Garage wiring

[RaceDiagnostics]

Here is a job that needs looking into.

Garage wiring is on a radial circuit with a 32A breaker in the main CU with what looks like a 4mm conductor.

It comes out of the side of the house here, but no longer looks like 4mm, more like 2.5mm.

Comes into the garage here, definitely 2.5mm.

And then here is the CU in the garage.

Not too clever. I suspect the join will be under the bedroom floor just inside the wall.

Will need to lift the carpet and boards to have a look then extend the 4mm out to the garage.

 

[brightspark]

a bit of 6.0mm all the way back would have been better with a 40 amp mcb at the db giving you a 30 amp at garage consumer unit and a lighting circuit . it depends on what load you require and how much you want to spend on it

 

[sparkysy]

What are your plans for the future in the garage?
I would go bigger! 4mm singles in conduit will do 32a.
However 4mm twin and earth in conduit won't due to de-rating factor and will be a sod to get through the conduit boxes!
If you have access at the other end I would start again with at least 6mm even if it's not back to supply at least it's part done!

I also hate RCD main switches, if it trips everything goes off.
I'd separate the lights and sockets onto two circuits.
If like me you use grinders ect in there the last thing you want is the lights to go off half way through some 4inch box!
Sy

 

[RaceDiagnostics]

I suspect when the house was rewired 10 years ago they laid in a new 4mm twin and earth till they got to the tricky part and just joined it to the old cable. I've found plenty examples of bad workmanship.

Anyway I'll lift the floor sometime in the next few days but I think taking 6mm all the way back to the house CU will be tricky.

 

[qwakers]

14mm2 swa? s'what i did and i can be sure ill never take it to the limit

 

[brightspark]

14mm2 swa? s'what i did and i can be sure ill never take it to the limit

never seen 14 mm. normaly goes from 10mm to 16 mm then 25 mm

 

[sparkysy]

^^^^ perhaps it started as 16mm but was a tight pull so stretched and shrank a bit!

 

[qwakers]

might well be 16 mm2, it was 6 years(ish) ago

 

[Barking Mat]

Don't pull the floor up, attach a solid string type thing, pull the old cabling out, and thread the new cabling back through, pulling on the string.

Bet, it's not that simple, but I'd start there.

 

[RaceDiagnostics]

No chance, the run to the CU must be 20m away, going through multiple right angle bends.

 

[dobbslc]

Don't pull the floor up, attach a solid string type thing, pull the old cabling out, and thread the new cabling back through, pulling on the string.

Bet, it's not that simple, but I'd start there.

Problem with doing that is burning the other cables pulling it through, I've seen T&E down to the copper!

 

[RaceDiagnostics]

The first board I lifted turned out to be lighting circuits but the T&E was pinched under the boards in two places.

After lifting a few more boards I found the junction between the new 4mm and the old 2.5mm.

Any suggestions on the best way to get 4 or 6mm into the garage. I bet it will be difficult to thread it though these old conduits. Is there a more modern equivalent?

 

[RWD3M]

The first board I lifted turned out to be lighting circuits but the T&E was pinched under the boards in two places.

View attachment 385158


View attachment 385159


After lifting a few more boards I found the junction between the new 4mm and the old 2.5mm.

View attachment 385160

View attachment 385161


Any suggestions on the best way to get 4 or 6mm into the garage. I bet it will be difficult to thread it though these old conduits. Is there a more modern equivalent?

View attachment 385162

View attachment 385163

Oh dear!

As has been hinted, if you have the access, both in the house and the garage, could you run a fresh SWA (I have 10mm which is good for in excess of 60A) from CU to CU?

 

[RaceDiagnostics]

Unfortunately, getting new cables into the house CU is close to impossible. The CU is just above a wood floorboard floor, which has the had a new solid wood floor running perpendicular to it laid on top. For the wires coming in from below there is a sharp dogleg from the subfloor up to the CU. I think all the wires were laid in then both floors laid on top. So no easy way to lift the boards without doing a lot of visible damage. That means I'm stuck with 4mm from the house CU to the join. It's then a question of 4 or 6 out to the garage.

 

[brightspark]

Unfortunately, getting new cables into the house CU is close to impossible. The CU is just above a wood floorboard floor, which has the had a new solid wood floor running perpendicular to it laid on top. For the wires coming in from below there is a sharp dogleg from the subfloor up to the CU. I think all the wires were laid in then both floors laid on top. So no easy way to lift the boards without doing a lot of visible damage. That means I'm stuck with 4mm from the house CU to the join. It's then a question of 4 or 6 out to the garage.

nothing to gain just use 6.0mm hardly any bigger in size than 4

 

[sparkysy]

@RaceDiagnostics
Gutted, those crushed cables are a fault waiting to happen, and the cable joint was just snit!
Do you need the conduits to get across an opening? I would try and replace it with SWA from a waterproof adaptable box on the side of the house, if accessible. Or from somewhere accessible inside.
If not and need to use the conduit two 6mm with a 2.5mm singles earth will go in a 20mm conduit. I would change the end box where it exits the house for a suitable adaptable box and join the singles there, to a twin and earth and take that as close to the house DB as you can! It will be tight with all the direction changes but should be achievable.

 

[RaceDiagnostics]

Here is a better pic showing the challenge.

 

[brightspark]

drop an armoured cable down the wall and cut a small channel across to garage and bury it

 

[RaceDiagnostics]

drop an armoured cable down the wall and cut a small channel across to garage and bury it

I was thinking that, what sort of radius can they take?

 

[sparkysy]

I'd be tempted to chop that conduit and re-route it straight across the front to the wall with a radius 90 to the lower conduit box on the wall.
Start the pull from that box with your new singles and some lube and a bit of wiggle back and forth it will go.
Or swap it for SWA as @brightspark beat me to that, it was coming under this bit!