feed to DB has earth through a seperate bush to L&N????????

[apprentice87]

Hi Wozz,

Yes, you can get aluminium armored, which so far as i know would prevent "circulating currents" but you would still have the problem of it going into enclosures. Might have been DC circuits perhaps??

Hi Badger,

"but yet the dno are allowed to use concentric cable which effectively creates a single core armoued type cable, although it has the neutral on the outer cores/sheath if pme'd or tncs then the outer sheth part is at earth potential / neutral potential anyway, so therefore no difference in single core armoured"

The concentric stuff might have a single "core" if you like, but it is still TWO conductors grouped together. In a single phase one, the current runs down the middle, and back up the surrounding "concentric" bit, so it is still a pair of conductors "in action" if you like as a pair, which is the important bit in avoiding undesirable electromagnetic effects. In an "ordinary" single core SWA cable, [unlike the DNO service cables] presumably the concentric armour does not carry any current under "normal" fault free conditions, so it is just one conductor "on its own" as it were.

In a three phase concentric service cable, the outer concentric bit may or may not carry and load depending on phase balance, but the other conductors are still all grouped together and in action at the same time.

If the three phase service cable feeds a load on just one phase, then the concentric neutral will then start carrying current, and we are back to a pair of conductors running together!!

john..

 

[philbas]

I stick with my earielr post. If we have to worry about the effects of heating because we have enough current in the cpc to provide it we have a MUCH bigger problem elsewhere

 

[wozz]

Nope AC submain, 300m armoured singles, definitely used ali gland plates as they were a nightmare to drill.

 

[Sidewinder]

wozz,

If Ali gland plates then no issues.

Mind why was the Ali so much of an issue to drill?

 

[steptoe]

of course the cpc enters the c/u, as its the third core ie the LIVE NEUTRAL AND CPC inside the main part of the SWA

3ph N , but I dont install much 5c SWA myself :|

Im still to be convinced that the CPC entering a metal enclosure is in fact happening, and its not actually an integral part of said enclosure.

 

[james KEI]

here is a picture i took on my phone at the time so may not be great quality

you can see the submain cpc enters in the left bush and the L+N in the right bush (from the meter)

---------- Post Auto-Merged at 20:10 ---------- Previous post was made at 20:01 ----------

in my opinion although the trunking is connected to earth we're not relying on it for the cpc or we'd have no seperate cpc like in old conduit, they used the conduit for earth and so it only contained L+N and a fly lead off the box/accessory(if that).

we do have a seperate cpc here (the db is relying on this for its earth, not the trunking) and so it should be run through the same hole as the L+N

interesting read and to see difference in opinion. Thanks all and especally apprenctice87

 

[steptoe]

that unit plastic?

---------- Post Auto-Merged at 20:28 ---------- Previous post was made at 20:26 ----------

thats a totally different issue then,

and I would have to concede my learned colleagues are right about the same hole, as the conductors are leaving the metal enclosure.

 

[Zeespark]

It looks to be plastic Steps.

AndyGuinness

 

[apprentice87]

Hi Steps,

What you think?? So far as i can see, all they got to do is to pull out the CPC from the hole on the left [that presumably wends its happy way to the MET] and then stuff it through the same hole as the tails from the meter, and all will be just lovely!!

john..

 

[Manator]

There is really no need

 

[steptoe]

I agree with Manator,

maybe not the best practice, but it really wouldnt bother me in the slightest,

my reference to the same hole would be in line with the word of the regs,

but, hey ho, BGB says its OK so no worries,

and, I have done similar myself loads of times,

just have a look at the pic I put on matt.leung 's isolation thread,

 

[Nicky Tesla]

it doesnot matter if the db is plastic or not. The metal trunking if ferrous, and that is where the heating effect would be, IF there was a problem. But there isn't

 

[Sidewinder]

There is, it did not comply with the brb.

It now seems to comply with the bgb so those working to that can now on PIR's not comment upon this.

 

[steptoe]

it doesnot matter if the db is plastic or not. The metal trunking if ferrous, and that is where the heating effect would be, IF there was a problem. But there isn't

its not about heating Nicky, and the fact the cu is plastic would change my stance on whether or not it complied to the letter of the regs 2008,

either way, I wouldnt even give it a 2nd glance, as Ive said, Ive done it loads of times, as have most of us probably using (someone elses suggestion) parallel earth with SWA scenario.

 

[Nicky Tesla]

eddy currents is what it is about, which causes the heating effect,,,,,,an enclosure doesnot have to be a db, the trunking is the enclosure. The cables going in or coming out doesnot matter.

+i dont read it in the BRB as that it doesnot comply, i think they have just reworded it in the green