Jumping to conclusions...

I had a similar thing. A 2.5 cable in a duct started tripping the RCD. I never found the fault because it was under concrete, but the fact that the cable wouldn't pull through was a clue. There was some differential subsidence that had cracked the concrete so I'm supposing that the duct and cable were damaged.

At one time all the outdoor circuits here were on the same RCD, and that caused much wasted time, so I separated them off into five circuits each with its own RCD.

Bill

So you replaced the 1.5mm2 T&E with the same and upgraded the single socket to a double.....

I'd be using 4mm2 or 2.5mm2 with a 20A MCB for that doubel socket...

(I am assuming the SWA is 4mm2 or higher)

No, I replaced it with 2.5mm^2 since that was handy...

Its a moot point though, since the SWA feed is 1.5mm^2 (although it is a XLPE SWA, and the termination points are metalclad - so is actually rated for 27A)

Its fed from a 16A MCB.

The whole circuit was originally only provisioned for lighting, the socket was a later addition.

The change to a double socket does not really have much bearing on things since in practice it won't carry a high load in both sockets at any time. The cable is adequately fault and overload protected both by the MCB and also has overload protection courtesy of the notional 20A design load imposed by a socket (I will ignore the additional 12W of lighting!)

If you do the design on the circuit[1], then it is in spec and meets its disconnect times for L to N faults. The only marginal part with the change to a double socket, is if you fully loaded it with long term loads, then you would risk tripping the MCB.

No, see above.

It's one of those cases where if installing again from scratch, I would design differently since the use case has changed, however it is adequate as it is, but has no capacity for expansion.

In message <snfkbp$12lb$ snipped-for-privacy@gioia.aioe.org>, SH snipped-for-privacy@spam.com writes

I'd use one of these

Yup, good plan. I did something similar by moving all my outside and outbuilding circuits to their own CU, as well as their own RCDs etc. So in a worst case situation I could turn the whole CU off to isolate the lot.

So you have a 16A MCB on 1.5 mm2 SWA feeding a double gang socket feeding a EV granny charger occasionally....?

thats some nice underfloor heating for the lawn/driveway (assuming you've buried it) as I didn't think 1.5 mm2 was actually rated for 13A continuous load?

I?m gonna guess that John has done all the sums.

Tim

Over 10? of 1.5mm2? Probably not a lot. ;-)

Tim

Yes, in reality that's what I did, following Adam's instructions.

Bill

Very occasionally (like once or twice a year) yup.

Have a look at:

The SWA is clipped direct, not buried.

(and most granny chargers are less than 13A load)

Could I suggest you do the sums, rather than just guessing? :-)

So for a 12m cable with 11A that would be 3.8V. Well within the 5% (11.5v) permitted for a power circuit. Since this is also a lighting circuit, then one could argue it should be within the 3% (6.9V) limit - which it also is.

There is also 12m of SWA with the same CSA feeding it - hence why I did not bother using anything larger initially.

its probably I am so used to doing:

domestic lighting circuits in 1.5mm2 on a 6A MCB / RCBO

and doing 2.5mm2 radials on a 20A MCB / RCBO for appliances

and 2.5mm2 ring mains or 4mm2 radials on a 32A MCB /RCBO

SO I would never dream of allowing 11A continuous load through 1.5mm2 cable :-)

you might not, but the regulations allow it.

Back in the late 1970's early 1980s it was common for 1.5mm T&E from a

I do not think that anyone does that these days.

When I bought the current house, all the lighting was on 1.0mm1 T&E and traditional filament GLS or halogen GU10 bulbs everywhere

I replaced all the 1.0 mm2 T&E for 1.5 mm2 T&E and swapped out the filament bulbs for 8 watt LED GU10s or SESes.