Offer: day's paid work for tutor/mentor/electrician (house bashing)

[Simonslimline]

Agree with all the above Hence me stressing that CPS membership was not required. On the other hand, I do want to do things "by the book" as far as LABC is concerned. Start as you mean to go on, eh?

I've sent Dillb a message, including my cable calcs, which I may as well post here as well so you can all pick holes in it

Calcs:

TN-C-S, measured Ze = 0.10 ohms.

4.1kW double oven (hobs are separate, gas).

No diversity (oven only, not a cooker), so Ib=17.83A.
In>=Ib = 20A, BS EN 60898 type B MCB (RCD protected)
No rating factors
It>=Ib (fixed load), but let's provide overload protection too so It>=In

Reference method C: buried in plaster from CU to beneath boards (no insulation), then under boards, through brick wall into kitchen, then clipped direct to existing 20A switch in kitchen unit.

H05V2V2-F (2.5mm, 3 core) flex from switch to oven.

Estimate cable run CU to existing switch ~ 10-11m, allow 12m.

From table 4D5 (p364, BYB):

CCC: 1.5mm = 20A; 2.5mm = 27A; 4mm = 37A.
VD: 1.5mm = 29; 2.5mm = 18; 4mm = 11 (all mV/A/m).

So 1.5mm would in theory be fine for both CCC and VD (=6.2V, assuming 12m). Blimey!

2.5mm will definitely be fine for this oven.

Going to suggest putting 4mm in. Totally over the top for this oven, but allows us (or more likely next owners of house) to put in full electric cooker if they need be (upgrade OCPD to 32A). But will defer to Dillb's advice if he thinks this is silly.

Expected R1+R2 (from OSG table I1 and using 1.2 factor from I3 for operating temperature), assuming 12m run:

1.5+1.0mm: 12x30.2x1.2 = 0.44 ohms
2.5+1.5mm: 12x19.51x1.2 = 0.28 ohms
4.0+1.5mm: 12x16.71x1.2 = 0.24 ohms

Zs (above values + Ze of 0.1 ohms) all within maximum Zs of 2.19 ohms (table 41.3, BYB).

R1+R2 of flex not taken into account of above, but even if it was, would still be fine.

CU is Wylex 16th edition board (split board, half protected by 30mA RCD). Spare ways in RCD-protected half (even got 20A MCB unused in there).

All you have top do now is run the cable terminate and test, Building who?

 

[pennychew]

I think you are right to get dillb in to give you a hand, it will be good to see how it's done correctly and bounce some ideas off him to get a 'real world' perspective, for instance most sparks I know would just stick a cooker circuit like that on 6mm t+e and use the same for the cooker outlet to the cooker rather than buy 4mm flex like it often says in the instructions, you'll learn a lot more face to face with someone experienced while carrying out the job

 

[Plonker 3]

Steve, Imhave got your PM And will reply to you later.

I Have about 12 meters of 6mm t&e in the garage if you wish to use that free of charge as it was left over from a job I did and is already paid for.

 

[happysteve]

This is just getting better and better.

 

[Paul.M]

This is just getting better and better.

Yeah this is a good thread, forum lads helping each other out in the real world yet again.

Steve dont get too excited yet, Dillb charges £300 per day + VAT

 

[happysteve]

And I'm sure he'll be worth every penny...