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wannabeaspark

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Called out today for an electrical fault.. Lights tripped and wouldn't reset (downstairs lights)
Checked consumer board and found mcb (non rcd) had been reset by client and no power in lighting circuit..
Quick check and no power to top of mcb.. diagnosise mcb blown..
Mcb blown means short circuit somewhere or overloading..
6 amp mcb to lighting circuit/s.. 2 cables.. running both upstairs and downstairs lighting circuits.
Consumer unit changed.friend of a friend etc.... spare 6 amp mcb next to lighting circuit..
No seperation of circuits?..more unanswered questions...
Dismantle cables to circuits. 2 line 2 neutral and 1 earth... another question
r1 and r2 of circuits.. getting readings of continuity downstairs.. both lines together and earth..
split lines to seperate circuits.... line 1 power & line 2 power.. End to end line to line continuous.. end to end neutral no reading.. .Diagnosise circuits are joined somewhere....
Kitchen light 3 feeds going in and 1 switch wire... lounge 2 dimmer switches/2 lights 400 amps ( signs of overheating to live feeds )..hallway fine. Upstairs landing 3 feeds and 1 switch wire..bedroom 1 ok... bedroom 1 not checked ( ceiling light and fan ) bedroom 2 not checked.... bedroom 3 ok.. visuals
Got to insulation resistance test all cables to see if there is a break in insulation...Once i can determine whats going where and what to.( dont want to fire 500v into somethinguntil i can diagnose cable runs and equipment)
Short of dismantling everything within the cable areas and testing Insulation resistance as a whole on both circuits, then breaking down into individual runs of cable when problems pop up... is there any other way to diagnose this problem?
 
You need to do an insulation test really, sounds like there might be a borrowed live on the circuit, possibly landing or hallway. Is it Twin and earth or conduit ? Maybe one lighting circuit has no earth?
Join l+N together and IR test.
 
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wannabeaspark

  • Thread Starter Thread Starter
  • #3
No it is twin and earth on both circuits.. but at moment can only find one earth.... not to say its not connecter blocked or something behind c u somewhere...Thats my next test and i still have to pin point if and where the low resistance is.....
Theres c p c in all the fittings and switches..
done a rough calcalation of the load and shouldn't be overload......then again not 100% yet where cables are going to and feeding what...
Thanks.. steve
 
turn all light switches off reset mcb and go through each switch till it trips ..........(then replace mcb) when fault found probably a loose burnt out ceiling rose
 
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wannabeaspark

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  • #7
didnt see the mcb blown already ..........lol ask her which was last new fitting that was put up
I've asked which if any lights have been replaced. and as normal got as least information as possible..
The mcb tripped as she walked in the kitchen ( the kitchen lights on a p i r )..After enquiring the mcb has tripped out a few times in the past ... All connections checked in lights/switchs downstairs and all fine...R1 and r2 all fine. Rn and r1 ok..
After replacing mcb with new one... switched on downstairs light (dimmer switch ) and the mcb tripped again... already had the switch apart and checked all connections beforehand...So thought i had pin pointed fault and reset mcb and went through turning all switches on again... Suprise suprise nothing starts tripping...
If it is a faulty light or switch surely that would activate mcb when fault occurs... Next step is to insulation resistance test the cables to see if they are ok...
The person who had changed the consumer unit obviously put the 2 lighting circuits into 1 mcb as there is obviously a link between the 2 circuits as there was a spare 6 amp mcb next to the blown one.. From what i can see and count up on the circuits it doesn't appear to be overloaded...
 
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MarkieSparkie

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  • #8
... lounge 2 dimmer switches/2 lights 400 amps ( signs of overheating to live feeds )...
If you really have a lighting load of 400A, signs of overheating and a blown MCB would be the least of your worries!
 
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wannabeaspark

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  • #9
I totally agree... 400 AMPS The blue sirens would have elimenated any problems so i wouldn't have been needed...
I'm new to this fault finding and just trying to work through methodically to find the solution...
2 dimmers rated at 400w... .. 5 x 60 watt lamps = 300w........ x2 == 600 w
1 kitchen light 4 x 50w gu10 = 200w
1 hall light... 60w say 100 for arguments sake =100w
1 landing light...100w
bed 1 ......100w
bed 2 ...100w
bed 3.... 100w
bathroom....... 100w
Loft lights........... 2x 100w=200w
Total = 6.5 amps.......... allowing for diversity............. 4.5 amps.....

Maybe the dimmer switches have gone faulty...scenario 1
Breakdown in the cable...scenario 2
Another feed to something else from circuit ....scenario 3
Faulty earth or neutral somewhere.scenario 4
Faulty switch/ light fitting...scenario 5.
 
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mackers

  • Thread Starter Thread Starter
  • #10
sure its not just a faulty mcb if no power to top side?
 
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Mark_Burgess

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  • #12
( dont want to fire 500v into somethinguntil i can diagnose cable runs and equipment)
Start off at 250 then.

Sounds like you need to remove all lamps and disconnect the dimmers and ceiling fans.

Also, the cable with the missing earth in the consumer unit, can you strip it back any more to get the tester on it or extend it with a wago?
 
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wannabeaspark

  • Thread Starter Thread Starter
  • #13
Thanks for all the advice............ .
When i was called out i was told the lights had tripped after walking into kitchen. (Kitchen light has a pir sensor )
when i turned up the mcb was on but no power and after check i found no power to top....... ( Faulty mcb maybe or blown )... I asked client how many times had tripped before and was told 3 or 4 times...
Replaced mcb with new one and switched on.. first light i checked( lounge dimmer ) tripped straight away, so reset and continued to check all others and no tripping.... weorked throught the house and then found nothing would trip mcb...
I've done r1 and r2 and rn and r2 through the whole circuit and found a non connected earth to 2 rooms, so reinstated that.. visual on all switches and light fittings.... all ok apart from signs of over heating on dimmer switches.......
Insulation tested at 250v l-n to cpc and tests all come back fine so believe the insulation is ok.. and continuity is ok...
Changed the dimmer switch and now everything seems to be fine.....
A good learning curve for a faulty dimmer switch it seems..
 
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wannabeaspark

  • Thread Starter Thread Starter
  • #14
Plus i found the missing earth on the other side of the bar....
 
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Engineer54

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  • #15
Changed the dimmer switch and now everything seems to be fine.....
A good learning curve for a faulty dimmer switch it seems..
It just may have been the faulty MCB blowing apart internally, that damaged the dimmer switch!!! They are not the most robust devices at the best of times. ... I hate using the things lol!!!
 
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