Russell Edwards said:

I've never seen a supply with its own dedicated MCB before but that's probably just my lack of knowledge / experience. what are you hoping to achieve that the master fuse doesn't dare I ask?

My new house supply will be from the 3-phase intake in the garage, so I have little choice. Any EVCP will be supplied from the main DB and the kitchen will have its own supply, so I don't have to allow for a cooker either.

With only one bend, you might just get 2 x 25 mm² + 1 x 16 mm² down some (25 mm) conduit. I include the CPC because I would want a certain earth continuity path.

Again with only one bend, you don't need a bender - you can buy pre-formed ones which screw on.

How about flexible galvanized conduit?

I ever finish the new supply, it will be on a 63 A MCB.

Won't you risk loosing discrimination with downstream MCBs/RCBOs on faults?

   - Andy.

There won't be any faults! 

Seriously, I don't really see why there should be any faults in the fixed wiring. It is a risk which I am prepared to take.

Chris Pearson said:

My new house supply will be from the 3-phase intake in the garage, so I have little choice. Any EVCP will be supplied from the main DB and the kitchen will have its own supply, so I don't have to allow for a cooker either.

That makes a lot more sense now. I did something similar with an Annex a few years ago, As I'm OCD about things I chose to add a selective / Time delay RCD to the situation to make sure I'd got most edge cases that pure current based protection might not catch if the earth connection was poor.

according to Doncaster 6181Y in 25mm has an OD of 12.5mm so no way you're getting 2 of them down some 25mm OD conduit. If I go single insulated then they might just fit but it'd be making a lot of work for myself in routing the conduit.

I agree about not using conduit as the earth that and you've read my mind on that front.

Russell Edwards said:

according to Doncaster 6181Y in 25mm has an OD of 12.5mm so no way you're getting 2 of them down some 25mm OD conduit. If I go single insulated then they might just fit but it'd be making a lot of work for myself in routing the conduit.

Quite so. I have just measured some 6491 (B or X) at 8.8 mm diameter.

I think that you have answered your own question concerning conduit.

My thoughts

I do a lot of work around Swindon, I would say 40% or more of the many new houses have standard  tails running through the fabric of the building without additional protection.

If you are running the tails through the loft space, say clipped to beans or something, away from the ceiling below I wouldn't consider them buried in the fabric of the building to depth of less than 50mm. Inside a wall is at a depth of more than 50mm. 

My understanding is that using SWA is so that nails etc come in to contact with the earthed armour and live conductor at the same time, SWA is never going to stop a nail or a screw, it will just go through a gap in the strands.If SWA is used (not sure RCD protection is required, need to check the regs). thinking logically if the cable is damaged fault current will be connected to the armour and not the person holding the drill. I would think the pragmatic approach is protection by a 100mA time delayed RCD, it's what I have done in the past anyway.

If you can get conduit in, could you buy some 3mm thick capping from a steel merchant and use this instead, I am informed this is what some house builders do.

Then I would have a switched fused isolator in a steel case, mounted in the meter cabinet, proteus is about the smallest I have found, then replaced the switch with the RCD. Get rid if the DNO's isolator switch as it's not required any more, SSEN have a policy where they allow registered electricians to break the fuse seals provided they replace them and apply a sticker with  their details to the fuse. EV installers end up cutting the seals on fuses in over 50% of installs, there is no way the DNO's can keep up.

Tails from the meter to the fused switch, swa terminated in the fused switch.

Only really need to be concerned if the SWA is going to be at 90C where it's terminated. If loft insulation etc is increasing temperature is there enough cable run between the insulation and the terminations to dissipate the heat.

Most EV' charge points end up being connected to a seperate DB close to the incoming supply, tails split in henley blocks inside the meter cabinet. All depends on where the EV charge point will be located. In general a separate DB aliviates thermal issues  with RCBO's over heating due to constant load and proximity of other loaded devices. Typical RCBO at full load dissipates 15 to 20 watts. 

I have a similar issue to deal with on Friday. 10m run either under the plaster of a dot and dab wall or inside a ground floor ceiling. Whatever I end up doing will be better than the current situation with the DNO's cable running under the plaster board protected by a 315A fuse.

How about a short length of pyro or even a pair of pyro single cores.  These can be installed into tight spaces and the terminations dont take up much space.  Having solid copper sheaths they wouldnt need an RCD.  A pair of 16mm singles would do it from a rating point of view or paralel arrangement of smaller sizes might be easier to install than a 2 core 16.  They could be terminated in an adaptable box adjacent to the CU if there isnt space for the glands on the CU.

This looks like an interesting project.

What is the Peak demand for the property?

100A Switch Fuse 1P+N Complete with 100A,80A & 63A Fuses are available.  If your peak demand was say 50amps the a KVM(100A Switch Fuse)  with a 63A Fuse would help.  100A Switch Fuse will allow you to properly terminate the SWA. I assume a 3 core SWA 25mmSquared CSA.  If XLPE - Thermosetting Pvc Insulation then that give current rating of 124 Amps which allows for derating.   Next step to RCD or Not RCD the 4 meter of SWA burried in the fabric.  BS7671 says yes it should be.  So a S type or time delay RCD with the KVM.  This would then bring into play a single point of failure for possible nuisance tripping of the RCD.  Change the 30mA RCD to a 100mA or even 300mA at the KVM.  Then at the CU/DB 30mA RCBOs.  With all the above considered get an SPB type 2 or 2/3 added to the CU/DB.

Sergio - Next step to RCD or Not RCD the 4 meter of SWA burried in the fabric.  BS7671 says yes it should be.

Sorry what regulation number are you referring to? Doesn't a swa have a metallic sheath? 

Regards,

CPC

No need to rcd sub-mains in SWA or steel conduit or similar unless TT supply...
M.