Ring to Star electrical circuits and junction boxes

[JupiterJon]

As I need to rewire my new house I thought I'd take the opportunity to add some home automation ... however there are so many options and all the good ones (star network with DIN based switching) seem too expensive for me just now. So how difficult is it to convert from ring to star?

Would it be possible to:

-Run the ring to sockets and switches in conduit through plaster initially If / when budget, time etc allow use of c-bus or similar For a socket

-draw-out ring cable from conduit leading to socket

-use a junction box in under floor cavity to make ring continuous

-drop star-cable into socket For a light

- using existing ceiling rose / junction box in under floor cavity to continue light ring

- connect light fitting to star-wired DIN-Dimmer

- draw-out live/switched live cable to switch from conduit

- drop in c-bus control cable to switch box

I understand that in the recent regulations junction boxes are frowned on, but they must be used for lighting circuits and if running a garage circuit from a consumer unit (or are you expected to run SWA cable through the house too). So if these are acceptable is the above use of junction boxes OK???

TIA Jon

[Guy King]

The message from "JupiterJon" contains these words:

You can do lighting circuits without junction boxes. Often don't, of course, because it'd get silly trying to do the whole thing as a loop-in daisychain, but if you were sufficiently perverse...

[dcbwhaley]

Junction boxes must be 'accessable', a term which is as open to interpretation as the rest of regs. General opinion seems to be that a junction box under floor-boards, especially with fitted carpet or wood block is not accessable.

Apparently vibrations occur at mains frequency and this can cause the screws to loosen because electricians, unlike other engineers, haven't discovered self locking screws or screw locking compound yet :-)

[rrh]

Could we have a source for this please? If true it would have a dramatic impact.

[Guy King]

The message from "dcbwhaley" contains these words:

Braqss screws done up tight enough seem to work fine. When they squeak it's good and tight.

[gort]

What vibrations at mains frequency? Thats 50Hz!.

Dave

[gort]

Oh silly me. a Google groups poster1. Should have known.

[dcbwhaley]

Regulation 526-04-01 refers to accessability of junction blocks

An NICEIC recommendation says "However, connections required by regulation 526-04-01 to be sccessible should NOT generally be located under a floor where a carpet is likely to be laid. A fitted carpet can effectivley render connections beneath the floor inaccessible because of objections from the occupier to the carpet being lifted, or difficulties in finding the access trap."

But it does seem to be a widely ignored reccomendation.

[JupiterJon]

Ignored yes, I cannot see how to wire a light which doesn't have its own rose without it being concealed?

For sockets does this mean that if I used some big chocolate block at the back of the socket box and ran an additional star-wired cable down the conduit that would be OK? For a double 13A socket I assume 1.5mm cable would be fine?

Thanks jon

[Jerry]

Why would you need to use a 'choc-block' in the back of a socket box, why can't you use the socket terminals, or are you proposing to remove the existing face plate?

[John White]

It's tricky to convert power circuits properly. Also most of the systems I have seen or installed control very few socket outlets directly. You will almost certainly still need a number of uncontrolled sockets to plug in such things as a vacuum cleaner.

Where appliances are to be switched in this way it's much better to wire them using radial (star) circuits in the first place. You can initially connect them into appropriate MCBs at the consumer unit and add any control units later.

This allows you to wire the ring circuit in the usual way and to make all the usual load calculations.

Switches are not normally on a ring. You will also find that conduit does not fit in the depth of most plaster - so be prepared to dig into the walls as well.

Yes. However if such sockets were wired as radials anyway then you would only need to add a control unit at an appropriate place.

Why not run the cable for the light fitting and light switch to where you eventually intend to locate the DIN system boxes. You can then make all the connections there and it will save you pulling up the floor later.

I don't know who told you this but they are wrong.

Junction boxes can be used anywhere as long as they are appropriately rated, and the connections made correctly.

SWA cable does not fit into junction boxes in any case.

John

[John White]

526-04-01 relates to "Accessibility of connections" in general and not just junction boxes. Access to junction boxes is not normally required for testing and inspection (or for any other reason during the life of most installations), and I suggest that NICEIC's interpretation of the regulation is a little over the top for most cases.

Work that requires access to such a junction box will normally involve ripping up the floor anyway.

Well you could use one of these and put the new fitting over it.

if you cannot get access through the floor you can always cut a hole in the ceiling. There is usually a way if you think about it long enough.

You must put a warning label on the socket outlet or the socket box. Anybody removing the socket could assume that the terminal blocks belonged to the same circuit as the radial cable.

Using crimps and a proper crimp tool would, in my opinion, be a better option for joining the ring as they take up less space in the socket box.

That depends on several factors such as the cable length and the rating of its protecting MCB, to mention but two of them. Generally a larger size of cable (2.5mm to 6.0mm) would be used.

John

[JupiterJon]

Wire as star originally and then add controls - that is an excellent and simple solution :) Not sure why I didn't think of that :-s The hurdle now is to work out which sockets should be star-wired. For sockets I am thinking 1 socket near curtains for automated opening, 1 for AV equipment that would sit on standby. And more for lights.

Thanks Jon