3

When switching on a light the circuit breaker tripped.

On the distribution board, I switched off the sub-circuit for the light. The rest of the house and the plugs in the room with the light still have electricity.

I removed the entire light fitting from the ceiling. Then there where 2 wires poking through the ceiling. One wire is red, the other wire was black. (I assume red is live and black is neutral.) I cut off the black wire because some of the insulation had come off. (I cut off the black wire from the point where it branched from another black wire which goes to another light.) Now only the red wire is poking through the ceiling.

The entire ceiling (not the roof), is made of thin pressed metal plates (yes metal, not fibreglass). One side of the ceiling is painted (i.e. the side inside the house). The side of ceiling in the attic is not painted. At the spot on the ceiling where the light fitting was, some of the paint has come off. When touching the exposed end of the red wire to the unpainted ceiling, the circuit breaker trips.

I assume somewhere in the attic a black wire (from another light fitting, or from the cables leading down to a plug) is touching the metal ceiling.

The attic is a mess. It is impossible to walk in the attic due to the struts, rafters, beams, braces (i.e. all the wood holding up the roof). I can only "crab-along" the horizontal beams that rest on the walls. Of course I cannot step onto the pressed ceiling; it is far too thin. Pink insulation wool is lying on the pressed ceiling. The black and red cables run above the insulation wool. The black and red cables run from the distribution box, in parallel, seperated by about 3cm, until they descend down into either a light fitting or down towards the plugs. I have also noticed what seems to be earth wires. These are uninsulated metal cables. These earth cables frequently run under the insulation wool. As far as I can tell, the earth wires touch the ceiling.

To narrow down the cause, I switched off all sub-circuits on the distribution board. Then, one-by-one I switched on each sub-circuit individually, and tried to cause the short circuit. Only 2 sub circuits cause the problem. These 2 circuits are for the plugs in various rooms in the house.

Questions

  1. How do I track this short circuit down ? My plan was to lift the insulation wool and to
    • check that all red and black cables are still insulated
    • check for any exposed red or black cable touching the ceiling or the earth cables.
  2. Is there any device that can help me track this problem down?
  3. For safety, before going up into the attic, I will switch off the electricity to the house (at the entrance to the property). Or is it safe to only switch off the 2 sub circuits causing the short circuit and the sub circuit for the light (which will then allow me to take an electric light up into the attic - otherwise I will need to use a flashlight)?

    (Other info: South Africa, 200V, 50Hz, very old house with very old wiring, I think from the 1960s)

1

I use the Greenlee 77M-G tone generator and the Fluke Network Pro 3000 Tone and Probe Kit.

1

My goodness thats quite the day you have going on. I do not know South African Voltages and the way your systems work down there, but it sounds like you are shorting the wires out when you are taking a "hot" wire and touching it to your metal ceiling (which sounds to be grounded from the un insulated earth cables running along the metal cladding).

I am wondering if, when you are trying to short wires out, you are actually using hot wires. I feel like maybe some of the wires you are trying to short out might not actually be hot (Here is canada not all boxes have hot wires, but instead in lights it can be wires that are hot when the switch is on/closed).....So perhaps you were using not hot all the time wires. You would need to use a meter to see if it was a hot wire.

I am not sure if anything is really wrong here except maybe that wire you found with the insulation off was giving you problems...

But please know that I DO NOT understand this question fully or understand your power situation in South Africa but you seem nice so I thought I would try....

Keep us informed.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.