Underground T&E?

If this is a domestic set-up then I can't see there being that many existing cables in the duct so if you are concerned then if it is not too much trouble disconnect and pull the old ones out and draw them all back in together.
Yes, that would be an answer. Indeed, if BAS (well, really the regs!) were to have his way, I'd be pulling out those 'signal' cables and replacing them with ones which had Band II rated insulation, anyway - but I don't intend to comment on whether or not I'd do that :-)

Kind Regards, John.
 
What size SWA are you looking to pull through? 100mm is a fairly generous diameter as far as the ducting goes, so unless you already have a lot of cables in there, I can't foresee a problem. Apply lubricant liberally, of course.

It would only be very modest sized SWA, but size it not the issue (it's a big duct with not much in it). Have you not experienced the problem when pull cords/tapes have got wrpped around existing cables? The additional flexibility of T&E might then be an advantage. However, as ricicle has just suggested, one solution would be to pull out the existsing cables and then pull them back in with the SWA.

If you pulled through a new cord at the same time as your signal wires, I can't really see how this could have happened. It's generally more of a problem if subsequent cables are fed through a duct/conduit with a semi-rigid snake or draw tape, when they will simply take the route of least resistance. Even if there are a few twists, I can't see it being an issue with cable lubricant applied and in a lightly loaded duct.
 
Pull the ELV cables out, using them to pull in a draw cord at the same time.

Gaffer-tape* flexible conduit to the SWA, and put the signal cables into that.

Pull the whole assembly into the duct.


* No, it's not permanent, but I'm assuming that it won't matter that the glue will dry up and the tape will fall off at some time in the future.

If the duct has smooth walls you could use cable ties instead of tape.
 
If you pulled through a new cord at the same time as your signal wires, I can't really see how this could have happened.
One probably wouldn't think so, but I've certainly suffered from this is the past. Don't forget that these cables I'm talking about are very small, so can easily twist (with the cord twisting around some of them them) - and one has then potentially set the scene for deep trouble (short of pulling out all the cables and starting again with a duct which is empty other than for a 'clean' cord.

Anyway, we'll probably get to see - and I hope you're right!

Kind Regards, John.
 
Pull the ELV cables out, using them to pull in a draw cord at the same time.
Gaffer-tape* flexible conduit to the SWA, and put the signal cables into that.
Pull the whole assembly into the duct.
Yes, that would be a viable plan.
If the duct has smooth walls you could use cable ties instead of tape.
It has got smooth walls, but I don't think I'd chance my luck with cable ties. I imagine that the flexible conduit would only need to be attached to the SWA at the leading end, wouldn't it?

Kind REgards, John.
 
Just for the record, I previously wrote:
Furthermore, although you are undoubtedly right that the current signal cables are not rated at Band II voltage levels, I'd be pretty surprised if, in reality, their insulation can't stand 230V (I think you may have moved me to conduct an experiment!).
I have now conducted some quick experiments, on 4-core and 8-core 'alarm cable', rated at 60V. Both have 7/0.2mm conductors (csa about 0.03mm), 0.2mm PVC insulation and 0.2mm PVC sheathing.

A full 100m reel of the 4-core cable gives IR measurements at 250V, 500V or 1000V which are 'off the scale' (>200MΩ, >500MΩ and >1000MΩ respectively). The same results were obtained with a a part reel of about 50m of the 8-core.

I then submerged all but the ends of a 20m length of the 8-core cable in a strong salt solution, with a bit of copper pipe in the solution as an electrode. IR measured between the conductors (all connected together) and the electrode in the salt solution was again 'off the scale' at 250V, 500V and 1000V. That was not changed after an hour or so of immersion. I'm now going to leave the cable submerged for a few days and then test again.

These results don't surprise me. I can but wonder what it is that causes the cables to be 'rated' only at 60V - is it perhaps an essentially arbitrary matter of the thickness (or lack of it!) of the insulation and sheathing?

Kind Regards, John.
 
There is little need to rate alarm cables higher than 60v as they only run at about 12v. Another chain of thought, how do they react to 60v> AC?

If you class your earthed SWA armour as screen (size depending) then I don't see a massive issue with them in the same duct.

edit, added (size depending)
 
JohnW2 - I do think this discussion (and several of your previous posts) has now gone beyond a DIY forum and you should take up your discussion with the authors of the red book and/or the IET.

As the red book says the regulations are non-statutory..but may be used in a court of law in evidence to claim compliance with a statutory requirement.

It also says that there may be other ways to achieve the objective of a specific regulation. If you feel that your underground cable proposal meets or achieves the relevant regulations then carry on. If anything goes wrong - (electricuted horses etc) then you can cite the relevant regs in court.

I just don't want you to start taking the IR reading of boiled cabbage at 1000v dc. :wink:
 
JohnW2 - I do think this discussion (and several of your previous posts) has now gone beyond a DIY forum and you should take up your discussion with the authors of the red book and/or the IET. .... the red book says the regulations are non-statutory...also says that there may be other ways to achieve the objective of a specific regulation.
Whilst I could easily understand your saying that in relation to a good few other threads/posts of mine, I'm a little surprised that you say it in relation to this one - at least in terms of the main issue (the use of T&E underground). Even though, as you say, it would be an acceptable approach, I have not been suggesting a way of achieving the objective of a regulation by a means different from that actually specified in the regs. Rather, I have merely been talking about the invocation of the fact that 522.8.10 of BS7671 actually says, explicitly, that armour is not required if a cable is "installed in a conduit or duct which provides equivalent protection against mechanical damage". Hence, if one believes that the installation provides that degree of protection against mechanical damage, then using that approach would be compliant with the explicit words of the regulation, not an 'alternative means of achieving the reg's objective'. That's how I see it, anyway, and I'm not sure I can think of any sensible interpretation of 'equivalent protection' which would not be satisfied by several inches of concrete!

The SELV cable business is a separate issue. I do think the regulations are silly, and perhaps should not be discussing that here - but I have, in any event, already indicated that I would probably play along with the regs, just so that I could say that what I had was completely compliant - which is, of course, what everyone, including DIYer readers theoretically should do.

I just don't want you to start taking the IR reading of boiled cabbage at 1000v dc. :wink:
I don't need to do that. I already know that the 'IR' would pretty low if it were still wet and well seasoned!

Kind Regards, John.
 
There is little need to rate alarm cables higher than 60v as they only run at about 12v.
That's obviously very true, and I suppsoe it makes production easier and cheaper if they only have to test to 60V - but for reasons such as we're discussing, it can be a bit of a nuisance for users if the insulation is really up to much more than that voltage.

Another chain of thought, how do they react to 60v> AC?
Good question; watch this space.

If you class your earthed SWA armour as screen (size depending) then I don't see a massive issue with them in the same duct.
As you know, I haven't ever seen an issue at all, let alone a massive one, but the question relates to what would be needed to comply with regulations. Are you saying that you think that earthed SWA armour would satisfy the regs?

As I sit and type this, I'm far from convinced that the cable I'm looking at carrying 19V DC out of my laptop's PSU will be rated for 230V, so does that mean that I should take steps to make sure that it does not come into contact with the mains cable feeding it? :-) ... or is it OK because it's not 'fixed? :wink:

Kind Regards, John.
 
iirc you can run band 1 and band 2 in close proximity if the band 2 cable is screened, the screen needing to be at least the CCC of the live conductors in the cable.
You'll have to check the regs as I don't have them to hand though!
 
iirc you can run band 1 and band 2 in close proximity if the band 2 cable is screened, the screen needing to be at least the CCC of the live conductors in the cable.
You'll have to check the regs as I don't have them to hand though!
Thanks. I'll try to resist the temptation to say any more about 'silly' :-) Even once one has taken the armour material (steel) into account, I would think that smallish-sized SWAs would more than satisfy that requirement, wouldn't they?

Kind Regards, John.
 
If you do the math and convert the armour to copper equivalents for the CSA then you'll more than likely find they will be a fair bit bigger equivalent CSA than the live conductors hence I'd imagine will be fine.
 
If you do the math and convert the armour to copper equivalents for the CSA then you'll more than likely find they will be a fair bit bigger equivalent CSA than the live conductors hence I'd imagine will be fine.
Indeed; that's what I was suggesting. I'll do the sums later to be sure.

Kind Regards, John.
 

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Back
Top