circuits wired in flex?

[Ric2013]

Plumber here. I know this is an old thread, but still interesting.

From my perspective, heating controls are probably largely wired with flexible cable because we often need 4 cores, or 4 cores and earth.

For example, to reach distant motorised zone valves, or to carry L(p) L(ch) L(dhw) N(p) and E between a wiring centre and a programmer. I personally dislike running two parallel T+Es between 2 enclosures, not so much because it's a waste of materials and time, but because it seems somehow wrong and gives me an extra earth to terminate in busy enclosures.

3C+E is available as a solid cable, but I'm not sure that 4C+E is, or not that I've seen. So I'm forced into a dilemma: double up on solid cables, or use flexible cable. Any suggestions for improvement are welcome, and if a good spark in Colchester is on here that actually understands heating controls, then I may have some work for them some way down the line, if they want it.

 

[littlespark]

Old, @Ric2013 ?
It’s practically Jurassic!

I only recognise one name so far.


I think it was mentioned that although compliment, flex is more expensive, and therefor only used in short lengths to appliances or equipment.

In the instance of heating controls…. Most come with flex already attached and it’s a job of connecting all the ends together in the wiring centre…. (Or as we call them- “joint boxes”)

If there’s a longer length required, say to a room stat, then it would normally be 6243y 3core and earth.

 

[Ric2013]

Old, @Ric2013 ?
It’s practically Jurassic!

I only recognise one name so far.


I think it was mentioned that although compliment, flex is more expensive, and therefor only used in short lengths to appliances or equipment.

In the instance of heating controls…. Most come with flex already attached and it’s a job of connecting all the ends together in the wiring centre…. (Or as we call them- “joint boxes”)

If there’s a longer length required, say to a room stat, then it would normally be 6243y 3core and earth.

My personal, unqualified person's feeling, is that I agree that cost is probably the main (although not the only) driver behind the UK's continued use of solid core flat cable.

How would I connect to a 2 port valve with 6243 though? I need:

N(p)
L(call from stat)
L(p)
L(switched from "L(p)" by microswitch inside the 2-port valve)
Earth (not always)

which is 4-core and earth. We're back to 2 parallel lengths of 6242 cable (which is normally how I would do it - one cable is a switch wire and the other carries the live and neutral to power the 6W valve motor). In practice, you can get a bit of flexible cable and a Wago box and extend the tail, and I'm thinking this is a better solution in a way, the beauty of this being that future tradesmen will know that everything in that cable core goes to the same destination (not sure if this also reduces the EMF created compared with two parallel 6242s?).

Ideally, everything would be close to the joint box and all as you say above. In practice, houses evolve and it's easier to rewire than repipe. This means cylinder stats can often be remote from the programmer and the hypothetical joint box ends up being split between several enclosures. For example, if the cylinder stat and zone valve for the hot water are one end of a house, it makes sense to have a box near the two to switch the switched live to the valve motor rather than run an extra length of 6242 to act as a pair of switch wires all the way back from the joint box if that is at the other end of the house. But you still need 4 cores and earth between the 'main' and 'secondary' joint boxes.

My understanding was that if flexible cable is used it should be visible throughout its length, but not sure who made that rule and how precisely they defined 'visible', nor what happens when the only place the already-attached-flex HAS TO start under the floor because that is where the 2-port valve is or realistically has to go. Quite happy to run my concealed control cables in 6242 and 6243 (in fact, I usually do), but would be nice to know exactly why I'm doing it and when I have to do it, and can quite understand why many don't. (Better still I'd get a local sparky if I knew one that both understood heating controls and was interested in doing the work.)

Reason I bring this all up is #24. I find the plumbers vs electricians thing an example of what is wrong with the construction industry. I've heard your points of view and I thought you might appreciate a bit of insight from the other side. And interested... would you really run two number 2-core T+E rather than a 5 core flexible cable?

 

[nicebutdim]

Solid multicore cables are available and widely used, although not so much in domestic installations.

 

[Lucien Nunes]

It's an interesting discussion and your points are well reasoned. Much of the historical comment on the thread was rather polarised. It was from a time when there were two distinct and cliquey schools of thought on this forum about many topics which tended to override logical, fact-based discussion.

3C+E is available as a solid cable, but I'm not sure that 4C+E is, or not that I've seen

Not as flat T+E, but fire performance cable ranges usually include a 4C+E option as does NYY-J. And indeed many European styles of cable.

would you really run two number 2-core T+E rather than a 5 core flexible cable?

No, but I don't work in the domestic sector so I hardly ever use 6242. Conversely, 4C+E FP is a stock item for me. If I didn't have that, I would be happy with 3185Y. I also tend to work abroad at times so I even keep continental wiring cables on the shelf. And in an ideal world I would be happiest wiring it in 4L1 MICC.

(not sure if this also reduces the EMF created compared with two parallel 6242s?).

Not many people seem to have taken this into account until it was highlighted in the regs, although the phenomenon has always been there. TBH if the 2x 2C+E are adjacent, there's not much in it and I wouldn't worry about it. And in some cases each cable is a complete circuit (e.g. your motorised valve motor cable / switch cable example.)

 

[Ric2013]

It's an interesting discussion and your points are well reasoned. Much of the historical comment on the thread was rather polarised. It was from a time when there were two distinct and cliquey schools of thought on this forum about many topics which tended to override logical, fact-based discussion.

Thanks for your kind attitude - and the explanation! Actually, everyone who has replied to me has been very helpful and it is appreciated. I may not be an electrician (and I prefer to leave that side to others who have the right knowledge and tools... when I can), but it's really good to have a bit more understanding in the hope that any small bits I may end up taking on myself will be OTT (from lack of knowledge of what I could get away with) rather than bodged, even though they may not look as tidy as I'd like.

Not as flat T+E, but fire performance cable ranges usually include a 4C+E option as does NYY-J. And indeed many European styles of cable.

Just Googled NYJ-J. It looks to be a solid cored round cable. Presumably that can be installed in much the same way as 6242 and simply stripped and terminated inside an enclosure? Looks to be a good option, if so. Thank you.

Not many people seem to have taken this into account until it was highlighted in the regs, although the phenomenon has always been there. TBH if the 2x 2C+E are adjacent, there's not much in it and I wouldn't worry about it. And in some cases each cable is a complete circuit (e.g. your motorised valve motor cable / switch cable example.)

I've always wondered about that. I suspected that it might be the case if the cables were adjacent, but I'm happier hearing it from you. I knew an adjacent live and neutral through an appliance (motor, or lamp etc etc) essentially cancelled out, but, out of interest, is that the same for a switch cable i.e. where you have a live to a switch, and a switched live returning from the switch?

 

[Lucien Nunes]

Yes, any two equal currents (equal in both magnitude and phase) flowing in opposite directions will cancel. Or indeed any net zero sum of currents in any combination of conductors. I.e. if all the conductors serving any device or combination of devices run together, there will be no net longitudinal current (as per Kirchhoff's first law.) The EMF radiation (and in the case of a signal cable, susceptibility) will cancel better if the two cores occupy the same line through space. This can be achieved by making them coaxial, or by twisting them together so that they orbit around a common centre line. Both methods will be familiar in applications such as aerial and data cables, but the same technique can be used in very critical technical environments to minimise the fields radiated by power cables.

With normal power circuits, it starts to become of interest when there are large areas enclosed within current loops due to wide spacing between the two conductors forming a circuit, and/or the current contains higher harmonics that radiate easily. In a domestic setting, this normally occurs with 'traditional' 2-way switching, and with single-core sheathed wiring where the line loops via the switches but the neutral via the lights.

When I was about 14, I installed some lighting wiring using surplus 2-core MICC. With multiple switched circuits and fixtures but only two cores per cable, I did some creative reassignment of the conductors as they passed through fittings, to minimise the total number of cable runs. Some carried net zero longitudinal current but others had slightly different currents in the two conductors due to serving different numbers of points. Some of the lights were fluorescents with wirewound ballasts, which create a peaky waveform. I soon found that switching these on obliterated all AM radio reception within 20 feet of the wiring. The fluos radiate by themselves, but the loop aerials formed by my 'optimised' wiring runs made them worse.

 

[davesparks]

My understanding was that if flexible cable is used it should be visible throughout its length,

Wow, that's a very old regulation! It was indeed a requirement once upon a time, possibly not since the 13th edition, that installed flexible cables be short and visible throughout there length.
As I understand it this requirement was due to the less than ideal insulation available for cable manufacture at the time and it being somewhat more prone to failure.
This regulation is long gone, along with the one limiting the length of installed flexible cable.