Can you use two three cores for three circuits?

[SUNRAY]

My concern is eddy currents, if flow and return/ live and neutral do not follow exactly the same route. Low current garden lights will likely not produce much of a problem, none the less it is very bad practice to separate the two.

Basically - any current flowing through a conductor creates a magnetic field around it, which in the case of ac current is how a transformer operates. Any steel through which such a lone cable passes can have an eddy current induced into it, generating heat. Having both flow and return adjacent to each other, cancels this out completely. Basically, you never drill a hole in iron or steel and pass just the flow or return through it, always both through the same hole. You never run either flow or return by itself in a conduit, always both flow and return to avoid this issue.

This is all totally correct, however how many times recently have we seen questions on here relating to single and earth? I raised the interference issue [eddycurrents] not many years back and received criticism from many posters and not a single defence. As an AFILS installer and user I'm very aware of the issue and all of a sudden I see agreement with my thoughts.

Anyway back to the question in hand;
How are these cable run?
Are they very close together or even in a conduit?

Also, what do you mean by 3 circuits, some applications are easily catered for with what you have?
More details please and pictures always help.

 

[SUNRAY]

My concern is eddy currents, if flow and return/ live and neutral do not follow exactly the same route. Low current garden lights will likely not produce much of a problem, none the less it is very bad practice to separate the two.

Basically - any current flowing through a conductor creates a magnetic field around it, which in the case of ac current is how a transformer operates. Any steel through which such a lone cable passes can have an eddy current induced into it, generating heat. Having both flow and return adjacent to each other, cancels this out completely. Basically, you never drill a hole in iron or steel and pass just the flow or return through it, always both through the same hole. You never run either flow or return by itself in a conduit, always both flow and return to avoid this issue.

This is all totally correct, however how many times recently have we seen questions on here relating to single and earth? I raised the interference issue [eddycurrents] not many years back and received criticism from many posters and not a single defence. As an AFILS installer and user I'm very aware of the issue and all of a sudden I see agreement with my thoughts.

Anyway back to the question in hand;
How are these cable run?
Are they very close together or even in a conduit?

Also, what do you mean by 3 circuits, some applications are easily catered for with what you have?
More details please and pictures always help.

 

[333rocky333]

That changes things, you only have 1 circuit and 3 switchlines, providing the Neutral and E is in the same sheath as 1 or 2 switchlines, thats fine
Essentially up to 4 switchlines and 2 N and 2 E

 

[SUNRAY]

That changes things, you only have 1 circuit and 3 switchlines, providing the Neutral and E is in the same sheath as 1 or 2 switchlines, thats fine
Essentially up to 4 switchlines and 2 N and 2 E

That's where I was aiming my previous question but sadly I got distracted by TV and took far too long to make my post.

 

[JohnW2]

I did not get that parralel .... bit can you elaborate please what they mean please

It's a very rare situation they're talking about when, because one conductor does not have sufficient CSA for the current involved, one uses two (or more) conductors in parallel- so, for example, one could have the brown and blue of one 2-core cable connected (at both ends) to the brown and blue of a 'parallel' cable.

Kind Regards, John

 

[JohnW2]

My concern is eddy currents, if flow and return/ live and neutral do not follow exactly the same route.

In low-current situations, eddy currents are not really the issue - the main theoretical problem is that if the L and corresponding N currents are not flowing through conductors in very close proximity (i.e. in the same cable), then there electromagnetic fields do not 'cancel' which can, for example, result in 50Hz 'hum' in audio equipment etc.

.... none the less it is very bad practice to separate the two.

'Very bad practice' or not, it was once common in two-way lighting circuits (fed with L and one end and N at the other).

Kind Regards, John

 

[pedr0]

Diagram attached. The stuff in pencil is what is currently there. The green, purple and orange felt tip describes what I'd like to add: ie three sets of lights, each set on its own switch inside (where the feed is) .

Are they very close together or even in a conduit?

The two 3 core cables follow the same path, and were laid at the same time.
But I can't tell how close they are together as they run behind the interior wall before emerging in the garden.

Edit :They are not in a conduit while running through the wall because I can see where they emerge in the garden before going into an armoured bendable pipe.

Edit 2: see a couple of posts below for the image

 

[333rocky333]

It's a very rare situation they're talking about when, because one conductor does not have sufficient CSA for the current involved, one uses two (or more) conductors in parallel- so, for example, one could have the brown and blue of one 2-core cable connected (at both ends) to the brown and blue of a 'parallel' cable.

Kind Regards, John

Ok thanks seen it done with 4 big fat singles, not with 2 core though

 

[333rocky333]

Diagram attached.

 

[pedr0]

Fail.

Diagram attached now I hope

 

[JohnW2]

Ok thanks seen it done with 4 big fat singles, not with 2 core though

As I said, I'm sure it's very rare. I've not sure that I've ever seen it done with any type or size of cable in an electrical installation (I have seen it in car electrics, and other ELV situations). It would presumably be very rare that there was a particularly good 'excuse' (apart from laziness and cost), since it would virtually always be possible to find a larger cable that would be adequate on its own.

Kind Regards, John

 

[333rocky333]

Fail.

Diagram attached now I hope
View attachment 226682

Do as Adrian says you will be fine, regarding the load its very unlikely you will overload the 1mm Neutral even with 2 switchlines loaded with garden lighting

 

[pedr0]

Great. On one of the switch lines can I have two 'spurs', one for 240v fittings and one for 12v with a transformer? (all turned on and off at the same time by a single switch of course )

Edit:excuse any incorrect terminology, eg wrong use of the word spur

 

[SUNRAY]

As I said, I'm sure it's very rare. I've not sure that I've ever seen it done with any type or size of cable in an electrical installation (I have seen it in car electrics, and other ELV situations). It would presumably be very rare that there was a particularly good 'excuse' (apart from laziness and cost), since it would virtually always be possible to find a larger cable that would be adequate on its own.

Kind Regards, John

Try saying that to the person tasked with providing the 1200A 3 ph feed for a chiller on the roof from the switch room at the other end of the building 10 floors below.

 

[pedr0]

The fact that you guys have just found me a fourth line gives me an idea.Perhaps I can use that fourth one to put a light in my shed. In that case though, The switch for the shed light would be in the shed (ie downstream of the external junction box) rather than with the other switches indoors. Would that still be OK?