Tragic IR fail on EICR

[putalightuponce]

Hello all,
I could use some help here:
I was recently asked to do an EICR at a small warehouse/office unit.
The installation was, to put it mildly, less than satisfactory; with multiple C1 and C2 conditions. However, of greatest concern to me were the insulation resistance readings I was getting. I left the job, trying to explain the severity of the condition to the client, but still feel under the circumstances, he is unlikely to take any further action, despite his report been top to bottom in 'further investigation's.
Whereas I'm sure everybody on here has had this at some point (if not daily), it is the specifically the IR fails I am still scratching my head over.
2xsockets in floor boxes, 3xsockets in dado trunking, 3xlighting circuits, and 2xhand dryer spurs were all returning 0Mohms IR L-E, yet none of the associated breakers were tripping or had been problematic in any way. Breakers and board were old (maybe late 70s early 80s), no markings on breakers except obvious ratings, but I'm assuming wiring can't have been of same period unless floor boxes and dado trunking wre popular back then?? The decor and fittings were certainly more recent.
I was pleasently suprised to find a single A4 schedule of circuits reinforced with several layers of tipex and the board had a Ze and PFC reading written in it from 2002, but that was it for records.

Any thoughts???

 

[Breeze]

Did you test IR at 250v and 500v or 500v only?
if so we're the both 0Mohms?
if not it could be the insulation breaking down, water ingress somewhere, an appliance hidden somewhere

 

[Doomed]

you had disconnected lights properly? Neons in switches?

 

[alanl]

If you are getting a 0Mohm reading, then you then need to do a Low Ohm reading to find out exactly what the resistance is between the conductors.
With some experience, you can then take an educated guess as to what the link is between the 2 conductors - a neon, a PIR switch, a lamp etc.
If it is 0 ohms, then it will be a dead short, but you are getting a reading of less than a million ohms, so could be pretty much anything connected, or maybe nothing between the conductors (insulation breakdown).
Depending on your meters accuracy, the reading could be as high as 999,999 ohms, so further testing is required to find , or indicate, the true reading and cause.

 

[Deleted member 9648]

It's not going to be 0 mohm L-E in reality,because if it was the OCPD would operate assuming it is of the correct rating. More likely it is N-E and you are getting the reading through connected loads.
Did you test the circuits with both L and N of each circuit disconnected from the DB? If so are you certain the correct N was disconnected with the associated live?
It's very common for neutrals to be almost impossible to ID for each circuit if they are not in the correct order in a crammed DB without major disturbance,a mistake in identifying the correct N for a circuit will result in low IR readings if the correct N is not disconnected. Another common complication is more than one N for a circuit in different terminals,with the same result.
If it is apparent that neutrals cant easily be ID'd for disconnection an option to verify satisfactory IR is a global test with the incoming N isolated from the DB. Some frown on this method but they tend to be people who sit at keyboards passing judgement having never actually carried out an EICR in a real working environment.

 

[Deleted member 9648]

deleted

 

[davesparks]

What is tragic about it?

 

[snowhead]

but I'm assuming wiring can't have been of same period unless floor boxes and dado trunking wre popular back then??

Yes they were.

 

[putalightuponce]

What is tragic about it?

Without going into the extent of the issues with the install, I felt like I should be giving the guy a 'with my deepest sympathy' card along with the report.

 

[putalightuponce]

It's not going to be 0 mohm L-E in reality,because if it was the OCPD would operate assuming it is of the correct rating. More likely it is N-E and you are getting the reading through connected loads.
Did you test the circuits with both L and N of each circuit disconnected from the DB? If so are you certain the correct N was disconnected with the associated live?
It's very common for neutrals to be almost impossible to ID for each circuit if they are not in the correct order in a crammed DB without major disturbance,a mistake in identifying the correct N for a circuit will result in low IR readings if the correct N is not disconnected. Another common complication is more than one N for a circuit in different terminals,with the same result.
If it is apparent that neutrals cant easily be ID'd for disconnection an option to verify satisfactory IR is a global test with the incoming N isolated from the DB. Some frown on this method but they tend to be people who sit at keyboards passing judgement having never actually carried out an EICR in a real working environment.

This sounds like quality advice to me. Thanks wirepuller, I think you're on to it!

 

[telectrix]

most interesting point is finding out that they have electrickery in chester. lol.

 

[nickblake]

If you are getting a 0Mohm reading, then you then need to do a Low Ohm reading to find out exactly what the resistance is between the conductors.
With some experience, you can then take an educated guess as to what the link is between the 2 conductors - a neon, a PIR switch, a lamp etc.
If it is 0 ohms, then it will be a dead short, but you are getting a reading of less than a million ohms, so could be pretty much anything connected, or maybe nothing between the conductors (insulation breakdown).
Depending on your meters accuracy, the reading could be as high as 999,999 ohms, so further testing is required to find , or indicate, the true reading and cause.

may not be on an insulation test its a low insulation reading , if it was a dead short as has been said the Protective device would have operated , the problem is more likely to be a light thats not been disconnected or even water in a light fitting

 

[Plonker 3]

What was the earthing system?
What was the IR between N-E?
Did you disconnect the N or CPC at the DB?

 

[putalightuponce]

most interesting point is finding out that they have electrickery in chester. lol.

No, no, no - job was in London :smile5:
Off topic, but I got asked about an outside light in Chester a while back; I said I could do it but I wasn't gas safe.

 

[Knobhead]

As per usual, no actual figures.

I was under the impression that if a reading was <1MΩ the meter gave a reading in KΩ. I must be mistaken.

What I find annoying is the OP seems willing to condemn a system when he clearly hasn’t tested correctly.