Underfloor Heating

[hmltnangel]

Hi folks,

Just after a wee bit of help.

Finished laying my heating etc and about to get the bits required for my electrician friend to do the final wiring to the mains. Need to get the bits for him so that its a ten minute job to check my wiring (which is good, I am a relatively competent DIY'er)

What do I need.

Heating system is rated max 16A with the elements I have totalling a shade under 12A. It recommends a 30 mA RCD for connecting to the mains.

This is my fusebox under the stairs, any pointers to exactly what I need? You can see the 1.5 mm cable I have ran to just beside the fusebox, so it literally is just the final connection now.

 

[riveralt]

I hope you have checked your insulation resistance reading corresponds to that described in the instructions.
Are you sure the instructions say use 1mm ² T&E - last one I did required min of 1.5mm ² T&E.
What are the controller instructions saying regarding cable sizes?
What size MCB are you required to fit?
There doesn't look like there is any space on the bottom CU with RCD.
Don't you not think you should be talking to your 'electrician' friend regarding these requirements. After all he may not agree with our recommendations and since he will signing the new circuit off I would think he would want to have a say in how you install this product.

 

[bernardgreen]

a ten minute job to check my wiring (which is good, I am a relatively competent DIY'er)

What is the maximum safe current that 1 mm cable can carry. ? You might just get away with 1 mm at 12 amps

Check it out here

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

, any pointers to exactly what I need?

An electrician and maybe the courage to have the work re-done with the correct size of cable.

 

[hmltnangel]

I had checked it on there, which is why I know I could have went with 1mm. Its in an internal non isulated plasterboard wall.

Actually the mistake I made is not putting 1.5mm in my post above (now edited) It is actually 1.5mm I installed it with. (Hanging head in shame for schoolboy typo error)

The cable runs approx 2.5m from the thermostat, inside the plasterboard wall, then back out at the fusebox.

So I only need to know what to buy for it to be fitted at the fusebox.

30mA RCD - as you say theres no space inside the box that already has one

The top box however, has had all the storage heaters removed from teh circuits. Would I be right in saying that this box can be used? Or am I better just buying a new Consumer Unit with RCD/MCB in place then having it wired in that way?

 

[PrenticeBoyofDerry]

As you have space in the unit that is used/no-longer used for heating, the best option would be to fit a RCBO that is type tested for the board. I believe the product code number would be "ADN116".
But the best advice would be to confirm this and have the rest of the installation characteristic, cable selection, routing and conformity to the manufacturers instructions checked out by the electrician you have agreed to complete the commissioning of this work.

 

[securespark]

1 milli clipped direct is 14A.

1 milli would do OK for 12A @ 12m length @ 30 degrees and 100mm of insulation.

EDIT. More than that 1.5 is OK, but seeing as that is what you have anyhow....

 

[PrenticeBoyofDerry]

Thought flat T&E was 16A clipped direct?
Table 4D5

 

[securespark]

I made a typo. But I still don't make it 16. Rightly or wrongly, I use 15A, ie don't use 4D5.

Are the cables referred to in 4D5 to BS 6004?

 

[PrenticeBoyofDerry]

Are the cables referred to in 4D5 to BS 6004?

I believe so.
http://www.eland.co.uk/documents/624-Y_Twin_and_Earth.pdf

 

[PrenticeBoyofDerry]

unless there is another 70 degree C (PVC) insulated, sheathed flat cable with copper CPC on the market?

 

[securespark]

So, just to get this right, you're telling me I have been using the wrong table for T&E my entire professional life if I have not been using 4D5?

 

[RF Lighting]

From what I can see, table 4D5 was introduced with the 17th edition.

In my 16th edition regs, I have T&E written at the side of table 4D2A

 

[EFLImpudence]

1.5mm² is the minimum allowed for a power circuit. Table 52.3.

 

[JohnW2]

From what I can see, table 4D5 was introduced with the 17th edition.

Per the material which BAS sometimes links to, I think that 4D5 was probably introduced due to (very conveniently discovered!!) new information (about CCC) which would make a ring final compliant with Installation Method A (which it wouldn't be per 4D2A)

I personally think the resultant situation is a bit naughty, since there is nothing in or around 4D2A which says that it doesn't apply to T+E, so one ends up with some situations (like the one mentioned above) in which two tables give different CCCs for the same cable with the same installation method.

Kind Regards, John

 

[securespark]

From what I can see, table 4D5 was introduced with the 17th edition.

In my 16th edition regs, I have T&E written at the side of table 4D2A

I have 4D2A in my very first 16th Ed., from 1991.

Before that 9D2 from the 15th Ed. Still rated at 15A.

The 14th was slightly tricky as the cable was imperial. I hope my conversions are accurate.

Table 3 lists 1/ .044 (0.97mm²) at 12A clipped direct and 3/.029 (1.29mm²) at 15A clipped direct.

But then I had my Eureka Moment!

Leafing through my later 16th Ed.s, I found in the brown copy a table titled

"4D5A", which seemed at first glance to be the same as the current 4D5.

So it seems that 4D5 did precede the 17th Edition!!

I personally think the resultant situation is a bit naughty, since there is nothing in or around 4D2A which says that it doesn't apply to T+E, so one ends up with some situations (like the one mentioned above) in which two tables give different CCCs for the same cable with the same installation method.

Quite!