Insulation resistance problem

[Midwest]

Sparky1508, some of the replies you don't like, are probably not helped by the fact, that you do not indicate your qualifications or competency in your profile. You'll see members have gone there to have a look, including me. If you do display them, you might find the negatives a little less shared.

I find fault finding quite taxing, where others on here find it enthralling. As well as the many other helpful suggestions, may I suggest (following safe isolation of course) is removing (not disconnecting) all face plates, too see how many cables you have at each point. This might identify any errant spurs etc, you may not be aware of and indeed might reveal any possible faults, if it is a fault at all.

As davesparks finished his sentence with a comma, you make wish to take up his job offer or mentoring, as he does have a compassionate side which he tries to conceal at times, but indeed has a realm of experience to offer.

 

[sparky1508]

I was hoping to get help on here as I've seen in many posts he's very knowledgeable and always gives sound advice. I cant seem to find how to put my info on my profile but this is what I now have.
City and guilds 2393-10
City and guilds level 3 2382-15 regs
City and guilds level 3 2394 and 2395
City and guilds 2377-22.
All I want to do is learn that's why I'm on here and at home testing my own stuff before I go out and do it for real.

 

[sparky1508]

I am not saying that those situations wouldn't cause a fault, i am saying that the test results you have do not indicate that type of fault.

You have made no mention of a dead short in your posts, the lowest resistance I think you have quoted is 0.01M ohms, which is 10,000 ohms, simple maths will tell you that this is will not trip an RCD. A dead short would be in the region of zero ohms.

Nobody knows why they have a low IR reading until they have found the reason, my issue is that you don't understand what the test result actually means in real world terms.

Thanks dave, I realise now what you are saying but I was thinking if a conductor was just very close to another but not actually touching somewhere would that not be similar to having bad insulation or am I still being simple.

 

[bigspark17]

Cooker hood.?

 

[davesparks]

Thanks dave, I realise now what you are saying but I was thinking if a conductor was just very close to another but not actually touching somewhere would that not be similar to having bad insulation or am I still being simple.

It would have to be very very close for it to have a measureable resistance at 500V.

It would just act as a capacitor

 

[tony mc]

Do you have a alarm system connected to the RFC via a spur or a RCD FCU or socket?

Once you start to test in a methodical way as Davesparks as suggested things will become far more clear,I would definately mark the sockets once eliminated dont try and just remember them as you quickly get confused.

Lets hope you tested L/N on soft test on 250 v scale for obvious reasons.

I would suggest access to a tester which has a KOhm range as when testing on the Meg scale when it gives a 0.00 result you need to switch scale to find out exactaly what the reading is. Many MFT testers dont have a KOhm range !


If you get a very low reading then as a guide you can get a rough idea how far away the fault is using maths and cable resistance values!

Let us know how you get on lets hope its not unaccessible joint boxes!

 

[sparky1508]

Thanks for that. I have a fluke 1654b, not sure I it has a Kohm setting but will look into it.

 

[sparky1508]

Do you have a alarm system connected to the RFC via a spur or a RCD FCU or socket?

Once you start to test in a methodical way as Davesparks as suggested things will become far more clear,I would definately mark the sockets once eliminated dont try and just remember them as you quickly get confused.

Lets hope you tested L/N on soft test on 250 v scale for obvious reasons.

I would suggest access to a tester which has a KOhm range as when testing on the Meg scale when it gives a 0.00 result you need to switch scale to find out exactaly what the reading is. Many MFT testers dont have a KOhm range !


If you get a very low reading then as a guide you can get a rough idea how far away the fault is using maths and cable resistance values!

Let us know how you get on lets hope its not unaccessible joint boxes!

Thanks
No alarm connected.
Will do methodical as Dave suggested.
Forgive me for this but the only reason to test on 250v as far as I am aware is to protect sensitive equipment but I had every plug disconnected from the sockets and had nothing left connected. I know I don't need to unplug but just went round and unplugged everything anyway. Is there another reason I should test on 250v?

 

[telectrix]

Thanks
No alarm connected.
Will do methodical as Dave suggested.
Forgive me for this but the only reason to test on 250v as far as I am aware is to protect sensitive equipment but I had every plug disconnected from the sockets and had nothing left connected. I know I don't need to unplug but just went round and unplugged everything anyway. Is there another reason I should test on 250v?

you do this so that, even though you think all loads are disconnected there could be one left that you have missed.

 

[sparky1508]

So if there is still a load connected and I test at 250v would my reading be >200 Mohm meaning everything is good.