Old three-way light circuit wiring

[Deleted member 102649]

A little advice from a sage, please.
In the dormer bungalow we're renovating there is a three-way switched light for the upstairs landing, one switch in the hall, one (an intermediate) at the bottom of the stairs and one on the landing.
A lot of the wiring is well buried behind render/plaster, under floors, roof spaces, etc.
All back boxes are metal and earthed.
The bits of cable behind plaster appear to have plastic capping put on before it was rendered/plastered. Certainly the case where the plaster fell off elsewhere!!
The supply to the circuit appears to come from a junction box in the eaves, which I can get at quite easily.
I can see another junction box (looking under floorboards) which appears to be the link for the wiring running to and from the intermediate, as if the intermediate was a bit of an afterthought.
The common terminal on the hall and landing (outer) switches have a single conductor connected to them.
Neither of the 'outer' switches has two wires into any terminal
Neither of the two 'outer' switches have two wires into any of the terminals.
The intermediate has two runs of twin and earth only, ie, I assume it has no 'common' running through it tying in with my 'afterthought' idea.
I'm fairly sure I understand how it all works, I guess it is a fairly old setup (house built mid-70's) and it's a major digging job to change it.
Maybe worth saying it all works OK.
My questions are:
Is it likely to be unsafe, even though it looks tidy and quite well installed, properly earthed, etc?
What are the down sides of the setup?
I assume it's advisable (necessary, from a safety point of view) to swap the junction box that contains links for the intermediate from a screwed to a maintenance-free box?

 

[telectrix]

i would imagine it's the alternative wiring method, usually nowadays only done when using singles. L into switch #1 common, pair of strappers through int. sw. to switch #2, L1 & L2, switched L from switch #2 common to light.

 

[Deleted member 102649]

I read somewhere that it's now only used in industrial 'conduit' type circuits.
My main question is, though:
Even if it ain't a preferred method anymore, is it unsafe?

 

[telectrix]

nowt wrong with it if it is installed properly. it was used when 3 core/E was not readily available. the problem you may have is when the L is fed from the downstairs lighting circuit, and the N from the upstairs. commonly called a shared neutral. which is incorrect imo, as it's the L that is shared. this was common in the 60's and early 70's.

 

[Deleted member 102649]

Funnily enough................
I happen to know for sure that the neutrals for all the downstairs lights - which that circuit is on - are from the same neutral. They weren't but were sorted out by a professional lecky when questions arose regarding RCBOs. His apprentice(?) had the pleasure of going in the loft and squeezing past the water tank/under the insulation to sort it. Felt quite sorry for the poor bu**er
Result, though!
Many thanks for the info, telectrix. I thought it looked clean, tidy and safe enough and even if a bit odd/minimal, couldn't see anything obviously bad about it - but I ain't a professional.
You've saved me quite a bit of work/worry/mess.
Thanks again.
Will

 

[Des 56]

What could be described as the "old" method was and is the original standard way to wire a 2 way and intermediate circuit
The alternative (using a 3 core) with a common running through the intermediate used to be described as the conversion method

 

[Simon Rutherford]

i have just used this meathod my-self, a previous live to a new junction box i.e next circuit to permant live or common on master switch then L1>L1 L2>L2 conecting the two switches together and the switched live or common from the slave switch back to the junction box to feed the lighting circuit. this has worked with no incident or disruption to the lighting main. i am not a sparky by trade but am involed in electronics

 

[Simon Rutherford]

when i say previous live i do meen live and neutral of course.

 

[telectrix]

either method, as long as done to regs. and left in a safe condition, is OK. only jibe might be screwed terminal boxes inaccessible, but these exist in thousands of homes, never giving rise to problems. a screw terminal box, if installed correctly will probably outlast some of these fancy so-called MF jobbies.
on a slightly different tack, just been on a call-out this morning. bit of green goo seeping from a 2 way switch ( 1960's build). quick clean, re-terminate cables into new switch ( existing one was cracked and terminals were black). cable is 3/029 (stranded), what a pleasure to work with compared to the solid shyte we have to use today.

 

[Simon Rutherford]

Thanks telectrix. it is now hidden behind plaster board, in the ceilling and yes there is that patential.