Another 12v Volt Drop Query

[ban-all-sheds]

If it were me I'd consider using cable tray fixed to the concrete posts and making a wooden cover for it out of something which matched the fence, mounted, 20-30cm below the height of the lowest panels, and put an LED rope light on the underside, so that it looked like a lighting feature, not a cable trunk.

 

[SimonH2]

Pity you didn't think about this earlier ...
Could have had a small duct buried in the bottom of the planters, or even along the whole route ...
BASs suggestion doesn't sound bad, something like this might just do - run your power cable along the back of it, and a rope light along the front (neatly cable tie to front and back rails). Being an open basket means you can put the rope light inside it (no worries about it sagging between fixings). Put it on both fences and it'll look more like it's a lighting feature than a cable run.

However ...
You need to be very careful how you fix things to the fence posts. While it's tempting to drill them, there's actually not a lot of concrete and you risk splitting the concrete, hitting the steel bars that are inside, or just letting moisture in that makes the bars rust and split the post. Replacing the fence posts would be a real p.i.t.a. - especially as you've now got structures over their (presumably) concrete footings. Been there, done that - the replacing bit, not the splitting bit* You'd need to make some sort of clamp to fix things with - never seen anything off the shelf for that.

Following BAS's lead - could you string a supporting wire along the garden (right down the middle) and hang a string of lights (and your power cable) along it ?

Bet you've planted lots of stuff already ...
How about, digging the soil out of the planters, drilling holes in the ends are required, and bury an armoured cable in the bottom ? Might be easier on the left and go around the bottom end of the garden.


* We still had (what was left of) the original fencing (concrete posts, wire, and wood pickets) from when the houses were built in (we think) the 1940s. Lasted surprisingly well, most of the wood was still there, most of the wire was still there, and most of the posts were still intact. Most of the posts just pulled out together with a large lump of concrete on the bottom, but one I had to break up the concrete in situ as it had been built over on one side - took me quite a lot of effort getting that one out.

As an aside, I'd be concerned about the fence panels going down to ground level with no gravel boards. It means the wood panels will be constantly damp at the bottom and will rot faster because of it. Hard to tell, but it looks like both neighbours have areas where the ground level is above the bottom of the panels - meaning that the wood is actually underground.

 

[ban-all-sheds]

You'd need to make some sort of clamp to fix things with - never seen anything off the shelf for that.

https://www.bing.com/images/search?q=postfix+slotted+bracket

 

[SimonH2]

Amazing, the number of places that sell slotted posts but have never heard of these
That could well make a project I have in mind "quite a bit easier"

 

[Adam Withers]

That's the usual objection to fixing to fences - that and the fact that even if they don't blow down they move about, and that can stress joints and connections.

But you have concrete fence posts - as long as they are properly fixed at the base, they would be absolutely fine for fixing cables to. The only problem would be that if you didn't use steel conduit then the cable would sag, as the supports would be too far apart.

Yeah - this is one of the options the electrician mentioned, but he advised that steel conduit is a pain to run SWA cable in - I assume due to the internal diameter of the conduit is similar to the SWA cable - is this correct - also it would look a bit rubbish on the fence. He also said that drilling into those concrete posts is also a pain.

It may prove difficult anyway - what do you mean by "certify" and "get an electrician"?

I may not be using the right terminology, but surely the electrician I employ to do the work (or terminate the connections to the mains) will need to sign it off/certify it as their work?

Shame that you didn't think about this before you had the turf laid.....

As I mentioned in my original post, this is a long story, but the short version is that the company I got in to do the work advised they would run the cable up to the shed as I wanted, but they left it to the end of the job and they didn't run it correctly. It was not part of the schedule of works, so I couldn't come back to them on it. I assumed (obviously wrongly) they would know the reg in running the cabling as again I assumed (again wrongly) they would be doing it all the time (either that or their other installations are also against the regs). As they say, assumption is the mother of all f***ups

 

[Adam Withers]

If it were me I'd consider using cable tray fixed to the concrete posts and making a wooden cover for it out of something which matched the fence, mounted, 20-30cm below the height of the lowest panels, and put an LED rope light on the underside, so that it looked like a lighting feature, not a cable trunk.

That is a good idea - I will look into that and also those postfix brackets you also linked - may be a way to go!

 

[Adam Withers]

Pity you didn't think about this earlier ...
Could have had a small duct buried in the bottom of the planters, or even along the whole route ...
BASs suggestion doesn't sound bad, something like this might just do - run your power cable along the back of it, and a rope light along the front (neatly cable tie to front and back rails). Being an open basket means you can put the rope light inside it (no worries about it sagging between fixings). Put it on both fences and it'll look more like it's a lighting feature than a cable run.

Yep - See my previous post as it is explained there
I think this would be a more stable solution to the tray: https://www.tlc-direct.co.uk/Main_Index/Cable_Tray/
But yeah the run on the fence would look good. I don't think I could do it both sides as the left is not my fence and the neighbour will probably not want me doing this. :-/

However ...
You need to be very careful how you fix things to the fence posts. While it's tempting to drill them, there's actually not a lot of concrete and you risk splitting the concrete, hitting the steel bars that are inside, or just letting moisture in that makes the bars rust and split the post. Replacing the fence posts would be a real p.i.t.a. - especially as you've now got structures over their (presumably) concrete footings. Been there, done that - the replacing bit, not the splitting bit* You'd need to make some sort of clamp to fix things with - never seen anything off the shelf for that.

Yeah - I agree on the concrete drilling, but BAS as linked a possible solution to hanging things off the posts - will need to look into this.

Following BAS's lead - could you string a supporting wire along the garden (right down the middle) and hang a string of lights (and your power cable) along it ?

We had thought about running a Catenary above the fence line, but I think would look rubbish - the wall at the back is not ours so you would need to put a post up to connect it to. I don't really like the idea of running the light, but each to their own

Bet you've planted lots of stuff already ...
How about, digging the soil out of the planters, drilling holes in the ends are required, and bury an armoured cable in the bottom ? Might be easier on the left and go around the bottom end of the garden.

Only a few plants, as we have resigned ourselves to not running the cable in the beds. We had thought about it, but there is a load of soil there and we would probably destroy the lawn in the process. Closer to the house we may still end up see the cable in places where it enters the beds and there is trying to bend a SWA around may cause issues. Basically a major faff I don't really want to go down.

* We still had (what was left of) the original fencing (concrete posts, wire, and wood pickets) from when the houses were built in (we think) the 1940s. Lasted surprisingly well, most of the wood was still there, most of the wire was still there, and most of the posts were still intact. Most of the posts just pulled out together with a large lump of concrete on the bottom, but one I had to break up the concrete in situ as it had been built over on one side - took me quite a lot of effort getting that one out.

As an aside, I'd be concerned about the fence panels going down to ground level with no gravel boards. It means the wood panels will be constantly damp at the bottom and will rot faster because of it. Hard to tell, but it looks like both neighbours have areas where the ground level is above the bottom of the panels - meaning that the wood is actually underground.

We do have gravel boards on our fence (the right side) and is it not in contact with the soil. The left is neighbours.

 

[SimonH2]

Yep - See my previous post as it is explained there
I think this would be a more stable solution to the tray: https://www.tlc-direct.co.uk/Main_Index/Cable_Tray/

No, that would be rubbish for what you want.
Light duty cable tray is very flexible and needs lots of supports - OK in the right place, but for what you want it would be rather poor. No way you could have 6ft spans without oodles of sag.
Heavy duty cable tray is, well, heavy - as well as being more expensive. Wire basket is a good compromise (very strong for it's weight) and would span 6ft provided you (and everyone else) avoid the temptation to hang things off it
it would probably be worth you finding a good local electrical wholesaler and ask them to show you the three types. It was a lot of years ago now when an electrician friend of mine told me about wire basket - so uncommon that the wholesaler didn't stock it and had to order it in. All I'll say is that I don't think I've used tray any time since !

 

[JohnW2]

No, that would be rubbish for what you want. ... Light duty cable tray is very flexible and needs lots of supports - OK in the right place, but for what you want it would be rather poor. No way you could have 6ft spans without oodles of sag. Heavy duty cable tray is, well, heavy - as well as being more expensive. Wire basket is a good compromise

I must say that if I were contemplating running SWA along a fence in/or something in the manner described (fairly high up and very visible) (which I probably wouldn't), I think that the 'something' I would be thinking of would probably be some sort of conduit/pipe - which wouldn't need to be all that big for one to be able to pull modest-sized SWA through (for straight runs).

In reality, I would probably be thinking more in terms of putting any such 'conduit/pipe' on, or near, the ground.

Kind Regards, John

 

[SimonH2]

High up, it wouldn't need to be SWA. Might need a bit more care in selection of route either end though.

 

[JohnW2]

High up, it wouldn't need to be SWA. Might need a bit more care in selection of route either end though.

Exactly. In practice I suspect that I would probably end up using SWA, because of where it was having to go at either end of the 'straight and high up' bit. However, as I said, I probably would not go for the 'high up' approach, anyway.

Kind Regards, John

 

[Adam Withers]

Thanks guys.

I am going to have a good look at the weekend on trying to run a cable behind the beds, but I suspect it is not going to be possible as the bed walls are right up against the concrete posts. I may be able to lift the fence panels a bit to get access from behind and knock out of the mortar on the beds a bit to route the cable, but this could loosen the bricks, but will see.

 

[ban-all-sheds]

No, that would be rubbish for what you want.
Light duty cable tray is very flexible and needs lots of supports - OK in the right place, but for what you want it would be rather poor. No way you could have 6ft spans without oodles of sag.

Surely it would be this way up:

not this way

?

 

[SimonH2]

It could be, and often is used like that - but it would flap around like bunting. Could fix it to the panels as well as the posts, but then you're back to fixing to the wooden panels.

 

[SUNRAY]

In any given length of cable, voltage drop is proportional to current.

So the total drop of any cable depends on its length, and how much current is flowing - the longer the cable, the greater the drop. The higher the current, the greater the drop.

It follows that one characteristic of a cable is its voltage drop for a particular current over a particular length and at the sorts of currents and lengths found in low and extra-low voltage final circuits, millivolts (of drop) per amp per metre are the most sensible unit.

View attachment 157658

So that table shows that, to use your scenario, 2.5mm² cable will have a drop of 18mV for every amp of current for every metre of length.

If you've got a 10A load, over your 20m the voltage drop will be

(18 x 10 x 20)mV = 3.6V

I've never done the comparisin before as I generally find it easier to use the resistance and calculate from there. I have always found this to be pretty accurate.
OSG Table 9A (16th ed) which again I've found to be reliable, shows 2.5mm² as 14.82mΩ/m. 14.82x10x20 = 2964mV drop
But 4D2B (16th ed) clearly shows 18mV/A/m which comes out as 3.6V as shown by BAS or a discrepancy of 21%