Hi Guys

[Niblok]

just done Insulation Resistance Test on ring main, result was 300
have tested each cable separately got 500 on all, then tested as a one long radial got 500 then tested as ring again got 300

the ring has got 8 sockets on it and is not what i would consider long
has not been in use for about a year

300 not a bad result but not what i was expecting
new to this so i think it me doing something wrong

all help and criticism welcome

 

[securespark]

What's the max. reading in M Ohms on your meter?

 

[Taylortwocities]

300 what?

Eskimos? Polar Bears?

Ohms
Megohms??

 

[Niblok]

500 Megohms

 

[Taylortwocities]

500 Megohms

Thats a pretty good result. Was this testing at 500vDC?
Do you have a problem then?

 

[sparky1505]

Hi there, if you are testing the inulation resistance live to earth, neutral to earth, live to neutral or combined live + neutral to earth and in each test getting readings >300Mohm then this is a good result.

 

[tonyelectric]

Well my one year old Megger MFTsomethingorother only goes to 299MOhm at 500V - yep it's a good result

My much older hand cranked Megger which has just been calibrated can't make infinity at the moment because of the damp atmosphere (its fine if its been indoors for a while!) best I can get at full pelt is between 1000M and INF- According to Megger mine which about 18" long and cased in mahogany was made in 1924 and it still passes calibration - great stuff

 

[Taylortwocities]

And you will get a lower IR reading as a ring as you are sort of paralleling up the conductors.

The difference between the radial and the ring results will equate something like the R1+R2 ring final calculations (that you love) as a result of the r1 & r2 end-to-end measurements.

 

[Niblok]

yes it was tested at 500v i just was expecting a result of 500 megohm

thanks to you all


mahogany megger wood love to see that, beware the wood worm

 

[londonboy]

Do have a copy of GN3 (Guidance Notes 3)?

Its very detailed and explains things step by step, it might help you understand what the IR measurement actually is

 

[tonyelectric]

mahogany megger wood love to see that, beware the wood worm [/quote]

This link will show you one identical to mine

http://www.museumoftechnology.org.uk/nimages/A0582_tn.jpg

its a series 1, they actually kept this model in production until the early 80s with the mahogany casing, excellent basic bit of kit for the bench but a bit heavy to carry around at 12Kg