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Failure on IR

RustyH
Evening All,


I’ve been running over some pre-existing circuits, unfortunately for a mate so I’m not even getting paid!!, and all circuits have passed accept one that I just cannot figure out.

It’s a standard 2.5 ring circuit for the lower sockets (only feeding a lounge area), supply comes out the CU, up through the first floor rafters, and drop to the first and last sockets. All other joining wires between sockets run under the floor boards (House has concrete floor in kitchen and hall, but wooden floor in the lounge).

Running IR tests, no issues at 250v, but then at 500v it ramps from 280 m ohms till it reaches 500, then at 1000 same scenario, starts at 280 m ohms and ramps up but never really makes it to the full 1000 m ohms. It seems worse on the L-E, but does also fail on Lives.

I’ve tried to fault find this by removing the sockets, testing individual cables (which all seem to pass), and then shortening the ring one socket at a time by use of a plug in link and disconnecting the sockets beyond the link. The conclusion I believe I have come to is that the two feed lines from the CU (by linking the first and last socket and removing the rest of the circuit out of the ring) are passing IR without any ramp up. The minute I start adding in the rest of the circuit, it begins to fail, so I’m sure there are issues with all the circuit under the lounge floor.


I am assuming it’s all 2.5 T+E under there, there is a spur which doesn’t seem to link to a socket (feed a light switch to an outside light), so hazard a guess is linked to a junction box under the floor.

With it being a ramp up on IR values, could this be a moisture issue? Maybe a cable is laying on the floor under the house and drawing moisture?

Or could it being a rodent issue maybe?


Any experience on this one and advice would be appreciated


Thanks

Rusty

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    I remember seeing it talked about on the old forums and the mention of moisture. That why it was going through my mind that that could be the reason. 


    no new plastering works, no sign of damp on walls. 

    With cabling being under the floor boards of ground floor, Cables may have not have been attached to joists properly and resting on the ground (probably old bricks and crap from when the house was built). Looks a old house, late 60s, so might have no damp proof on the ground under the floor board. If a cable is resting on cold damp floor, could that introduce moisture in to the system.


    I don’t see anywhere in the regs that say you can’t route cables in the void under floors at ground Level, but is there not a heightened risk under there of rodent damage or moisture?
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  • 0
    I remember seeing it talked about on the old forums and the mention of moisture. That why it was going through my mind that that could be the reason. 


    no new plastering works, no sign of damp on walls. 

    With cabling being under the floor boards of ground floor, Cables may have not have been attached to joists properly and resting on the ground (probably old bricks and crap from when the house was built). Looks a old house, late 60s, so might have no damp proof on the ground under the floor board. If a cable is resting on cold damp floor, could that introduce moisture in to the system.


    I don’t see anywhere in the regs that say you can’t route cables in the void under floors at ground Level, but is there not a heightened risk under there of rodent damage or moisture?
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