Is this a common house wiring fault?

zax47

ValHaller wrote: »

So you have individual RCD's for upstairs and downstairs lights? This would be unusual. Or do you mean RCBO's?

Not unusual at all - recommended/preferred design rules, see my post above.

ValHaller

fwor wrote: »

No, a 17th Ed split load consumer unit with an RCD on each "half". I'm led to believe that where possible it's advisable to split lighting circuits across both "halves" so that if either trips you still have some lighting.

But that can't be done in this situation.

I believe that the requirement you are alluding to is

314.1 Every installation shall be divided into circuits, as necessary to:

• avoid hazards and minimize inconvenience in the event of a fault
• ....
• take account of danger that may arise from the failure of a single circuit such as a lighting circuit
• ....
• ....
• ....

In your position I would be taking the line that until such time as I could separate hall and landing lights to a circuit of their own, the lighting would have to be on one side of the board only. Strictly, if the lighting is 2 circuits, you do have a non compliance for borrowed neutrals.

And I might rig up some other lighting for the consumer unit area on the other side of the board, ideally with as little other load on that side as possible.

I don't know how others have done it, I have never done a split load board, but I have always put hall and landing lights on their own circuit and had separate upstairs and downstairs circuits. This means that if just one circuit goes, you are always next to a room with light. On a split board, I would put the hall and landing circuit away from the rest of the lighting.

A solution, if you have a reasonable pull from the consumer unit to the loft is to use the existing lighting feed to the loft to pull up 2 cables - 1 as a replacement upstairs lighting circuit and another as a downstairs for the hall and landing. which should be good enough to address the borrowed neutral.

As and when you get access, you could repeat for the downstairs circuits.

fwor

ValHaller wrote: »

And I might rig up some other lighting for the consumer unit area on the other side of the board, ideally with as little other load on that side as possible.

By coincidence rather than design the consumer unit is in the attached garage, and the lighting in the garage is supplied from the other side of the board, so I'm covered on that.

But I take your point about the borrowed neutral being non-compliant.

I'll take a look in the loft but the light fitting is under loft boarding and the route from CU to loft goes through the wall and then does a right angle (the board is effectively on the outside wall of the house) so it's never going to be easy...

Thanks to all for the advice.

ValHaller

fwor wrote: »

I'll take a look in the loft but the light fitting is under loft boarding and the route from CU to loft goes through the wall and then does a right angle (the board is effectively on the outside wall of the house) so it's never going to be easy...

Thanks to all for the advice.

If you have access to the top of the cavity and the existing upstairs cable enters the loft reasonably vertically above the consumer unit entry to the cavity, this will probably work as a 2 man pull - particularly if you can drop say some lighting chain down and catch it with an old steel tape measure looped into the cavity.

ValHaller

zax47 wrote: »

Not unusual at all - recommended/preferred design rules, see my post above.

OP did not explicitly mention split load board and seemed to imply that the consumer unit was an existing item hence I was trying to clarify what was going on before jumping in with a solution