Rewire lighting circuits with limited access

[7029 dave]

I don't think notches are allowed in the bottom of a joist.
But if you have an existing steel conduit system and aren't moving any points why would you need to?

Incidentally, why is this rewire necessary?

1950's might be just on the brink of VIR.

 

[zippy]

Are we talking full conduit system.? It might be worth having a few switches 'off and roses and try the pull test. Singles will be your clue.

I think so, as the one rose I looked inside was using electrical machine screws to secure its connection block to the ceiling, so I am guessing this goes into a conduit round end.

 

[Guest125]

It does not matter in this thread why it is needed. OP - have you had experience in 2 plate wiring before?

 

[zippy]

He is just guessing, and by the language used in the OP he is probably not familiar with the layout of such a conduit system.
Normally a buried conduit system like that will only have boxes at each light fitting with continuous conduits linking them and then a conduit from each light point to the switch.

Correct, guessing at this point as I need a closer look, just assumed that supply was to roses and switched live through switch so some connections must be elsewhere in jb's.

 

[zippy]

Have you tried pulling on any of the existing wiring,if not this is your first job before quoting

Once you decide if they pull,the main problem may come with getting the supply from down below (if there is no pull)
You get the supply to a convenient light or switch,the landing being the only open area may very well be the best place to get that supply to lights/switches both above and below that floor

I would hazard a guess this is a simple singles rewiring through existing conduits,wall chasing and laminates destruction may end up being just an extreme solution
Take more care than normal before pricing,be sure exactly what you will be pricing for and any problems you uncover before the start


more
Had a quick look in one rose and only 3 conduit wires connected,
How many actual pipes are at the light positions and switches

Not tried pulling yet, will try that on next visit and do a lot more recon!

 

[Guest125]

Correct, guessing at this point as I need a closer look, just assumed that supply was to roses and switched live through switch so some connections must be elsewhere in jb's.

If wired in singles, normally there would be no permanent (loop) feed at the roses. These would be at the switches instead.

 

[zippy]

cut holes in the ceiling, notch on the joist with a multicutter, patch up with bits of plasterboard and filler. if you have to.

Yep, was thinking maybe similar using nail plates over notches before patching. Finding conflicting info about notching below joists, some say ok, some say not ok.

 

[SJD]

Correct, guessing at this point as I need a closer look, just assumed that supply was to roses and switched live through switch so some connections must be elsewhere in jb's.

The last similar installation I worked on, the wiring was a little adhoc, in that sometimes live run from rose to rose, and sometimes run from switch to switch (it was a big house), while neutrals generally run from rose to rose. But there was not a single L or N junction that was not at either a rose or switch, i.e. there were no inaccessible connections.

 

[7029 dave]

This was quite common in conduit systems for lighting circuits.(loop in switches). N at the rose points.

 

[zippy]

Are we talking full conduit system.? It might be worth having a few switches 'off and roses and try the pull test. Singles will be your clue.

I am sure it is full conduit, seen lots of singles and some bulging of plaster by switches.

 

[SJD]

Yep, was thinking maybe similar using nail plates over notches before patching. Finding conflicting info about notching below joists, some say ok, some say not ok.

If I cut a 100mm hole - not over a joist, then I can get my right angle drill and battery into the void, and cut a hole in the middle of the joist - always assuming it is located in the right part of the span to meet building regs rules! One ceiling hole gets me holes in two joists.

 

[davesparks]

Yep, was thinking maybe similar using nail plates over notches before patching. Finding conflicting info about notching below joists, some say ok, some say not ok.

I think that falls under 'part A' so that would be a good place to look for the info

 

[Guest125]

http://niceic.com/Uploads/File3777.pdf

Havn't plumbers been notching joists forever?

 

[zippy]

I don't think notches are allowed in the bottom of a joist.
But if you have an existing steel conduit system and aren't moving any points why would you need to?

Incidentally, why is this rewire necessary?

Well was thinking it would not be that straightforward pulling new singles through all of that conduit and looping supply etc, so was looking to replace with t+e simple radial circuit. Customer wants it replacing, looks in bad condition, oh, and not all of it is in conduit ... seen some runs of singles around doorways, thought it was telephone first, but it was live lighting.

 

[zippy]

It does not matter in this thread why it is needed. OP - have you had experience in 2 plate wiring before?

Nope, none.

 

[Leesparkykent]

Well was thinking it would not be that straightforward pulling new singles through all of that conduit and looping supply etc, so was looking to replace with t+e simple radial circuit. Customer wants it replacing, looks in bad condition, oh, and not all of it is in conduit ... seen some runs of singles around doorways, thought it was telephone first, but it was live lighting.

Get that laminate up then mate, a decent chippy could take it up, number it like a jigsaw and be able to lay it back down again (prob could do it yourself if you can be arsed)

 

[zippy]

This was quite common in conduit systems for lighting circuits.(loop in switches). N at the rose points.

That would certainly explain the 3 wires to the one rose I checked. Would the loop in the switches be running up to ceiling in conduit and then taking separate conduit path to next switch as that would surely be almost impossible to pull without the access?

 

[ruston]

That puts a completely different perspective on it then, get the floorboards up and you only have one ceiling to worry about . Probably save you time in the long run.

Re post 36, Slow to get post sent. (dongle 3) not fast .

 

[Guest125]

Nope, none.

Look at 7029 Dave's diagram. That should help you understand why there probably is no JBs installed. A lot of sparks never see two plate so it seems alien but is very simple.

 

[davesparks]

I can't say I've ever heard it called 2 plate before.
There are two possibilities with a conduit system, the way Dave has shown above or the 'loop in' system which I described above