Weird test results - help!?

[The General]

I'm a new sparky, in the process of doing two jobs so i can get assessed by NICEIC.

Thought i'd start with a (straightforwards!?) swap of my old C/Unit at home for a nice new 17th Ed one.
All went fine, but now I'm struggling with the certication because the test results are not as expected!
(Or at least, not as easy as it seemed to be when we did our training courses....)

Lighting circuit - insulation resistance tests ought to be >2000Mohms right? (or max on test equip)
my figures range from 27Mohms to 237MOhms, but nowhere near as high as it should be.
[Have taken out all lightbulbs, switched all switches, and measuring across line/earth at c/unit]
As far as I'm aware, nothing else connected to this circuit (i.e. shavers/fans) as it's downstairs lights, and yes, I have taken the bulb out on the 1st floor for the 2-way switched stair light!:thinking:

any ideas? did I forget something obvious? PLEASE let it be something daft, and not something serious!!?

or, are these figures acceptable even if not as high as they ought to be? In which case, panic over.

many thanks!

 

[robsparky1975]

if the wiring is quite old then you might well not get >2000m ohms

 

[Dunc]

Do you have mains powered smoke alarms or a TV amplifier on the lighting circuit? To be perfectly honest 27M ohms is a substantially higher figure then is required to be satisfactory in the eyes of the regs. Also look for outside lights or damp walls. What are the readings between L and N? Do the test at 250V (if you have the ability to on your tester), if the reading is 0M ohms then there is still a load on the circuit somewhere.

 

[The General]

if the wiring is quite old then you might well not get >2000m ohms

Definitely old wiring - at least 25-30yrs old.
from what others are saying sounds like these results are still acceptable - so happy days!

thanks!

 

[The General]

Do you have mains powered smoke alarms or a TV amplifier on the lighting circuit? To be perfectly honest 27M ohms is a substantially higher figure then is required to be satisfactory in the eyes of the regs. Also look for outside lights or damp walls. What are the readings between L and N? Do the test at 250V (if you have the ability to on your tester), if the reading is 0M ohms then there is still a load on the circuit somewhere.

no TV amp (anymore - there was!) no smoke alarms. Figures were similar for L/E, L/N and E/N.
You're right about the outdoor light, one is quite corroded, and results jumped up by appx 100MOhms when I removed it!

cheers for advice about doing 250V test, will give it a go.
Happy if the results are acceptable anyway.....

 

[malcolmsanford]

I'm sorry I'm normally a placid old lad, put me in a corner with a cup of horlicks and a good book and i'm a ----- cat but I have to say this ...............

Your getting results on an IR of 27-237 Mohms and your worried. Now this job is for your assement, and so after this, when you pass as I yet to know of someone that is warm and still breathing fail, you are going to be working in someones home and charging them I no doubt for your competancy and skills ......................I'm going to have a lie down now and take my pills

 

[hasel5]

Results are acceptable What you need to remember you are not in a classroom environment

 

[The General]

Fair point guys - it's just that on the courses they never say "...but the real results you'll get are....." there's just this expectation that everything will be perfect/by the book!!

I'll stop worrying....

cheers all.

 

[hasel5]

good and remember the light does go off in the fridge when you shut the door

 

[Dunc]

no TV amp (anymore - there was!) no smoke alarms. Figures were similar for L/E, L/N and E/N.
You're right about the outdoor light, one is quite corroded, and results jumped up by appx 100MOhms when I removed it!

cheers for advice about doing 250V test, will give it a go.
Happy if the results are acceptable anyway.....

Sounds like damp then, strip back the cable and fit a new light, that might solve the issue altogether.

Just want to add as you're obviously a touch green the reason for suggesting testing at 250V between L and N. When doing PIRs i always do initial tests at 250V. This is a cautionary measure which allows for the possibility of equipment still being plugged in to the system that you may not know about. Tests at 500V can damage electronic equipment whereas 250V will not as it's close to the operating voltage of single phase UK equipment. If the tests come back as >99.9M ohm (that's the reading my Megger 1553 gives) then i re test at 500V and record those reading on the PIR (or EIC if changing a consumer unit).