# Armoured cable - radius of bends?



## robgul (20 May 2022)

I'm going to run a 2.5 T&E Armoured cable from the house about 15 metres to an outbuilding, fixed to a wall. That's straightforward - my question is how tight can I make the bends in the cable where it turns corners? 

The turns, if I can do them are 90 degrees - it's how tight I can make the radius that's the issue - connections will, of course, be "to regs" - I don't want to have to use any connection boxes to turn the corners.


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## Lorenzl (20 May 2022)

6 - 8 times the cable diameter depending on the exact style of cable. You could find the exact information if you know the manufacturer as they should publish it.

Vertical corners will look OK but horizontal ones won't unless you cut a slot in the corner of the wall


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## Lorenzl (20 May 2022)

You might get a tighter bend radii with xple cable.


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## robgul (20 May 2022)

Lorenzl said:


> You might get a tighter bend radii with xple cable.



I think that's XLPE ? - but doesn't appear to be armoured? - as it's going low down on the wall along the back of flower beds I'd be concerned about my wife hitting it with loppers/secateurs/strimmer etc.


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## pe2dave (20 May 2022)

Just a thought. Could you bury it to create a greater loop whilst going round the exterior corner?


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## Spectric (20 May 2022)

First question is what is the cable, I assume it is armoured and not twin & earth so how many cores as this will impact the max radius ? When running armoured cables round corners they should not be forced and just allow them to decide. I assume that the outbuilding does not have any extranous conductive parts such as a metal frame or cladding otherwise some changes will be needed and how was the 2.5mm decided upon?


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## robgul (20 May 2022)

pe2dave said:


> Just a thought. Could you bury it to create a greater loop whilst going round the exterior corner?



I've re-thought the way it's going to be and it will now climb the wall and then turn across a "bridge" to get to the house (i.e. there'll be an arch over the passage between the wall and the house.) - and the corner that it was going to go round has concrete on the ground!


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## robgul (20 May 2022)

Spectric said:


> First question is what is the cable, I assume it is armoured and not twin & earth so how many cores as this will impact the max radius ? When running armoured cables round corners they should not be forced and just allow them to decide. I assume that the outbuilding does not have any extranous conductive parts such as a metal frame or cladding otherwise some changes will be needed and how was the 2.5mm decided upon?



It's 6943X - and as the OP says 2.5 T&E Armoured - as recommended by a qualified electrician who has also advised on the connections/outlet. The supply is to run some low-ish powered garden machinery and possibly some lights on the odd occasion - and the building is wooden.


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## pe2dave (20 May 2022)

robgul said:


> I've re-thought the way it's going to be and it will now climb the wall and then turn across a "bridge" to get to the house (i.e. there'll be an arch over the passage between the wall and the house.) - and the corner that it was going to go round has concrete on the ground!


So where are your 'right angles' now? ground going up the wall, external wall corner? Not clear?


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## morqthana (20 May 2022)

robgul said:


> I'm going to run a 2.5 T&E Armoured cable from the house about 15 metres to an outbuilding, fixed to a wall. That's straightforward - my question is how tight can I make the bends in the cable where it turns corners?


Nowhere near tight enough.

If you can accomodate a change in height, what you can do is to sweep the cable up (or down) as it approaches the corner, so it's vertical when it gets there, ease it around the corner as it goes up (or down) then turn it horizontal.



robgul said:


> The turns, if I can do them are 90 degrees - it's how tight I can make the radius that's the issue - connections will, of course, be "to regs" - I don't want to have to use any connection boxes to turn the corners.


No regs against junction boxes.

What will the cable supply?
Where does it originate?
Where is the RCD protection?
Is it a new circuit?
What will the glands be installed in?
Did you buy extra cable to practice terminating it?


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## robgul (20 May 2022)

morqthana said:


> Nowhere near tight enough.
> 
> If you can accomodate a change in height, what you can do is to sweep the cable up (or down) as it approaches the corner, so it's vertical when it gets there, ease it around the corner as it goes up (or down) then turn it horizontal.
> 
> ...



New plan has gentle curves which will work with the cable - and YES/OK/COMPLIES (all advised by a qualified electrician) - to all your comments, or already answered 

I've done all this before but a while ago.


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## pe2dave (20 May 2022)

Daft one @robgul - but seems to apply. Electricity doesn't like going round corners!
Seems you've got it though. 
Stressed cable, outside, you can guess the consequences over a long period.


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## Spectric (20 May 2022)

6943X is 2.5mm three cored armoured, it is not twin and earth. 6943X2.5MM BASEC Approved 6943X Black 3 Core Steel Wire Armoured Cable 2.5mm (priced per metre) - Shop4 Electrical

Anyone in the game would know that, so is this qualified electrician called Joe by any chance. 

If you measure the OD it will be around 15mm, the minimum bend radius will be 90mm, it will probably not notice and is not really worth the worry but if you want to hide the corners then garden ordaments or flower baskets. Start running 185mm 4 core and then bend radius can be a real headache!


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## robgul (20 May 2022)

Spectric said:


> 6943X is 2.5mm three cored armoured, it is not twin and earth. 6943X2.5MM BASEC Approved 6943X Black 3 Core Steel Wire Armoured Cable 2.5mm (priced per metre) - Shop4 Electrical
> 
> Anyone in the game would know that, so is this qualified electrician called Joe by any chance.
> 
> If you measure the OD it will be around 15mm, the minimum bend radius will be 90mm, it will probably not notice and is not really worth the worry but if you want to hide the corners then garden ordaments or flower baskets. Start running 185mm 4 core and then bend radius can be a real headache!



OK - my terminology for the 3 core that is to be used as T&E - he just gave me the number of the cable.

I'm done with this thread - cable ordered, I should get the job finished during the coming week . . . water is involved too!!


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## Spectric (20 May 2022)

How did you get on with the corners?


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## robgul (20 May 2022)

Spectric said:


> How did you get on with the corners?


Err - you're getting ahead of yourself - cable hasn't arrived yet . . . . .


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## mikej460 (20 May 2022)

I solved this by sweeping into the workshop then swept gently back to the inside wall. The resulting small bulge is hidden behind a cupboard.


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## HOJ (20 May 2022)

robgul said:


> I'm done with this thread - cable ordered, I should get the job finished during the coming week . . . water is involved too!!



Not the corners or bending radii I'd be worried about....


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## morqthana (21 May 2022)

Spectric said:


> 6943X is 2.5mm three cored armoured, it is not twin and earth. 6943X2.5MM BASEC Approved 6943X Black 3 Core Steel Wire Armoured Cable 2.5mm (priced per metre) - Shop4 Electrical
> 
> Anyone in the game would know that, so is this qualified electrician called Joe by any chance.


Oh come on - he said it was armoured, and he said it was 6943X. So he said it was "T&E" armoured instead of "3-core" armoured.

Wow.

I could point out that here:








How to correctly wire 2-way switch for ring main


Currently I have a spur from the ring main, but I'm planning on adding more sockets. I can't add a 13 amp fuse because I expect to be using more than 13 amps, therefore, I am going to convert the spur into a ring main extension, as in the following diagram: I'd like to put in a 2 way switch so...




www.ukworkshop.co.uk




you use the terms "ring main" (no, it's "ring final") and "live" (no, it's "line"), but I won't, nor will I ask if your name is Joe.


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## Stevekane (21 May 2022)

This is all great fun and I cannot resist jumping in. First a sensible bit,,,are you talking about 3 core plus earth or as you said “twin and earth”? The reason I ask is that if you go for the “4 core stuff” you can for instance use that 4th wire to switch on say an outside light on the shed from inside the house which can be very handy,,now a question, why cant you just put your foot on a bit of armoured cable and bend it as tight as you can, I wouldnt have thought that the plastic insulation would be damaged and in any case your constrained in how tight you would get it by the twisted armour and outer caseing?
Steve.


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## Spectric (21 May 2022)

Stevekane said:


> now a question, why cant you just put your foot on a bit of armoured cable and bend it as tight as you can,


Because it does not like it, the outside will be in tension whilst the inside will be under compression and there is a limit to how far the armour can accomodate these forces. It is not a major problem with SWA's upto 25 to 35mm CSA but once the cable uses shaped conductors then it becomes an issue for everyone.


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## Stevekane (21 May 2022)

Many thanks Roy, 25mm to 35mm csa (individual?) cables,,I obviously mjssed the bit about the OP recreating Dr Frankensteins lab in his shed! 
But seriously, I looked up shaped conductors, never seen them before and a clever idea, and I can see that they wouldn't take kindly to being tightly bent. We learn something every day,,
Steve.


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## Spectric (21 May 2022)

16mm or 25mm are the typical supply cables to a domestic property, 60 / 100 amp DNO fuse. Once you get very large csa cables, having them round makes for a very large diameter cable, shaping them like the segments of a pie makes for a more compact cable. Also the armour can be aluminium because it is non magnetic and also the cores can be aluminium, this is the heavy end of electrical engineering and best left to the younger guys.


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## nickds1 (21 May 2022)

Spectric said:


> 6943X is 2.5mm three cored armoured, it is not twin and earth. 6943X2.5MM BASEC Approved 6943X Black 3 Core Steel Wire Armoured Cable 2.5mm (priced per metre) - Shop4 Electrical
> 
> Anyone in the game would know that, so is this qualified electrician called Joe by any chance.
> 
> If you measure the OD it will be around 15mm, the minimum bend radius will be 90mm, it will probably not notice and is not really worth the worry but if you want to hide the corners then garden ordaments or flower baskets. Start running 185mm 4 core and then bend radius can be a real headache!


I redid a small data centre in Dubai where we had a 400KVA 3-phase Volvo generator on the roof and 7 floors below, the ATS, UPSs and machine room...

The armoured cables between the ATS and genset were humungous, not least because of having to travel 7 floors with minimum loss. The cable was one piece, made to order and pulling it up through the building risers required a 20tonne capacity crane.

I totally hate big cables. To get even a start at bending it we had to use high temperature heating jackets to get the cable and cores to move at all...

When you get into the world of high voltage transmission lines, the world of cable design gets very complicated - there's a lot of elements of the cable design related to minimising losses, particularly resistive, electromagnetic and from corona discharge.


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## morqthana (21 May 2022)

The problem with normal cables is that if you bend them too tight you'll damage the insultion - maybe not immediately, but when the conductors get warm they can push their way to the outside, and end up insufficiently protected.

But it is probably impossible to bend armoured too tight by hand.


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## morqthana (22 May 2022)

Stevekane said:


> This is all great fun and I cannot resist jumping in. First a sensible bit,,,are you talking about 3 core plus earth or as you said “twin and earth”?


He's talking about 3-core SWA, using the cores as L/N/E. He just referred to that as armoured T&E, which I don't think is as heinous or indicative of incompetence as some would like to make out.




Stevekane said:


> The reason I ask is that if you go for the “4 core stuff” you can for instance use that 4th wire to switch on say an outside light on the shed from inside the house which can be very handy,,


Good idea, but the cable choice ship has sailed. He could use just the armour as the earth (or cpc if you prefer) - and free up a core that way, if he wanted.


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## morqthana (22 May 2022)

nickds1 said:


> I redid a small data centre in Dubai where we had a 400KVA 3-phase Volvo generator on the roof


Why the <whatever> did they drag it all the way up there?


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## Spectric (22 May 2022)

That is like referring to a horse as a unicorn, one exist whilst the other is imaginary except everyone knows that.


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## Spectric (22 May 2022)

morqthana said:


> Why the <whatever> did they drag it all the way up there


Up there or on the ground, either way you would still need the risers but roof space may be available whilst ground space had other uses. I bet they had some issues with storing the fuel for it when it came to fire safety!


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## OldGreyDog (22 May 2022)

Hands up… I confess that I have a 2.5mm armoured leading to my shed thats bent a little tight around a bit of brickwork although its been in place almost ten years and has given no trouble. I bent it by hand and at the time was unaware of a specific minimum radius. this bit is in the shade, below a decked area (but secured to a brick wall not touching any timber). This spur has its own 16a circuit breaker in a DP switched box, so I think i’ll leave it be for now. I’ll know better next time!


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## Stevekane (22 May 2022)

morqthana said:


> He's talking about 3-core SWA, using the cores as L/N/E. He just referred to that as armoured T&E, which I don't think is as heinous or indicative of incompetence as some would like to make out.
> 
> 
> 
> Good idea, but the cable choice ship has sailed. He could use just the armour as the earth (or cpc if you prefer) - and free up a core that way, if he wanted.


Quite, and I certainly wouldn't argue with that, but just as a matter of intrest, I had a vague notion that now using the armour as an earth conductor even though its earthed was verboten,,handy to know if its still okay to do?
Steve.


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## morqthana (22 May 2022)

It's absolutely fine, apart from some large cables (far larger than you'd ever ecounter domestically) where the armour isn't big enough. Basically steel is a much poorer conductor than copper, so the cross-sectional area of the armour needs to be greater than the csa of a copper earth conductor, and over a certain cable size it isn't OK.


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## nickds1 (22 May 2022)

Spectric said:


> Up there or on the ground, either way you would still need the risers but roof space may be available whilst ground space had other uses. I bet they had some issues with storing the fuel for it when it came to fire safety!


Indeed there was nowhere inside the building or outside.

The fuel (diesel) is stored as part of the genset container which was craned onto the roof (which was built to take it).

The main problems are that we then had to build a sunshade for it as in summer we hit 45C, plus the fuel has to be changed every 12 months (because it rots) and there is no lift access to the roof, which means that a team of poor sods has to empty the tank (24 hour running qty) into Jerry cans then carry it down the access ladder to the stairs to the top floor, then take it down in the lift and to a waiting truck.

Then the reverse - carrying 1000 litres or so back up the building...

Did I mention that it gets quite warm there?


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