Power to remote garage - conduit and cable and feasibility

[Taylortwocities]

Stevos,

Am a bit concerned about the implications of your last post (if you will excuse the pun). You mention T&E and then ask

I'm still wondering what sort of cable would go through it (in terms of capacity and type), and whether it's worth running two lengths of duct whilst I have the trench dug to future proof it, or whether that would be overkill.

The duct you would install is only to provide an easy way for the cable to be pulled in after the groundworks are done. The duct provides NO additional protection for the cable that will be pulled in. The cable TYPE that will need to go in there is Steel Wired Armoured Cable.

The size of the cable will be determined by the designer (your electrician). He will also determine what needs to go at the far end - this is where the type of earth at the origin (and other considerations) come into play.

There is no reason for you to lay a second duct, unless you also want to run other services (ie telephone/data). Because of wiring regs, and the problem of interference, these should not share the same duct as the power cable.

 

[JohnW2]

Am a bit concerned about the implications of your last post (if you will excuse the pun). You mention T&E and then ask ... The duct you would install is only to provide an easy way for the cable to be pulled in after the groundworks are done. The duct provides NO additional protection for the cable that will be pulled in. The cable TYPE that will need to go in there is Steel Wired Armoured Cable.

I'm not sure what the OP meant by 'type', but the impression I got was that he only mentioned 10mm² T&E as an indicator of the stiffest cable he had personally encountered. The entire thread, right from the OP, seems to have been about SWA, so I had assumed that the OP understood that this would be required (even with ducting).

Kind Regards, John

 

[Stevos]

In terms of the cable choice, that will (when I get round to getting it done) be up to the installing electrician - I have no plans to install that myself.

The T&E comparison was purely intended to get an idea of cable sizes and stiffness, to try to understand what sort of cable will be likely to fit in the duct. SWA would presumably be less flexible than the equivalent capacity T&E.

I have read various opinions about both T&E in a duct, and SWA, and various other cable types, and there doesn't seem to be broad consensus about which / what is appropriate - I've so far been unable to find definitive info about the regs on this (other than reference to "equivalent mechanical protection"). As I haven't handled SWA I can't personally be sure how it would compare in protection to the twin-wall duct I have.

I want this to be done in the most robust and safe way, whilst providing the capacity I need now, and in the reasonably forseeable future, and if I were in a position to decide on cable type, from what I've read I would probably select 3 core SWA, however I'm not sure on the size / capacity / possibility of running SWA through a duct.

Some people I've read have implied that SWA is an *alternative* to running a duct, and that it would be impractical to run it in a duct ( ? )

If running SWA through a 40mm (32mm internal) duct would mean having to choose a thinner lower capacity cable, then I was speculating if running parallel ducts would be useful to allow different conductors to be run in different ducts - using 2 core SWA or something.

 

[ban-all-sheds]

Well I've opted for the 40mm (32mm internal) duct, and plan to try to make the trenches and lay it this weekend.

1. Keep the bends as gently swept as possible, accepting that that will mean stretches of it at each end which will not be at full depth.
   
2. Before you bury it replace the supplied drawstring with some more substantial lightweight rope.
   
3. Remember what was said about photographing the trench with depth indicators, when partially backfilled showing the warning tape, etc.
   
4. To improve the appearance, particularly on the house wall, look for some PVC drainpipe with a 40mm+a bit internal diameter, and slide a length over the ducting to run from where the cable leaves the house to just below ground level. At the top you can use either an elbow to take it through the wall, or put a small enclosure on the wall with the pipe&duct going in through the base. A reducing coupler with the large end inside the enclosure, sitting on a bead of silicone, is an effective way to bring the pipe in, and such an enclosure can be used to join the SWA to the indoor cable.

 

[JohnW2]

I have read various opinions about both T&E in a duct, and SWA, and various other cable types, and there doesn't seem to be broad consensus about which / what is appropriate - I've so far been unable to find definitive info about the regs on this (other than reference to "equivalent mechanical protection"). ... Some people I've read have implied that SWA is an *alternative* to running a duct, and that it would be impractical to run it in a duct ( ? )

'Non-protected' cables (such as T+E) in a plastic duct is not an alternative to the use of SWA (or other 'protected' cables). No ordinary type of plastic ducting will afford adequate mechanical protection to cables such as T+E - you would need galvanised conduit or similar to achieve an acceptable degree of mechanical protection. The idea of SWA is not really that the armour provides much mechanical protection - hit it hard with a spade (let alone some powered tool) and you'll still damage it (quite possibly penetrate it) and need to replace or repair it. The main point is that the earthed armour will result in a protective device (MCB, fuse, RCD) operating if something like a spade does penetrate it.

... if I were in a position to decide on cable type, from what I've read I would probably select 3 core SWA, however I'm not sure on the size / capacity / possibility of running SWA through a duct.

That is very probably what your electrician will advise. If, as you go on to imply, you are uncertain of the size of duct that would be required to facilitate easy drawing through of whatever cable the electrician specifies, you really ought to be talking now to the electrician about the choice of cable (type and) size, and hence also the required duct size.

Kind Regards, John

 

[Stevos]

Thanks - the difficulty is that I don't plan to get the electrical work done now (only that I need to get the ducting done now before I do the decking and patio work), and am not in a position to get a quote / formal advice yet. The cabling work may not be for another 12+ months. depending on when I can afford it and have the time.

Has anyone got experience of SWA sizes compared to ducting sizes? Or are there any tables for this anywhere?

Similarly for other possible options. HiTuff?

 

[JohnW2]

Thanks - the difficulty is that I don't plan to get the electrical work done now (only that I need to get the ducting done now before I do the decking and patio work), and am not in a position to get a quote / formal advice yet. The cabling work may not be for another 12+ months. depending on when I can afford it and have the time.

I wouldn't have thought that there was any reason why you couldn't get quotes (which implicitly require 'advice') now, at no cost, even if the work may be 12 months or so down the road.

Has anyone got experience of SWA sizes compared to ducting sizes? Or are there any tables for this anywhere?

It's not just a matter of sizes - the diameters of SWA cables are freely available (most people who sell them will indicate the diameter). It's more a question of how easy it is to pull the cables through ducts of various sizes (adequate to accommodate the cable!) and lengths, and only those with appreciable experience of doing it will know the answer to that. One approach, of course, is simply to go for 'overkill' in terms of duct size (it can't be too large) and to keep curves/bends to the minimum (large radius only).

Kind Regards, John

 

[Stevos]

I wouldn't have thought that there was any reason why you couldn't get quotes (which implicitly require 'advice') now, at no cost, even if the work may be 12 months or so down the road.

Fair point, I may see what I can find out on that front. I think due to timescales it will be after the run (or runs) of duct have been installed

It's not just a matter of sizes - the diameters of SWA cables are freely available (most people who sell them will indicate the diameter). It's more a question of how easy it is to pull the cables through ducts of various sizes (adequate to accommodate the cable!) and lengths, and only those with appreciable experience of doing it will know the answer to that.

Sorry, yes that's what I was trying to get at.

I have the internal measurements of the twinwall duct I have (32mm internal), and a range of measurements for 3 core SWA

1.5mm2 -> 12.6mm diameter
2.5mm2 -> 14.1mm diameter
4mm2 -> 15.3mm diameter
6mm2 -> 16.6mm diameter
10mm2 -> 19.5mm diameter

(from Eland Cables)

Obviously the quality of the ducting and installation will have an impact (ie gently swept curves, hopefully not crushed, and the skill of the cable puller will have an impact, but I'm trying to get an idea of "on average" what sort of cable might be expected (not guaranteed) to go down a duct such as that.

I appreciate it may be outside the direct experience of many people, and a precise answer may not be possible, but any indications anyone could give based on experience could be very helpful, as it may help me decide whether to run two lengths of duct (for parallel cables, or something)

I suppose another option might be to buy some 6 or 10mm SWA and feed it through the duct before burial (which must be easier, but would presumably be potentially difficult to remove when buried), but that would take away a big benefit of the duct, and I was hoping to leave cable selection and supply to the eventual electrician

thanks

 

[JohnW2]

I wouldn't have thought that there was any reason why you couldn't get quotes (which implicitly require 'advice') now, at no cost, even if the work may be 12 months or so down the road.

Fair point, I may see what I can find out on that front. I think due to timescales it will be after the run (or runs) of duct have been installed

That's what I was suggesting you should avoid. For obvious reasons, you really need to know what cable the electrician is going to suggest and what size of duct they would be prepared to try to pull it through before you install the ducting!

I have the internal measurements of the twinwall duct I have (32mm internal), and a range of measurements for 3 core SWA ....... I'm trying to get an idea of "on average" what sort of cable might be expected (not guaranteed) to go down a duct such as that. ... I appreciate it may be outside the direct experience of many people, and a precise answer may not be possible, but any indications anyone could give based on experience could be very helpful ....

Yes, I understand that - but, as I said, you need someone with plenty of experience of pulling (or pushing) (or trying to pull/push!) SWA of various sizes through ducts of various sizes and lengths. That certainly isn't me, but maybe someone else here might be able to give you some idea. If I were in your position, I think I might just go for 'overkill' in terms of duct size, if I had to install it before really knowing what minimum size would be required!

Kind Regards, John

 

[DetlefSchmitz]

Certainly what I did was to put in 20m of 110mm duct for just 6mm SWA. It was worth it to me to be sure. I actually put in a second one in parallel for any data I might need.

As for pulling through, it went very easily. In my opinion pushing (anything but a fish tape) is just not an option.

In fact the builders who buried the duct for me, also lost the end of the pull string (big laugh!).

I bought a fish tape to pull a rope through and it was a 10 minute job.

I can't remember how much extra I paid for the larger ducting, but consider it money well spent.

 

[JohnW2]

Certainly what I did was to put in 20m of 110mm duct for just 6mm SWA. It was worth it to me to be sure. I actually put in a second one in parallel for any data I might need.

Indeed, as I said, I would personally go for overkill.

As for pulling through, it went very easily. In my opinion pushing (anything but a fish tape) is just not an option.

IME, with something as stiff as SWA, if one person is very gently pulling (basically just to discourage kinking etc.), nearly all the 'getting through' can be achieved by a person pushing at the other end.

Kind Regards, John

 

[ban-all-sheds]

In fact the builders who buried the duct for me, also lost the end of the pull string (big laugh!).

I bought a fish tape to pull a rope through and it was a 10 minute job.

Before you bury it replace the supplied drawstring with some more substantial lightweight rope.

 

[333rocky333]

Ive pulled 40 metres of 3core 2.5 through a 50mm duct with two natural 45 degree curves using the supplied string. Providing your in sync with the push/ pull its fine.
Though as Bas says pull in a bigger string first.
40mm with anything lke 6mm or bigger sounds iffy.

we have used drain rods in 100mm over 20 metres with other cables installed

50mm or larger with generous bends would allow use of drain rods if needbe and the drain rods at about 20mm thick can be used prior to burying to ensure that most average cables would go through with ease.

Though if you need to buy the rods you might just as well buy the SWA

 

[Stevos]

Okay thanks, that's what I was afraid of with the 40mm duct. I'm not sure less than 6mm will be sufficient for future needs.

I think the new plan may be to get some thicker SWA (6-10) and thread it through before the duct is buried, or just bin the duct idea altogether if it won't go in. I was hoping to avoid that partly to allow the electrician to choose / supply the cable, and partly to avoid having to handle the cable positioning which I suspect might be difficult.

I'm sure I can find some other use for the duct anyway.