Strange or old

[DPG]

Why change. If it's installed correctly and cable is good, the odds are it'll be OK for another fifty.....

I know what you mean, but to be honest it looks shocking. The way they've done it is loads of live/earth all spidering out from this junction box.

 

[Luke105]

Well thanks guys I have worked it out and have an understanding of it now.

 

[Lucien Nunes]

When wiring lighting with insulated and sheathed singles, there is a tendency to form induction loops as the line and neutral take different routes around the building. This doesn't happen with most T+E as the current in one conductor (e.g. L) balances that in the other (e.g. SL or N), nor with conduit as although the L & N loop in different fittings, they usually return with their partner to the same trunk route.

Compare 'conventional' 2-way, where current flows to one switch, to the other switch via the strappers, and back to the ceiling rose, creating a large window area within the loop, with 'conversion' 2-way where it flows to one switch, the other switch, back to the first switch and back to the rose i.e. always returning along the same physical route and confining the area of the loop to within the width of the T+E.

Induction loops radiate intereference from whatever current is flowing round them. Before CFLs and LEDs, this was just pure 50Hz, but now with SMPSUs in LED lamps with perhaps rather skimpy filtering, there is a wider spectrum of RFI that the loop might radiate.

Does anyone now avoid wiring in singles not confined to conduit, conventional 2-way, and other unbalanced cable runs specifically because of this?

 

[James]

Lucien, you have a good point.
There is a requirement to design installations so as not to produce excessive emi
Food for thought.