sparkytim
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Hi Guys
Had an interesting week of fault finding thought might be of interest to some,
1 Farm house Lighting circuit 20 year payback.
Called out by customer to this Farmhouse, MCB on lighting circuit tripping out intermittantly.
Fault History;
About a week earlier owner realised Lights not working in some parts of the house, found 6A MCB tripped (non RCD protected)
Reset looked around for lamps gone, all working OK.
Next day same thing, this time on resetting MCB it tripped out 10 Mins later, reset this time its ok for a day or two then same again.
Investigation;
Take cover off C Unit (Split load to 16th Edition), see two conductors from the MCB concerned, remove both and associated Nuetrals and Test first continuity, L-N, L-E, N-E. One circuit all OK as normal (Low reading L-N, L-E, N-E , High (+99.9 ohms)
Other circuit N-E and L-E 50 ohm fault
Diagnosis N-E + L-E FAULT ?.
Insulation test on same indicates also Low insulation L-E + N-E ( 0 M ohm) as it would.
Locating fault;
Reconnected GOOD circuit and switch back on MCB, go around house and turn on all lights, this identified which areas could be ignored and which were potential fault location, found that faulty circuit affected ALL downstairs and Landing light.
Leaving all lights ON, have a cup of Coffee.
As I was drinking it and chatting with customer, "CLICK" MCB goes out, "Errr". First doubting myself, think Idiot will have to start again.
But just to make sure have a look around and notice in the bathroom one of the 50 Watt GU 10s that had been left on is out, check with customer "It was all ok earlier", so how about that Mr coincidence strikes again!. Could have easily thought that was the original fault and been totally thrown.
So gets back to the hunt, find junction box in loft where circuit splits in to 4 and split off, retest at CU Fault gone, Test at JB leave faulty spur dis and reconnect others connect up at CU and turn on, left with Landing and Hallway lights NOT working so now have target area.
Now this is where things get interesting, still getting 50 Ohm fault, by this time I had recruited customer to Meter watch and shout when anything changed,
Remove landing light lamp and hey presto 50 ohm fault disappears, just to be sure switch Meter to Insulation test and 50 K Ohm fault L-E but N-E fault Gone.
Hummmm 50 ohm was the lamp, but why to earth? Landing light common set up ? BORROWED NUETRAL. trace it out and yes N comes from another JB on the other circuit, so the 50 ohms had been thru the lamp and back to E via the other circuit N. Swopped it over to the correct JB.
Now heres a lesson, faults are not always just a single problem and one fault can hide or affect another.
So what now, well retesting the hall and landing cable showed a L-E fault on ONE LEG of the two way strapper from the downstairs switch to the upstairs, floor board up on the landing, find cable cut it, test down to switch all ok, test UP to landing switch, L-E low insulation on one leg.
Cable under capping up the wall, try and pull it up, no good, so open up hole in wall just above skirting, hook cable and yank up from below floor and up it comes complete with capping NAIL right thru it.
Its a great feeling to actually SEE the fault right there before your eyes, and yes we worked out it had been there 20+ YEARS!, (Before my time on this property) Fault had gradually broken down enough to trip MCB after all that time, but ONLY when two way switch downstairs was in ONE of the two possible positions, hence its intermittant fault history.
Rewired damaged cable, re connected and re tested circuit, had a cup of tea and headed for home.
Have another couple to share a bit later.
Had an interesting week of fault finding thought might be of interest to some,
1 Farm house Lighting circuit 20 year payback.
Called out by customer to this Farmhouse, MCB on lighting circuit tripping out intermittantly.
Fault History;
About a week earlier owner realised Lights not working in some parts of the house, found 6A MCB tripped (non RCD protected)
Reset looked around for lamps gone, all working OK.
Next day same thing, this time on resetting MCB it tripped out 10 Mins later, reset this time its ok for a day or two then same again.
Investigation;
Take cover off C Unit (Split load to 16th Edition), see two conductors from the MCB concerned, remove both and associated Nuetrals and Test first continuity, L-N, L-E, N-E. One circuit all OK as normal (Low reading L-N, L-E, N-E , High (+99.9 ohms)
Other circuit N-E and L-E 50 ohm fault
Diagnosis N-E + L-E FAULT ?.
Insulation test on same indicates also Low insulation L-E + N-E ( 0 M ohm) as it would.
Locating fault;
Reconnected GOOD circuit and switch back on MCB, go around house and turn on all lights, this identified which areas could be ignored and which were potential fault location, found that faulty circuit affected ALL downstairs and Landing light.
Leaving all lights ON, have a cup of Coffee.
As I was drinking it and chatting with customer, "CLICK" MCB goes out, "Errr". First doubting myself, think Idiot will have to start again.
But just to make sure have a look around and notice in the bathroom one of the 50 Watt GU 10s that had been left on is out, check with customer "It was all ok earlier", so how about that Mr coincidence strikes again!. Could have easily thought that was the original fault and been totally thrown.
So gets back to the hunt, find junction box in loft where circuit splits in to 4 and split off, retest at CU Fault gone, Test at JB leave faulty spur dis and reconnect others connect up at CU and turn on, left with Landing and Hallway lights NOT working so now have target area.
Now this is where things get interesting, still getting 50 Ohm fault, by this time I had recruited customer to Meter watch and shout when anything changed,
Remove landing light lamp and hey presto 50 ohm fault disappears, just to be sure switch Meter to Insulation test and 50 K Ohm fault L-E but N-E fault Gone.
Hummmm 50 ohm was the lamp, but why to earth? Landing light common set up ? BORROWED NUETRAL. trace it out and yes N comes from another JB on the other circuit, so the 50 ohms had been thru the lamp and back to E via the other circuit N. Swopped it over to the correct JB.
Now heres a lesson, faults are not always just a single problem and one fault can hide or affect another.
So what now, well retesting the hall and landing cable showed a L-E fault on ONE LEG of the two way strapper from the downstairs switch to the upstairs, floor board up on the landing, find cable cut it, test down to switch all ok, test UP to landing switch, L-E low insulation on one leg.
Cable under capping up the wall, try and pull it up, no good, so open up hole in wall just above skirting, hook cable and yank up from below floor and up it comes complete with capping NAIL right thru it.
Its a great feeling to actually SEE the fault right there before your eyes, and yes we worked out it had been there 20+ YEARS!, (Before my time on this property) Fault had gradually broken down enough to trip MCB after all that time, but ONLY when two way switch downstairs was in ONE of the two possible positions, hence its intermittant fault history.
Rewired damaged cable, re connected and re tested circuit, had a cup of tea and headed for home.
Have another couple to share a bit later.
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