Would you extend this RFC?

[WD Sparky]

What flooring will you have to remove?

It’s the large sheets of tongue and grove chipboard. I’ll have to cut a channel out across the whole width of the house which spans two bedrooms to be able to drill the joists. They are kids bedrooms too packed full of stuff.
I am considering running it in 4mm SWA around the perimeter of the house as there is a gravel soak away so no digging required.
More expensive material but much less hassle.

 

[Midwest]

It’s the large sheets of tongue and grove chipboard. I’ll have to cut a channel out across the whole width of the house which spans two bedrooms to be able to drill the joists. They are kids bedrooms too packed full of stuff.
I am considering running it in 4mm SWA around the perimeter of the house as there is a gravel soak away so no digging required.
More expensive material but much less hassle.

Then you’d cause more damage to the structural floor, than an inconvenience to continuity of service.

If the figures hold out, I’d alter the RFC. Would the final Zs be ok, if you did so?

 

[Pete999]

It’s the large sheets of tongue and grove chipboard. I’ll have to cut a channel out across the whole width of the house which spans two bedrooms to be able to drill the joists. They are kids bedrooms too packed full of stuff.
I am considering running it in 4mm SWA around the perimeter of the house as there is a gravel soak away so no digging required.
More expensive material but much less hassle.

Not an ideal method, is surface wiring a no no? PVC trunking.

 

[Pretty Mouth]

I have the current volt drop calculation as Vd = L x Ib x (mV/A/M)/ 4 x 1000.
So VD = 113 x 32 x 18 /4000 = 16v
5% of 230V = 11.5, so its already over the allowable 5%

The max length for RFCs of 106m uses a design current of 26A (there's a table earlier in the chapter in the OSG that should state this), distributed evenly around the ring. I presume multiple calculations were used to arrive at the 106m figure.

 

[davesparks]

I'd extend the ring personally as long as the Zs is going to be within limits.
The onsite guide with its pictures and tables is just a guide, not a requirement. The point of the
The volt drop won't be a problem as the actual load is going to be less than the 32A you've used to calculate it.

 

[Wilko]

Hi - as per Dave.
If the extension has heating that doesn’t rely on this circuit likely the biggest new load will be a vacuum cleaner .

 

[ruston]

I agree too as as long as your ZS is within the the limits of the installation methods .
If I remember correctly 100mtr square was the limit of an RFC without calculation.

 

[Risteard]

The cable length calculation I used was

Vd = L x Ib x (mV/A/M)/ 4 x 1000.
So VD = 113 x 32 x 18 /4000 = 16v

I’ve already divided the end to end value by 4. This is how I was taught to calculate volt drop at the mid point on a RFC.

Does this look correct to you?

I wouldn't use 32A as the design current.

 

[stevethesparks]

if your r1 & rn are 0.84 I would hope to see the r2 at around 1.4

 

[DefyG]

De-rate it to 20A RFC if possible, VD would be less than 5% if using the full 20A load but as the main usage would be the kitchen RFC I doubt the remainder would use 20A (unless electric heating!). Higher max Zs value too!