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Using 7 Core Armoured as Twin and Earth ?

Discuss Using 7 Core Armoured as Twin and Earth ? in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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keithy1959

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My daughter has some 7 core armoured cable running to her garage which looks to be 1m2 or possible 1.5m2. It carries a 2-way external light switch connection to switch on 2 external lights ( house and garage) from either the house or the garage, and there is also a single 13amp socket connected. I have told them to use the socket for a lead lamp in the garage only - ie no heaters, etc. There is no RCD from what I can see.

An electrician has suggested that if the switching was removed, the cables could be paired up to run a 13a supply and add an external PIR light, saving the need to replace the 7 Core with 3 Core Armoured ( it's >20m length).

This doesn't sound right to me but would make perfect sense if its within regs - any comments most welcome.
 
Your description is a little hard to fathom out, any possibility of drafting a sketch of the wiring, and / or a photograph of the connections, and possibly get hold of a different Electrician, preferably one who knows what he is talking about.
 
Assuming you no longer require the two way switching yes you can parallel the conductors. Depending on the existing protective device the existing set up may be okay not taking any volt drop issues into consideration.
 
There is not 1.0mm size in the regs, and I have looked at some manufacturers and the smallest they do is 1.5mm. So most prob your cable is 1.5mm
Nothing wrong with pairing up the cables in the 7 core cable, as I presume the electrician will test it before doing anything.
 
Spoon said:
There is not 1.0mm size in the regs, and I have looked at some manufacturers and the smallest they do is 1.5mm. So most prob your cable is 1.5mm
Nothing wrong with pairing up the cables in the 7 core cable, as I presume the electrician will test it before doing anything.
Click to expand...
Spoon like your post,and agree with you, but I don't like doubling up cores, it's not something I have personally ever done, and not something I would necessarily do, like you say nothing to stop you doing so, just me being an old fert I guess.
 
Pete999 said:
Spoon like your post,and agree with you, but I don't like doubling up cores, it's not something I have personally ever done, and not something I would necessarily do, like you say nothing to stop you doing so, just me being an old fert I guess.
Click to expand...

We did have a contract that had 2 x 400mm XLPE/PVC/SWA/PVC cables going from the phase shift transformers to the dist cabinets..
 
Spoon said:
We did have a contract that had 2 x 400mm XLPE/PVC/SWA/PVC cables going from the phase shift transformers to the dist cabinets..
Click to expand...
That's a distribution service Spoon, bit of a step down from doubling up on final circuits, but I get your drift.
 
Pete999 said:
That's a distribution service Spoon, bit of a step down from doubling up on final circuits, but I get your drift.
Click to expand...

Yeah, biggest I've designed. 3 x 3 phase transformers & 4 dist cabinets.

haha.... The principle is the same mate. It saves the OP getting a new cable installed, if the existing 7 core is fine.
 
We double up conductors on some jobs to get around voltage drop, often this is using hybrid cables containing copper and fibre.

In domestic I would make a note at source as to why the cables are doubled up, no doubt someone in the future might know no better and decide to remove a couple of the cores.
 
westward10 said:
Makes no difference providing they are equal cross sectional area.
Click to expand...
I know you don't need to point out the obvious Westy, as I said earlier, but I do take issue with doubling up conductors on final circuit conductors, as they are planned and more care is taken during installation, hence a safer install.
My issue is doubling up as a remedial action, I realise it's OK to do so, but just because it is safe to do so , doesn't mean I have to like it.
 
Pete999 said:
I know you don't need to point out the obvious Westy, as I said earlier, but I do take issue with doubling up conductors on final circuit conductors, as they are planned and more care is taken during installation, hence a safer install.
My issue is doubling up as a remedial action, I realise it's OK to do so, but just because it is safe to do so , doesn't mean I have to like it.
Click to expand...
It is an existing cable so make use of what you have. The OP has asked is it okay, yes it is. Saying you don't like it is clouding the issue.
 
Pete999 said:
I know you don't need to point out the obvious Westy, as I said earlier, but I do take issue with doubling up conductors on final circuit conductors, as they are planned and more care is taken during installation, hence a safer install.
My issue is doubling up as a remedial action, I realise it's OK to do so, but just because it is safe to do so , doesn't mean I have to like it.
Click to expand...
I think my post may be a bit misleading, Distribution doubling up is usually a planned install, which is monitored and planned, where as final circuit doubling is often done as an after thought, or as remedial action. This is what I was trying to put over.
 
westward10 said:
It is an existing cable so make use of what you have. The OP has asked is it okay, yes it is. Saying you don't like it is clouding the issue.
Click to expand...

I dont think any of @Pete999 posts have clouded the issue. Just that he dislikes the idea, unless its been designed that way.
 
Pete - will do - I was struggling to explain it in words !!

I'm back up there tomorrow, so I'll try and sketch it as much as I can, but I suspect the 7 core is connected to the house wiring, somehere under a tiled (suspended ) floor.
 
Paignton pete said:
Obviously in this case they are equal cross sectional areas, but why must they be.

I can understand it would make design easier, but not sure of the specific reasoning.

Cheers
Click to expand...
If they are the same csa the resistance is equal so the load is balanced across the two. Differing csa will result in an imbalance across the two.
 
westward10 said:
If they are the same csa the resistance is equal so the load is balanced across the two. Differing csa will result in an imbalance across the two.
Click to expand...

Trying to get my head round this and not disagreeing, just like to know the ins and outs of stuff.

Does the resistance need to be equal as it's the overal resistance and csa that the current would be traveling.

Wouldnt the current be greater down the larger conductor than the smaller?
Due to current traveling down the path of least resistance would it would balance itself out proportionately between conductors.
 
MDJ said:
Can I ask why?
Click to expand...

Out of ignorance, perhaps. I know the math (area) is OK, but it seems a bit like making a ring circuit from the wrong cable - I appreciate the correct breaker would fix that, but I was interested from a good practice point of view.

From an installation point of view, the house is on a 1 in 3 slope, with the garage floor roughly level with the bedroom ceilings, so replacing the cable is going to be a pain. I guess I'm just checking this wasnt a "just enough" solution to save the grief.
 
keithy1959 said:
Pete - will do - I was struggling to explain it in words !!

I'm back up there tomorrow, so I'll try and sketch it as much as I can, but I suspect the 7 core is connected to the house wiring, somewhere under a tiled (suspended ) floor.
Click to expand...

Not wishing to state the obvious but doubling up may only be possible if you can locate the connections ........ at both ends
 

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