Aluminium CPC

[ringer]

I recall seeing in a DB the other day a 4mm aluminium CPC with 6mm copper line conductors (singles). In the OSG section on 'Earthing conductor and main protective bonding conductor cross-sectional areas' there is a footnote to the table (p28 red OSG, p40 green OSG) saying...

'Protective conductors (including earthing and bonding conductors) of 10mm csa or less should be copper'

This, to me, implies that ALL protective conductors <10mm should be copper.
Is this correct, and therefore the 4mm cpc mentioned above does not comply?

The circuit involved (radial for one double socket just below the DB) did very much strike me as being cobbled together with whatever the 'installer' had to hand at the time.

 

[Silly Sausage]

I recall seeing in a DB the other day a 4mm aluminium CPC with 6mm copper line conductors (singles). In the OSG section on 'Earthing conductor and main protective bonding conductor cross-sectional areas' there is a footnote to the table (p28 red OSG, p40 green OSG) saying...

'Protective conductors (including earthing and bonding conductors) of 10mm csa or less should be copper'

This, to me, implies that ALL protective conductors <10mm should be copper.
Is this correct, and therefore the 4mm cpc mentioned above does not comply?

I would read that as a 'Yes', it should be copper.

 

[oxocube]

And for cables 16mm and smaller the cpc should be the same size or the copper equivalent.

 

[ringer]

And for cables 16mm and smaller the cpc should be the same size or the copper equivalent.

How does that work with T&E then? This case is singles, but am interested to know for future reference.

PS can you not use the adiabatic to justify smaller cpc?

 

[oxocube]

Ha ha, I can't answer that either, the regs say cpc is sized by adiabatic equation or from table 54.7 no other options, which means T&E does not comply with the regs.

I did'nt want to hijack so started a new post, have a look at my post 'cpc sizing',

 

[Engineer54]

I recall seeing in a DB the other day a 4mm aluminium CPC with 6mm copper line conductors (singles). In the OSG section on 'Earthing conductor and main protective bonding conductor cross-sectional areas' there is a footnote to the table (p28 red OSG, p40 green OSG) saying...

'Protective conductors (including earthing and bonding conductors) of 10mm csa or less should be copper'

This, to me, implies that ALL protective conductors <10mm should be copper.
Is this correct, and therefore the 4mm cpc mentioned above does not comply?

The circuit involved (radial for one double socket just below the DB) did very much strike me as being cobbled together with whatever the 'installer' had to hand at the time.

I take it this is an older installation, and if so it will comply with previous Reg's of that time. As it's such a short run, i'd leave well alone, unless the customer wants it rewired that is....

 

[ringer]

It is an older installation (1990) but this particular circuit is a very recent addition. The run is extremely short as well so replacement no real problem. Just didn't want to replace if not necessary. Am revisiting site for another job next week so may just replace it anyway. Only have 10mm and 4mm g/y to hand though. Don't fancy buying a roll of 6mm just for this, especially as it will just be done as a favour. Plan to replace lines 2.5mm and cpc 4mm, all of which I do have to hand.

 

[Richard Burns]

Are you sure it was not a tinned copper CPC?
If you are replacing just the CPC then check using the adiabatic if 4mm is OK; it should be if it is a radial only feeding a single double socket, but probably better to replace all of them if the customer is happy with that.

 

[ringer]

Tinned copper? How would I check for that, apart from cutting in to the cable? Can I just scrape at an exposed strand? Does the tin comes off easily. Must admit I am just assuming it is Al because it looks like Al.

 

[Richard Burns]

This was just one thing with which I was caught out recently! The aluminium wire bends slightly differently than copper as it is softer, but this is difficult to tell. If the wire is in screw terminals you may be able to see the copper where the screw has scuffed it, or you can take a knife and pare off the surface at the end and look for copper colour (the tinning bonds well, so you are just looking for a hint of copper).
Might save you having to rewire!

 

[Chr!s]

Tinned copper? How would I check for that, apart from cutting in to the cable? Can I just scrape at an exposed strand? Does the tin comes off easily. Must admit I am just assuming it is Al because it looks like Al.

Just expose a joint, normally you will see the copper showing through. Is it old wiring, aluminium was used in the 70's for a short period of time, this might give you a bit of a clue. The issue was with terminations, creep, galvanic corrosion and oxidation. You could check the temperature of the terminations to ensure permitted temps are not being exceeded. The cable is otherwise as effective as copper pretty much and has a good longevity.

Regards Chris

 

[telectrix]

Tinned copper? How would I check for that, apart from cutting in to the cable? Can I just scrape at an exposed strand? Does the tin comes off easily. Must admit I am just assuming it is Al because it looks like Al.

get a pikey to come round. they can smell copper at 50 paces.