Neutral feed.

Postby Fellwalker » Mon Aug 11, 2008 9:27 pm

Recently, to correct a borrowed neutral problem, I've had to run a twin and earth from the new consumer unit to the loft to supply a neutral from one of the RCCB and MCBs to the ceiling rose of the stairs light. Now the downstairs lights and stairs lights work from one RCCB and the upstairs lights work from another RCCB. The problem never existed with the old crude fuse box!! My question: what is the best method of terminating or securing the live in the new cable? Can it be taped etc both ends?

I am only using the neutral and earth. The live is already in place from the existing cable, coming from downstairs via the switces and strappers etc. The old neutral (from the upstairs circuit has been isolated and securely taped).
Best regards to all, Paul
Posts: 9
Joined: Wed Jul 30, 2008 7:37 pm


Simply Build It

Postby ericmark » Tue Aug 12, 2008 10:43 am

There are a number of things to consider here.
As to spare core, this should be earthed, as both induction and capacitance within the cable can produce dangerous voltages if not.
Then 521.5.2 refers to passing through any steel holes both Line and Neutral must pass in same way to stop eddy currents.
If the Line and Neutral don’t follow the same route there can be EMC problems which may effect telephones etc. Both earths will need connecting because of:-
543.6.1 Where overcurrent protective devices are used for fault protection, the protective conductor shall be incorporated in the same wiring system as the live conductors or in their immediate proximity.
Remember a neutral is “Live” the phase wire in single phase supplies is called “Line” as both “Line” and “Neutral” are considered “Live”.
It seems this is becoming a common problem and it would be interesting to see if the overseeing bodies have any recommendations something grates as being wrong but can’t think what in back of my mind there is something about running feed and returns in same cable or conduit seem to remember something about hearing aides or something similar maybe one of the others will refresh my memory.

Postby Fellwalker » Tue Aug 12, 2008 5:09 pm

As I said the neutral is to complete the Double switched stairs(landing) light circuit. This was necessary after the installation of a new split load consumer unit. For safety reasons I wanted the d/stairs lights with langing light to be from one RCCB/MCB supply and the u/stairs lights to be from another RCCB/MCB.
The "professional" electrical contractors for the house building firm had connected the line/live core for the landing light from the downstairs lighting circuit, via the switches and strappers to the ceiling rose. They had then derived a neutral/live from the upstairs lighting circuit! Hence the need for my completing the downstairs circuit, with the neutral up to the landing light ceiling rose via my new cable. I always connect the earth cores both ends and sleeve them appropriately. In the new consumer unit all the earths for all circuits are connected to the same earth bar (Crabtree Starbreaker consumer unit).
Effectively I have completed the landing light cct from d/stairs, the neutral now supplied to the celing rose may be in a separate cable, but it is carefully routed and secured, with an earth from the consumer unit common earth. I understand now, in any case, it is preferred that neutrals are not connected or routed through lightswitch back boxes.
Best regards to you,
Posts: 9
Joined: Wed Jul 30, 2008 7:37 pm

Postby ericmark » Wed Aug 13, 2008 9:50 am

I would not think anything wrong in what you have done except for EMC (Interference) that may be caused if feed and return take different routes. For a light switch it goes to and from switch so no problem. The main problem in past is where instead of wiring two way switches with 3 core cable between switches the electrician has used two core and (Borrowed) the live from another circuit if no other items in the house nothing is seen to be wrong but as bluetooth, WiFi, etc. have become more wide spread then the EMC problems have become more pronounced but looking in the regs can.t find anything that says you must not do it. And I agree you need light and tripping is a problem I cured my house with an emergency light at the top of the stairs. And the fact you needed extra neutral seems to point to borrowed lives so you would have always had EMC problems you will not have made it any worse. Seems it affects some hearing aids. I would say don't worry about it unless you get some odd things happen to telephone etc. Then at least you will know where to look and if it has been laid on a similar route to live then unlikely to cause a problem.

Postby Fellwalker » Wed Aug 13, 2008 5:56 pm

Thanks Eric.
I described that the live came from the downstairs cct, via switches and strappers etc, the fact that they had used a neutral from the upstairs cct, I thought that this was termed a "borrowed" neutral. Do you agree?
The electricians never included a neutral from the downstairs cct to the ceiling rose, just picked one up from an upstairs lighting cct connection point.
No IT or comms equipment is affected in any way, and I have a lot of this equipment.
Still would like to know the neatest or best method of securing the unused live at consumer unit and upstairs lighting connection box ends.
Regards, Paul
Posts: 9
Joined: Wed Jul 30, 2008 7:37 pm

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