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Discuss First eicr and low iR readings in the Electrical Forum area at ElectriciansForums.net

Baddegg

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Being new to this game I’ve been waiting a while for the right job to come along and I have now done my first eicr today, small Chinese takeaway 2 circuits (lights and 1 rfc) most cooking appliances are gas, found some interesting stuff like sockets wired from lighting circuit,main bond buried in concrete floor amongst other things...anyway place is not trading at moment and this is due to sale of the business so I managed (I think) to unplug everything it is oldish and I was expecting some low ir results but,...L-N 0.537 N-E 0.076 L-E 0.2....tested my tester on a piece of 10mm cable before and after and they are fine, so other than something being connected I can’t understand why they are so low, rcd tests fine (newish board). Not fussed at filling the report out and stating the findings just my curious nature needs to understand if it’s normal to be that low and suffer no side affects.....
Ps lighting circuit tests at 1.135 L&N to E due to being unable to remove most of the lamps..
 
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Forget line to neutral readings. Any rcd sockets or spurs. What type of cabling is it.
 

Baddegg

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Are you sure you removed ALL loads including neons, PIRs, lamps, etc. If you cannot be certain test between L&N together and cpc.
Thanks for replying @SparkyAndGeorge, I turned the place upside down, I gave myself a whole day to do this as I wanted to take my time and not be rushed, I did initially test L&N together and the readings were still sub 1 ohm, my head tells me there has to be something connected but I can’t find it....
 

freddo

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The L-E and N-E readings are quite different which suggests everything could be unplugged. I'd now be looking for damaged wiring or waterlogged sockets etc. Splitting the ring in the middle will help narrow things down.
 

Baddegg

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Thanks @weatward definitely no rcd sockets, it’s a mixture of pre 2005 and newish t&e, it’s a really basic layout the board is a split board 1 half (2 circuits) covers the shop and the other half 2 circuits cover the flat upstairs I can only assume something is connected ( the owner tells me his son changed the Cu) as I say I’m happy to just give him the report as is I e been paid but I do like to understand these things...
 

Lucien Nunes

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N-E 0.076
0.076... Megohms? (please always use the unit even when you think it's obvious!)

That's unusually low and indicative of a problem, such as water in an fitting or JB, a rat-damaged cable missing a section of insulation, etc. Cold, damp circuits in unoccupied properties develop low IR due to the moisture film that builds up in the fittings, and this often explains readings of 0.5MΩ and up. But 76kΩ stands out as a fault.

I did initially test L&N together and the readings were still sub 1 ohm
1Ω? Or 1MΩ? Different prognosis depending on which you mean.
 

Baddegg

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The L-E and N-E readings are quite different which suggests everything could be unplugged. I'd now be looking for damaged wiring or waterlogged sockets etc. Splitting the ring in the middle will help narrow things down.
Thanks Freddo hoping I gets chance to investigate further er
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0.076... Megohms? (please always use the unit even when you think it's obvious!)

That's unusually low and indicative of a problem, such as water in an fitting or JB, a rat-damaged cable missing a section of insulation, etc. Cold, damp circuits in unoccupied properties develop low IR due to the moisture film that builds up in the fittings, and this often explains readings of 0.5MΩ and up. But 76kΩ stands out as a fault.



1Ω? Or 1MΩ? Different prognosis depending on which you mean.
Apologies Lucien....1M ohm where is that symbol?
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@Lucien Nunes it has been empty for a while so maybe damp/cold....
 

Lucien Nunes

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As Freddo points out, the fact that L-E and N-E are different suggests there is no load connected, otherwise its relatively low resistance would tend to cause both to be tested in parallel whichever lead you apply the test to, and give similar readings.

One aspect of low IR is that even if the cause isn't dangerous in its own right, it can lead you to a location where something more serious is waiting to be discovered.

My money is on rodents.

Ω: Switch your keyboard to Greek and type a capital V!
 

Baddegg

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As Freddo points out, the fact that L-E and N-E are different suggests there is no load connected, otherwise its relatively low resistance would tend to cause both to be tested in parallel whichever lead you apply the test to, and give similar readings.

One aspect of low IR is that even if the cause isn't dangerous in its own right, it can lead you to a location where something more serious is waiting to be discovered.

My money is on rodents.

Ω: Switch your keyboard to Greek and type a capital V!
Thanks lucien....they’ll sort the rodent problem when they re open I expect 😂
 
I'm sure you know that such a low reading is a definite C2, therefore an unsatisfactory outcome on the EICR. Best way to find it is to split ring into sections, and narrow down the location. I recently had a similar result caused by damp affecting several newish sockets and fcus on one particular wall.
 

Wilko

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Hi - the heating system (with its pumps and motorised valves) is always suspect to me and easily removed from play with the DP FCU. Try testing at 250V (L+N to E) as there may be surge suppressors somewhere getting lively. If you’ve time and out of interest I’d whip the fronts off all the outlets and see if that changes anything. If this is the place from the other post, I recall from the cutout pic it had heat affected tails, so there might be further carbonised insulation...
 

Baddegg

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Hi - the heating system (with its pumps and motorised valves) is always suspect to me and easily removed from play with the DP FCU. Try testing at 250V (L+N to E) as there may be surge suppressors somewhere getting lively. If you’ve time and out of interest I’d whip the fronts off all the outlets and see if that changes anything. If this is the place from the other post, I recall from the cutout pic it had heat affected tails, so there might be further carbonised insulation...
Thanks wilko, gave my self plenty of time,all day in fact, and took off every to the best of my knowledge socket front, yes same place as the other thread and the cpcs on the older (pre 2005) wiring are all blackened/carbonised
 
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Lucien Nunes

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the cpcs on the older (pre 2005) wiring are all blackened/carbonised
Blackened?! Any pics? Not familar with that at all. Is the whole place full of oily soot from wok fires or what? That could be a significant factor in low insulation.
 

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