2 circuits in one cable.

[oscar21]

Strange on this, we are wiring an extension at the moment and I would like to 3 way the (currently 2 way) landing switch to the new bedroom so there is a switch near by for the stairs. The property was supposedly re-wired when the couple bought the place about eight years ago but after hearing a few stories from the lady I'm leaning towards it being a DIY re-wire, probably done by her "builder" dad. I've certainly found a few bodges since starting.

Anyway what they have done is a 2 gang switch at the top of the stairs and a 2 gang switch in the hall so both the the landing and hall light are 2 way'd. Its loop in at the roses/fittings with a twin cable (L&SL) to the switch, exactly as you would expect to find it up to now. Separate 6A lighting circuits for up and down as well. Normally at this stage you would expect to find 2 x 3C&E cables between the switches but the way they have done it is 2 T&E cables for the strappers in L1 and L2 and for the common connection they have used another T&E, the brown in one switch and the blue in the other.

Now this method would be fine if it was all on the same circuit and I have done similar before, usually when I have looped in at the switches but how can I get over this one to make it compliant, she doesn't want the house tearing to bits and its mostly wooden floors upstairs as well. Maybe put all lights on the same MCB.

 

[James]

Although it is unusual, I cant think of a reg that it falls short of, providing the conductors are correctly sleeved.
and yes i understand that the 2 cores of the twin and Earth are from different circuits.

In some industrial applications it is not unusual for a 20 core cable to run several motors or heating zones all fed from different overcurrent devices, although the main isolator for the production line will often turn them all off, it is not always the case.

 

[7029 dave]

Imo, if you cant rewire to make intermediate (3 way dont exist) then make it one circuit.

 

[James]

if you just need to add an intermediate switch then you are only interested in the strappers, hopefully the cable passes near to the location of the new switch and all 4 cores you need are there, 2 in 2 out.

 

[7029 dave]

You could run a three core&earth from the nearest two way position make that your intermediate then what was the common wire join it up in the back of the box with the spare core in a connector/wago and at the new switch end strappers in L1 L2 common in common.
does not help the circuits in one cable or does it?

 

[westward10]

Two or more circuits are permitted in the same multicore cable your instance is different however. From my reading it does not adhere to Regulation 521.8.1.

 

[James]

I read it as 521.7 two or more circuits are allowed in the same cable providing the requirements of section 528 are met.

521.8.1
each part of a circuit shall be arranged such that the conductors are not distributed over different multicore cables, conduits, ducting systems or tray or ladder systems.

if you take that to the extreme, a normal lighting circuit ( loop at rose) would employ different multicore cables for distribution to roses and then switch drops and possible 2 way switching etc.

or am i missing something?
in my opinion we are trying to find fault with something that is unusual but safe and i cant see a contravention of regs.

 

[westward10]

Yes they would but the cores of that cable are part of that circuit. Slipping one into another cable which forms part of another circuit to me goes against that Regulation.

 

[James]

I am honestly not 100% sure on the interpretation either way.

521.8.1 doesn't mention other circuits, just that each part of a circuit should not be distributed over different cables, honestly i think it is poorly worded and difficult to adhere to in many circumstances.

I kind of think that it is to prevent large distribution circuits having problems with inductive heating of conduits from imbalance of the currents but I'm not sure.

however I cant see a safety issue with the op's multiple circuits down one multicore cable.

 

[pc1966]

521.8.1 doesn't mention other circuits, just that each part of a circuit should not be distributed over different cables, honestly i think it is poorly worded and difficult to adhere to in many circumstances.

It makes me feel uneasy as you could attempt to isolate one via the MCB and fine one of those cores is still live.

Still, this has pointed out the regulation applicable another of my friend's inherited WTF cabling specials - a 1/4hp 3P fan fed from 2 * 1mm T&E (not even 3&E that at least was used from functional switch to fan), with one that had just one of the 3 L, yet both CPC and the 'N' of that T&E left open. Creative you might say

 

[westward10]

You definitely cannot use two cables for a three phase circuit with the cores split over them.

 

[pc1966]

You definitely cannot use two cables for a three phase circuit with the cores split over them.

Indeed. I am awaiting the EICR she has commissioned, I expect there to be more C1/C2s than anything else.

 

[oscar21]

Just to update this thread, we've steered well clear of the original electrics and put our own little consumer unit in for our new work. The standard of their "re-wire" was appalling. There were things like the summer house/bar being fed from a 2.5 SWA drilled through the wall with a plug on the end shoved into a socket, when I took the top off all the wires fell out. They wanted the original downlights extending into the new bit but the way they were terminated was as bad as I've seen so we just put our own circuit in.

The customer didn't seem bothered at all so its obviously her "builder" dad that did it otherwise she would be looking for her money back I guess.

 

[7029 dave]

So how did you get round the proposed intermediate switching or did you just leave it 2 way.

 

[oscar21]

So how did you get round the proposed intermediate switching or did you just leave it 2 way.

We just left it as it was, again the customer didn't seem too bothered, dont think she wanted me digging any further.