yet another kitchen

[ajrobb]

No one seems to have mentioned RCD protection yet, for the sockets and concealed cables.....

Ah, that would have been another post. However, as this work in the kitchen is probably notifiable, I'll talk to my LABC about also replacing the CU and adding another ring.

I already have the much larger lounge ceiling down, so dropping the 9.5mm plasterboard kitchen ceiling won't be much more of a problem. Then I can really get at the cables.

 

[Taylortwocities]

OK, but are conductors of 1.5mm and 2.5mm diameter common?

It is CROSS SECTIONAL AREA of the conductor, NOT DIAMETER.

Find the radius and use Pii r²

 

[ColJack]

. .

blimey, first time I've seen BAS rendered speechless.. good one ajrobb

 

[ajrobb]

It is CROSS SECTIONAL AREA of the conductor, NOT DIAMETER.

Yes, that's what I assumed, but was told off for assuming.

As far as Ze calcs, the proposed extension is MUCH shorter than the old run from switch to immersion heater. As long as I keep to at least the original cable size, I don't see a problem. Anyway, I'll see what LABC says.

 

[ajrobb]

I guess that current regulations make it difficult to offer firm advice. It is interesting but frustrating that nobody offered to say what Iz is for two cables with twin 1.5mm² conductors running through oval conduit in plaster.

OK, I didn't ask that explicitly but there must be miles of this stuff installed every day.

 

[Taylortwocities]

But the information on current carrying capabilities (Iz) of cables is available, in detail, in BS7671. Ther is a shorter version in the OSG.
Iz will depend on a number of factors, including the reference method employed.

And by the way, it is not good asking LABC for advice and guidance on this.
They will expect to come to site and see that you have installed, tested and certified that the works comply with Building Regulations and (by extension) BS7671..

If you haven't and/or it doesn't they will kick you into touch.

 

[LoveRocket]

They will expect to come to site and see that you have installed, tested and certified that the works comply with Building Regulations and (by extension) BS7671..

If you haven't and/or it doesn't they will kick you into touch.

Even though that isn't how it's meant to work, and THEY should do the I&T at THEIR expense if you've notified and paid the fee.

 

[LoveRocket]

if the sockets will be inaccessible then they require isolation points in an accessible location.

No they do not.

explain.

Nowhere in BS7671 does it state that kitchen appliances supplied from under-counter sockets must have an isolation switch above the worktop.

 

[ajrobb]

Even though that isn't how it's meant to work, and THEY should do the I&T at THEIR expense if you've notified and paid the fee.

That sounds more hopeful, thanks. I think I read that only a BC can certify other people's work. A spark can only certify his own.

 

[ban-all-sheds]

. .

blimey, first time I've seen BAS rendered speechless.. good one ajrobb

Not really speechless - I made a post which, by the time I clicked Submit, had been rendered superfluous by ajrobb's post immediately before it. I was on the verge of going out and so only had time to delete the text, not replace it....

For a twin-core 1.5mm² sheathed cable running under galvanised capping in the plaster, the Iz looks like it will be somewhere around the 15A present fuse rating.

That would be Reference Method 3, which gives a capacity for 1.5mm² of 20A.

But as you've got BS 3036 fuses, you need to adjust that by a factor of 0.725, so it's capacity becomes 14.5A, which is less than 15. Not a lot, but less is less.

Or, turned on its head, for a 15A BS 3036 you need a cable with a rating of 15/0.725, i.e. 20.68A, which is more than 20. Not a lot, but more is more.

Given that you're going to have to find a way to add RCD protection, go with the idea of replacing the CU, do away with the rewirable fuses, stick with 2.5mm² for 32A ring finals or 20/25A radials.

 

[securespark]

Not a lot

Not a lot

Now the mystery of Ban is revealed. He's Paul Daniels!

 

[ajrobb]

That would be Reference Method 3, which gives a capacity for 1.5mm² of 20A.

But as you've got BS 3036 fuses, you need to adjust that by a factor of 0.725, so it's capacity becomes 14.5A, which is less than 15. Not a lot, but less is less.

Thanks BAS, it looks like the existing wiring/CU would not meet current regulations but is probably not exactly dangerous.

With a new CU, what rating factor should I use instead of the 0.725 for the old semi-enclosed fuses?

Untitled

• ajrobb
• 25 Apr 2010
• 2

The top fuse-box has 5 of the 6 fuses used (none, lighting, lighting, immersion, sockets, cooker). The bottom fuse box is not connected. (I took the fuse covers off for the pictures.)

Should I use conduit or just clip the new cable into the channels and plaster over it?

If I put in a new ring in twin-core 2.5mm² running in plaster and a new CU, what rating would that have and what circuit breaker should I use, please? I'm planning 5 twin-socket outlets. Do I need to run a separate earth?

 

[ban-all-sheds]

With a new CU, what rating factor should I use instead of the 0.725 for the old semi-enclosed fuses?

1.

Or in other words there isn't one.

The reason for the adjustment with that type of device is their extreme reluctance to do their job properly. Those "15A" fuses of yours will actually let 27A through indefinitely, and possibly 30A for an hour. The 30A one will pass 54A indefinitely and up to 60A for an hour and 15 minutes.

Should I use conduit or just clip the new cable into the channels and plaster over it?

Conduit can be useful if you ever need to make changes (e.g. replacing a twin & earth switch drop with 3-core & earth for 2-way switching or to replace a 1-gang switch with a 2-gang. Or if you want to add more sockets so need to get at the cable running between 2 existing ones.

Using steel conduit on lighting circuits means that you don't need to put them on an RCD.

If I put in a new ring in twin-core 2.5mm² running in plaster and a new CU, what rating would that have and what circuit breaker should I use, please?

27A and 32A.

You really ought to spend some time studying....

I'm planning 5 twin-socket outlets. Do I need to run a separate earth?

Why should you?

• //www.diynot.com/wiki/electrics
  
  
• //www.diynot.com/forums/viewtopic.php?p=75416#75416
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/electricity.html
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/domesticinstallations.html
  
  
• //www.diynot.com/forums/viewtopic.php?t=7553
  
  

 

[ajrobb]

I took out the kitchen sink today and found a wire sticking out of the wall not connected. I pulled it and it came out the plaster where it wandered up to the ceiling. It is the earth from the mains that was disconnected by the kitchen fitters in 1993.

I'm thinking of re-plumbing in plastic but the gas to the new boiler will be in copper. What should I do with this green wire?

 

[ban-all-sheds]

//www.diynot.com/wiki/electrics:earthing_supply_types_and_bonding

And from here pick one of the first four, and the next three.