On 02/07/2020 14:08, wrote:
On 02/07/2020 12:28, No Name wrote:
Yup, there are practical advantages to not having a RCD at the head
end. The 18th edition requirements to RCD protect all "unprotected"
cables though can make it harder to implement in a compliant way when
there is a run of T&E feeding the start of the SWA.

That is the situation I currently find myself in and need to work out
the best way forward:

When the house CU was changed, a new 6mm2 T&E was run from the new
consumer unit to the garage between a floor and ceiling void. This is
fed by a 32A Type B RCBO.

The original intention was for a car charging point.

20 metres of 10mm2 SWA has now been laid from the garage to the
outbuilding & greenhouse. A TT rod has been installed and this has
10mm2 protective conductor single core wire attached to it.

A 45A cooker switch has been used to connect the end of the 6mm2 T&E
to the start of the 10mm" SWA and this is in the integral garage.

A plastic flame proof IP67 sub-consumer unit will be fitted in the
outbuilding to the other end of the SWA. THis will use all RCBOs like
the main house consumer unit comprising of 2 off 6A RCBOs and 2 off
20A RCBOs

Now I need to change the 32A RCBO in the main house CU to avoid double
tripping of two sets fo RCBO's in teh event of a fault at the
outbuildings

So what to change it to:

32A Type C RCBO

That gives no discrimination.

Time delayed 32A RCBO

That would be ok.

100mA 32A RCBO?

Again, little or no discrimination.

Or to a simple 32A MCB as the 6mm2 run of T&E is only about 7m long
and is either in a ceiling/floor void or surface clipped.

S.-

Is there anything that prevents you putting the surface-clipped section
into earthed conduit and using a B32 MCB?

Oddly, the surface clipped section being "visible" does not need
additional protection. So as long as the section in the ceiling void is
safe from nail penetration to a depth of 50mm or greater, then the plain
MCB is fine.

(ceiling void normally treated as reference method B, giving a nominal
38A capacity for 6mm^2 T&E)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/