clip earth connection to the incoming cable's lead sheath... but between the new MET and the CU the earthing conductor is a pair of approx 6mmsq green insulated wires, so am I right in thinking that's going to need upgrading to 16mmsq.

MPBCs are 10mmsq to gas and water, so no problem there.

Regarding the CU, I believe the 3036 types have relatively low breaking capacities - is there reference data available for them so I can see what spec the setup is?
I haven't done any PFC tests yet, but did do a quick Zs at a socket at the back of the house that I'd be doing some of the work from and it was very low at 0.31 Ohm so I'm expecting Ze to be 0.1 or less, with PFC in the region of 2.5kA
If this is the case, am i right in thinking the work can't be done without a board upgrade too?

Thanks,

Simon.

 

[Dunc]

I would say upgrade the main earth to a 16mm is definitely something that needs doing. An RCD in a separate enclosure will be fine. 3036 fuses are rated at 1kA from memory, this doesn't necessarily mean they need upgrading due to the main fuse being rated at 33kA however i tend to bung a 60898 retrofit MCB as a matter of course. Can't see the CU needs upgrading unless there is signs of damage though this would be entirely different if it was a old timber Wylex unit.

 

[WDMDL]

Cheers Dunc,

Simon

 

[grimysparks80]

i tend to bung a 60898 retrofit MCB as a matter of course.QUOTE]

Great things if youre only doing a minor addition.

 

[malcolmsanford]

And so yet again we tend to ignore Reg Reg 543.1.1 espicially as if there is a spring clip onto a sheath I would imagine that this is a TN-S earthing arrangement.

The low Zs is not the sole indication you have a low Ze, if this is a TN-S system I would be amazed if you got a Ze of 0.1. Your low Zs could be the result of parallel path.