Fault on lighting circuit | Page 2 | on ElectriciansForums

Discuss Fault on lighting circuit in the UK Electrical Forum area at ElectriciansForums.net

Bear with me because this is long. So got an intermittent fault on the upstairs lights. Trips the mcb after a few hours, getting a reading of 0.01 mega ohms between live and earth at the board, tested cable going to db from first switch and it’s clear. Tested the cable going from first switch to rest of switches and getting a reading of 5.2 megaohms so can’t understand where the 0.01 is coming from as I wired it so know there isn’t any joins. Also the cable going from first switch to rest of switches loses its earth, so I think the cable is obviously damaged but can’t understand why this isn’t showing when I test and why it’s tripping intermittently. Maybe I’m missing something completely obvious
Is there 2 faults here or if the cpc between db and first switch was clear between l,n,e and not damaged and earth continuity verified then cpc further down the line might be restored .or have I misunderstood your wiring description
 
Is there 2 faults here or if the cpc between db and first switch was clear between l,n,e and not damaged then cpc further down the line might be restored .or have I misunderstood your wiring description
So there is 2 faults but I don’t know if they are linked. Basically losing the CPC between switch 1 and 2. But not sure if this is what’s causing the tripping as the cable must be damaged
 
Possibly:

Your IR tests carried out downstream of the first switch are between line and the floating CPC, that is not connected to the earthing system.

However, the fault may not be between line and that floating CPC. It may actually be between line and some other part of the building that does have a tenuous connection to the earthing system. Hence why you get low IR L-E tested at the board (where the CPC is connected to the MET), but not downstream of that first switch.

Try: Connect your wander lead to the MET, and take that with you to a point downstream of the first switch, and do your IR test between L and the wander lead. I suspect you will now get a low IR reading.

Had a similar fault yesterday. Low IR 0.08 N-E, but the CPC had become disconnected somewhere. Once the CPC was reconnected, it was a dead short of a fraction of an ohm.
I will try this when I’m next on the job, thanks for the help.
 
No it’s not. He asked what reading I got when I tested on low resistance ohms so wasn’t megaohms. So maybe it’s yourself that needs to know the facts beforehand
Like I said, don't take offense.
I'm just speaking factually.
You said 'I think' I got, therefore I'm just asking for accurate figures.
It would be very surprising to get a reading almost exactly 100 times smaller than the IR reading. It's more likely that you got 10000 ohms.
 
Like I said, don't take offense.
I'm just speaking factually.
You said 'I think' I got, therefore I'm just asking for accurate figures.
It would be very surprising to get a reading almost exactly 100 times smaller than the IR reading. It's more likely that you got 10000 ohms.
I definitely didn’t get 10000 ohms
 

Reply to Fault on lighting circuit in the UK Electrical Forum area at ElectriciansForums.net

News and Offers from Sponsors

  • Article
Join us at electronica 2024 in Munich! Since 1964, electronica has been the premier event for technology enthusiasts and industry professionals...
    • Like
Replies
0
Views
628
  • Sticky
  • Article
Good to know thanks, one can never have enough places to source parts from!
Replies
4
Views
1K
  • Article
OFFICIAL SPONSORS These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then...
Replies
0
Views
2K

Similar threads

  • Question
I would add though that a typical good TT rod of 100 ohms only needs 3V to have 30mA flowing and so trip an RCD, you might find that sort of N-E...
Replies
8
Views
727
Exactly. I was going to ask on the earthing once he clears this boiler fault (suspect on internal component). OP mentions oil boiler but makes no...
2
Replies
19
Views
743

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

YOUR Unread Posts

This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
Back
Top