Does anyone have a list of expected Insulation Resistance test results?

[HappyHippyDad]

I was just about to say all that!

 

[Lucien Nunes]

From somewhere I have in mind a figure of 110pF/m L-CPC for 2.5 T+E. That would give 8mA/km at 230V 50Hz discounting stray capacitance to the outside of the cable. Say 1-2mA max per full roll of cable no matter how installed, so I don't think it's a major consideration in basic LV installations. At high frequencies and voltages obviously it's a different kettle of fish.

 

[Marvo]

I'm not sure either of the actual figures offhand I'd need to dig up a chart that will be in a real book made of paper somewhere but I'd agree it's not a major consideration in a domestic installation, it was more thinking out aloud.

I wish there were more of these threads TBH, I know it takes some balls to start them but from what I've seen around the forum there's a lot of guys not understanding what test results are actually indicating and how to interpret them. I can see in another few years that with the lack of education depth that's evident it will be dumbed down to go/no-go tests only and if it fails you make a token effort to localise and just replace the entire suspect section.

**Edit** My comments aren't aimed at you either happyhippydad, I hope it didn't sound that way..

 

[Knobhead]

It’s a pity the method of calculating minimum IR isn’t in the regs now.

 

[HappyHippyDad]

I'm not sure either of the actual figures offhand I'd need to dig up a chart that will be in a real book made of paper somewhere but I'd agree it's not a major consideration in a domestic installation, it was more thinking out aloud.

I wish there were more of these threads TBH, I know it takes some balls to start them but from what I've seen around the forum there's a lot of guys not understanding what test results are actually indicating and how to interpret them. I can see in another few years that with the lack of education depth that's evident it will be dumbed down to go/no-go tests only and if it fails you make a token effort to localise and just replace the entire suspect section.

**Edit** My comments aren't aimed at you either happyhippydad, I hope it didn't sound that way..

No it didn't Marvo :smiley2:

But I think you're right. It's a bit like the 'painting by numbers' example that is going around... Test at 500V if above 2 then ok, if between 1-2 then investigate, if below 1 then fail. It's frustrating not having a deeper understanding of Insulation Resistance Testing but I assume (without going too much into it!!) this is looked at in greater depth in 2365 or 2330 (I will do it one of these days!).

 

[shanky887614]

No it didn't Marvo :smiley2:

But I think you're right. It's a bit like the 'painting by numbers' example that is going around... Test at 500V if above 2 then ok, if between 1-2 then investigate, if below 1 then fail. It's frustrating not having a deeper understanding of Insulation Resistance Testing but I assume (without going too much into it!!) this is looked at in greater depth in 2365 or 2330 (I will do it one of these days!).

nope its not covered more in depth in 2330 and i assume 2357/2365

 

[happysteve]

2365 (and by implication 2357): nope, not so much, unfortunately. Doing 2365 L3 unit 303 "fault diagnosis and rectification" right now. Lots of useful stuff in there, but "typical IR readings for certain conditions" ain't in there. Too many variables, I guess. Just one of the (many) things you get a sense for and pick up on the job.

 

[Simonslimline]

The only questions you will get regarding IR tests will ask if a reading complies with BS7671 or not. Questions regarding what steps to take before carrying out the test are also in one of the units. 2357 knowledge units definitely don't go in to depth on the subject.

Interesting thread by the way, I have definitely learned something from it.

 

[Richard Burns]

The only other thing is when measuring through neons and you get 516k ohms or 100-250 kohms for newer ones, this may come up in fault finding tests.

 

[driverman]

How long is a piece of string, every situation will be different, you can only give a aprox readings. example, pure water is a insulator, but due to impurities, it conducts.....so southern hard water, will conduct better then northern soft water

Re How long is a piece string.....it is twice as long, as it is from the center to one end.........simples!

 

[PEG]

Also,the other problem with compiling a list of prescribed IR values,and attributing them to possible known items,is without further inspection,you would still not know the reason. For example,one specific IR value could be an electrical component,damp or a dead mouse...which means listing the values of ALL the deceased mammals,molluscs and invertebrates we find forming part of a circuit ...:stooge_curly: