Insulation Resistence on ring main

[Dannydigger]

Hi Guys,

I am absolutely baffled at the moment as to why i cannot get the correct reading for insulation resistence when Im testing the line/neutral on the ring main. I have made sure everything is unplugged, disconnected the neutral from the bar and allgator clipped to my test lead. When I press test, it goes through the relevent steps and comes back with 0.00

I have also tried this on my ring main at home and still get the same reading for line/neutral.

I get >1000 when I do CPC/Neutral and all other Circuits give correct readings of >1000

Its just the Line/Neutral that is stumping me, any help is greatly appreciated

 

[Dannydigger]

I have just finished my course but just wanted clarity as I thought everything was disconnected

 

[Guest77]

I have just finished my course but just wanted clarity as I thought everything was disconnected

Yeah fair enough, in future let people know you are a trainee or inexperienced and it will make our job easier, you see I was thinking you were an experienced spark because you are tesing work in someones home so questioned the original question you asked and thought you were having a laugh with us, now I know your inexperienced it all makes sence, there is still something connected Danny, you will have to investigate the circuit further.

 

[drzsta]

one thing alot of people forget is that anything with a NEON indicator will give you a dead short L-N.
Stuff like FCU's,Cooker switches etc etc....

 

[NDG Elecs]

I find neons normally give around 0.25 on 500V rather than 0.00. There is defo something connected somewhere, that's for sure.

 

[ruston]

Lol a USB socket?

 

[NDG Elecs]

Lol a USB socket?

Megger gave this guidance out not long back mate:



Not the full gumph but basically saying switched mode power supplies (usbs) normally read 0.02 on IR tests.

 

[ruston]

Thanks, but something else for us to look for , especially if there are more than one.

 

[Dannydigger]

My apologies MDJ and also for my outburst. I was getting 0.00 so all neons were off. I have double checked myself now and found a fridge plugged in at the back of a cupboard. My customer had just turned it off by the FCU on the kitchen top.

thanks again folks

 

[NDG Elecs]

My apologies MDJ and also for my outburst. I was getting 0.00 so all neons were off. I have double checked myself now and found a fridge plugged in at the back of a cupboard. My customer had just turned it off by the FCU on the kitchen top.

thanks again folks

Danny, you may do this already, but always test at 250V first to check for loads before whacking 500V through to prevent frying any loads. And always double check all switches and sockets yourself. I ask the customer if there are any sockets that may have been forgotten about, and then five mins later I ask again... It's very easy to forget the odd socket/FCU. A 250V IR test normally finds anything tho

 

[Guest77]

No worries buddy, now we know you the next time you post a question you will get more help and less questioning, welcome aboard fella.

 

[davesparks]

I carried out continuity tests and all came back fine at 0.15

i did minor works and on my certs it asks for I/R on l/n n/e l/e

im assuming my customer hadn't pulled out all plugs as requested as continuity was fine and I also did the crossover test with line and neutral and tested at socket that was replaced.

Thanks again for for the help guys, it's really appreciated

Just because you only have boxes for something's on the MWC it doesn't mean you don't carry out all appropriate tests.

Why are you assuming the customer didn't unplug things? You should be confirming no loads are present before carrying out testing, it is after all your responsibility and your insurance which will have to pay of you get it wrong

 

[NDG Elecs]

Just because you only have boxes for something's on the MWC it doesn't mean you don't carry out all appropriate tests.

Why are you assuming the customer didn't unplug things? You should be confirming no loads are present before carrying out testing, it is after all your responsibility and your insurance which will have to pay of you get it wrong

Unfortunately, we live in a tick box culture... I often leave boxes unticked if not entirely relevant/needed. The model forms give out the minimum requirements.

 

[Lucien Nunes]

Some suggestions for the OP about reporting and understanding IR test results:

1. When giving figures, state the units. With IR we can generally assume megohms but not always. Saying the test result was 0.00 or 100 is like me telling you my car is 6 old or that I need a cable 25 long.

2. If the result is very low, recheck with a multimeter or continuity tester to see how low. 0.00 MΩ could still be 5 kΩ, which is thousands of times higher than the circuit cable itself.

3. A short-circuit is just that. It isn't a connected load, it certainly isn't a neon (which is completely open-circuit at low voltage), nor does it mean very low IR. The clue is in the name - it means literally a circuit that is completed somwhere short of its proper destination, and for the last century or more the understanding has been that a short has negligible resistance.

4. There is no 'correct' reading for IR although you often know what to expect. The more kinds of circuit and conditions you test under, the less it will seem that >1000 (somethings) makes an ideal reading.

5. Not related to the OP but worthy of mention - 'low' IR is usually symptomless. It's a good way to locate trouble but even 0.05 MΩ L-E which most would consider disastrously low won't trip an rcd. Even 8 kΩ, which an MFT might display as 0.00 MΩ, isn't guaranteed to trip, and N-E you might get away with 0.000001 MΩ (1Ω) before nuisance tripping sets in. Use ohm's law!

 

[markc123]

Unfortunately, we live in a tick box culture... I often leave boxes unticked if not entirely relevant/needed. The model forms give out the minimum requirements.

I've always put a line through any box thats not needed / irrelevant - cert's can be modified by numpties. Won't matter if you have hard copies of the cert, i.e. the tracing paper underneath, but i was always told just incase, make sure every box has at least something in.

 

[ian.settle1]

I'm guessing this is not a brand new circuit so your not obliged to test line/neutral anyway.

Set tester onto continuity and see what reading you have then, it'll probably be a load that you are not aware of.

Please explain why you are not obliged to test it?