New garage electrics

[SUNRAY]

I've just been out to assist surveying for a little job, a Brand new brick Garage, the architects drawing/planning application shows an amazing amount of electrical infrmation: 6mm² 3C SWA feed from 40A rcbo in house, lighting cct 6A, garage power cct 16A with 6 DSSO, outdoors lighting cct 1.5mm² 12C SWA 6A and outdoor cct 2.5mm² 16A with 3 sockets.

So the builder has done a lovely job of the garage including laying in the cables under the new resin drive and a landscaping wall. The intended electrician is now not available due to a health issue.

However the builder made a mistake

The 2 larger coils of SWA looked the same and he has run the 6mm² for the lights which is not an insurmountable problem as garden and the 12C between house and garage under 15m of immaculate resin drive, only showing where it comes up through the understairs cupboard floor and garage floor, where all 3 come up together. Fair do's the builder quickly accepted the mistake and reluctantly accepts the drive may have to come up. There is a shortage of the resin at the moment.

There are no plans for anything unusual in the garage or garden, my first thought is to bunch the cores 4x1.5=6mm² and driving home we discussed.

What are others opinions?

 

[securespark]

It obviously isn't an oft-seen practice, but I reckon that would be acceptable.

Wonder what the tech guys at IET would conclude?

 

[SUNRAY]

It obviously isn't an oft-seen practice, but I reckon that would be acceptable.

Wonder what the tech guys at IET would conclude?

In reality it's just a parallel feed which is acceptable and no different to split con.

 

[securespark]

Yes, having thought about it further after posting, I came to the same conclusion.

 

[Adam_151]

I'm guessing the high core count on the 1.5mm was due to separate switched banks of lighting? How does that fare without that, client willing to forgo the functionality?

As to the submain, generally its not a problem, I'd want to be sure of the thermal protection to the cable in the event of a single 1.5mm core faulting to the armouring. I can't find the generic let through data for breakers over 32A, however if you were to assume a simplistic I²t being equal to PEFC² x 0.1 then you get a limiting value of 1.5kA being the max earth fault current at the supply end, if its less than this, you're fine, if not dig out the manufacturers I²t for whatever PEFC you have, and unless you are right on top of the transformer then likely you'll still be alright

 

[SUNRAY]

Trenches can be dug for the lighting with longer routes and more joints but all doable, in fact builder is probably there as I type.

The guy I'm doing this for/with was talking about PEFC on the drive home and said he'll check, we also discussed reducing it to 32A.