Insulation added after second fixing!

[nomadicsoul]

Hi everyone.
I need a little advice please. Several months ago I first fixed and second fixed a timber frame loft conversion ( open plan living area and kitchen) for a friend /client. I haven't signed it off yet as I was waiting to install I new CU for him and for him to fit the kitchen. I fitted a kitchen ring final in 2.5mm, socket radial 2.5mm, 2x 6mm hob/oven supplies, a radial, and 2 lighting circuits in 1mm. And smoke detector.1mm. At the time it was simply kingspan with cables through timbers mostly not touching the insulation I used Reference method 102 for calculations. I have however returned to connect up an electric skylight and noticed that every cavity including the 18 inch floor space has been packed with wool insulation changing the reference method to 103. As we know a ring final should not be installed when using ref meth 103 and the radial 2.5m current carrying capacity will be reduced to 13.5A, the 6mm cables to 23.5A. The walls have been plastered and the tongue and grove flooring down and glued. Does anyone have any suggestions on what I can do to remedy this situation? Many thanks in advance.
Si

 

[ImpededLoop]

All you can do is derate the circuit breakers providing that the connected loads will not then exceed the rating of the circuit breaker.

It sounds like you've put plenty of thought into designing the installation which is great to hear

 

[littlespark]

Derate the breakers….. after producing a back dated test cert to say it was all right when you second fixed.

 

[timhoward]

I feel the pain on this one - lots of thought went in and they stuffed it up (almost literally) for you.
The other problem is that this is a loft conversion, and building regs will have been inspecting it. So this isn't really one to bend the rules too much on.
One creative thought - the merits of which can be critiqued!
If you change the first and last socket on the kitchen ring to a 13A FCU, split the ring in the middle, and feed from two 16A breakers on the basis of downstream overload protection..... then if the loads are neatly divided you get the max 26A of design current out of what is there then.

 

[nomadicsoul]

Tim Howard. I like that idea. Certainly an idea to consider.Thanks very much.

 

[Petej999]

Hi everyone.
I need a little advice please. Several months ago I first fixed and second fixed a timber frame loft conversion ( open plan living area and kitchen) for a friend /client. I haven't signed it off yet as I was waiting to install I new CU for him and for him to fit the kitchen. I fitted a kitchen ring final in 2.5mm, socket radial 2.5mm, 2x 6mm hob/oven supplies, a radial, and 2 lighting circuits in 1mm. And smoke detector.1mm. At the time it was simply kingspan with cables through timbers mostly not touching the insulation I used Reference method 102 for calculations. I have however returned to connect up an electric skylight and noticed that every cavity including the 18 inch floor space has been packed with wool insulation changing the reference method to 103. As we know a ring final should not be installed when using ref meth 103 and the radial 2.5m current carrying capacity will be reduced to 13.5A, the 6mm cables to 23.5A. The walls have been plastered and the tongue and grove flooring down and glued. Does anyone have any suggestions on what I can do to remedy this situation? Many thanks in advance.
Si

Were you aware of work undertaken whilst you were first fixing, if son down to you to sort the problem, I THINK.

 

[Petej999]

Hi everyone.
I need a little advice please. Several months ago I first fixed and second fixed a timber frame loft conversion ( open plan living area and kitchen) for a friend /client. I haven't signed it off yet as I was waiting to install I new CU for him and for him to fit the kitchen. I fitted a kitchen ring final in 2.5mm, socket radial 2.5mm, 2x 6mm hob/oven supplies, a radial, and 2 lighting circuits in 1mm. And smoke detector.1mm. At the time it was simply kingspan with cables through timbers mostly not touching the insulation I used Reference method 102 for calculations. I have however returned to connect up an electric skylight and noticed that every cavity including the 18 inch floor space has been packed with wool insulation changing the reference method to 103. As we know a ring final should not be installed when using ref meth 103 and the radial 2.5m current carrying capacity will be reduced to 13.5A, the 6mm cables to 23.5A. The walls have been plastered and the tongue and grove flooring down and glued. Does anyone have any suggestions on what I can do to remedy this situation? Many thanks in advance.
Si

Advice for what its worth study the entire spec for the building before you start any work.

 

[nomadicsoul]

Were you aware of work undertaken whilst you were first fixing, if son down to you to sort the problem, I THINK.

No i only discovered the insulation by chance. I didnt know it was going in . He added it for sound proofing apparently. But I am trying to sort the issue.

 

[nomadicsoul]

Advice for what its worth study the entire spec for the building before you start any work.

Thanks. We discussed insulation . The home owner added it after my work was done but as hes a friend i feel obliged to sort it.

 

[ipf]

Thanks. We discussed insulation . The home owner added it after my work was done but as hes a friend i feel obliged to sort it.

I'd say he's the one obliged to sort it out. Being a friend, it should be easier to get the point over to him........just how he's cocked your work up and how it needs to be put right. Good luck.

 

[LastManOnline]

Thanks. We discussed insulation . The home owner added it after my work was done but as hes a friend i feel obliged to sort it.

Insulation companies are doing exactly the same in thousands of homes up and down the country. In reality no one is usually around to determine what the effects are on cable insulation. There is no obligation on the insulation company to have any assessment carried out on the potential implications. It's a funny old world

 

[Petej999]

I'd say he's the one obliged to sort it out. Being a friend, it should be easier to get the point over to him........just how he's cocked your work up and how it needs to be put right. Good luck.

As long as they pay you for the work and materials

 

[brianmoooore]

There are hundreds of thousands of properties in the UK where the installation method has gone from surface to fully enclosed in insulation, dating from when the government started offering loft insulation top ups from 4" to 10". Normally only affects immersion heater and electric shower supplies in houses, but, in bungalows, overloads the socket and cooker circuits as well.

 

[pc1966]

If you change the first and last socket on the kitchen ring to a 13A FCU, split the ring in the middle, and feed from two 16A breakers on the basis of downstream overload protection..... then if the loads are neatly divided you get the max 26A of design current out of what is there then.

Simpler just to keep it as an RFC on a 20A RCBO, etc. After all methods 100/102 have 2.5mm as 21A, while method 103 has it at 13.5A so:

Max MCB = 32A RFC * 13.5/21 = 20.6A

That way you get better use of the RFC and don't have to know in advance where it should be split on the basis of loads. My own flat has the RFC on 20A for historical reasons and never had an issue with it in terms of total loading. (I think when it was designed in the 70s the MICC sub-mains had too high a Ze for 30A rewirable fuse so to use 20A instead, and as I have no idea exactly where the cables go I kept the 20A rating just in case it was a hidden method 103 somewhere...)

 

[timhoward]

Simpler just to keep it as an RFC on a 20A RCBO

I was under the impression that the regs required 20amps of ccc for the RFC reg to apply. I'm sure it would be fine in practise.
If it's allowed then your way is obviously simpler and better!

 

[telectrix]

He added it for sound proofing apparently.

gag the kids.

 

[pc1966]

I was under the impression that the regs required 20amps of ccc for the RFC reg to apply. I'm sure it would be fine in practise.
If it's allowed then your way is obviously simpler and better!

The only regulation that I know of specific to the RFC is 433.1.204 which covers the case of the OCPD being above the cable rating, but due to the ring structure with fused sockets along it, that is acceptable.

However, I interpreted that as saying you can use an OCPD of 1.5 times the CCC for such a RFC, not that you must use 30A fuse/32A MCB and not anything less. After all, it shows examples of the same BS1363 accessories on a 20A radial in the appendix.

Now one of the main arguments for the RFC is the greater coverage and application of diversity that comes from having 32A backing a number of sockets, versus the 20A radial (or 16A radial more common in the EU), but I never though it was obligatory.

Without wanting to kick off yet another "RFC versus Radial" argument I would still stick with the RFC as I like both the ability to check end-end via r1,r2,rN readings, and the redundancy in the CPC against a single open (which would not be spotted, unlike an open live on a radial). And here I would feel the 20A versus two radials at 16A (which is actually above 2.5mm CCC under method 103!) gives better diversity of socket use.

Maybe the "20A RFC" should be the topic of another thread!

 

[brianmoooore]

Nothing wrong with a 20A RFC if the estimated load is 20A or less, which essentially boils down to (outside of a kitchen or utility room) as to whether or not portable electric heaters are likely to be used.

 

[timhoward]

Lots of people seem to think a 20A RFC is ok. As suggested I'm creating a new thread for that.

And here I would feel the 20A versus two radials at 16A (which is actually above 2.5mm CCC under method 103!) gives better diversity of socket use.

I agree that if permitted a 20A RFC is much better. I should also clarify that I don't actually like my idea, I was just trying to think of wacky approaches! Whether a good idea or not, I believe you could be in compliance with letter of regs by having a 16A breaker, method 103, and applying the downstream overload protection exemption by either having the first length within 3m or relying on RCD for fault protection. (yuck, yuck, and thrice yuck...)
Then 433.2.2 is met. It is the last think I'd want to do, and future inspectors would have a field day, but occasionally circumstances conspire and the last resort methods come out to play.
Much better for the OP to get the installation sorted out as originally intended of course!