Testing Thoughts

[mackatoon]

Hi guys, a bit of advise needed if you can help. So i was doing an EICR at a family members property they own and rent out. Its an older property with only a socket or 2 in each room. I could see straight away that the sockets were all overloaded with heavily filled extension leads with double plugs etc

So i ran continuity, R1 + R2s, Ze, PFE, Zs tests with no issues. I started to run the Insulation resistance tests @ 250v which most circuits passed with no issues apart from the Ring Main Sockets which. I got a >999 for Neutral to Live but I got a low reading of 112 ohms for Live to Earth. For 500v I got a measurement of 600 ohms Neutral - Live and 120 ohms for Live - Earth. A couple of the other circuits also struggled at 500 volts. I measured connected to earth bar so not sure if i should go back and measure the cables direct to see if that helps.

What would your thoughts be on the matter. Rewire? for the sockets at least? Or any suggestions. Maybe I'm missing something, i mean i don't know everything (Every day is a school day )

Hate the thought of saying to the family member that they need to spend money on a rewire but i know i need to think of Safety first.

Cheers Guys

Andy

 

[westward10]

I assume you mean meg ohm. If so 120 meg ohm is not low it is fine.

 

[timhoward]

Very different results at 250v and 500v with N > L suggests a surge protected extension lead plugged in which sounds plausible from your post.
Was also going ask about units, as 120 ohms is roughly 2 amps current (230v/120 ohms)- instant RCD trip (if there is one).

 

[mackatoon]

I assume you mean meg ohm. If so 120 meg ohm is not low it is fine.

No not Mega Ohm mate, as i know that would be ok. Well under the >999 that my Megger tester would indicate as successful.

Thanks for the reply though, appreciated

 

[mackatoon]

Very different results at 250v and 500v with N > L suggests a surge protected extension lead plugged in which sounds plausible from your post.
Was also going ask about units, as 120 ohms is roughly 2 amps current (230v/120 ohms)- instant RCD trip (if there is one).

I was thinking this but wouldn't i have got a low result with the 250 volts? I mean i asked the tenant where every plug was so i thought we cleared them all. Bloody nightmare EICRs when you have messy tenants

I appreciate the reply.

Andy

 

[Pete999]

Hi guys, a bit of advise needed if you can help. So i was doing an EICR at a family members property they own and rent out. Its an older property with only a socket or 2 in each room. I could see straight away that the sockets were all overloaded with heavily filled extension leads with double plugs etc

So i ran continuity, R1 + R2s, Ze, PFE, Zs tests with no issues. I started to run the Insulation resistance tests @ 250v which most circuits passed with no issues apart from the Ring Main Sockets which. I got a >999 for Neutral to Live but I got a low reading of 112 ohms for Live to Earth. For 500v I got a measurement of 600 ohms Neutral - Live and 120 ohms for Live - Earth. A couple of the other circuits also struggled at 500 volts. I measured connected to earth bar so not sure if i should go back and measure the cables direct to see if that helps.

What would your thoughts be on the matter. Rewire? for the sockets at least? Or any suggestions. Maybe I'm missing something, i mean i don't know everything (Every day is a school day )

Hate the thought of saying to the family member that they need to spend money on a rewire but i know i need to think of Safety first.

Cheers Guys

Andy

Had you unplugged everything before you started testing IR
? what MFT are you using. parallel earth paths may be a clue, were there any hard wired load ie boiler or heaters in circuit when you tested, what were you testing L /E N\E L/N? Daft question but was the power OFF and isolated? was the Main Earth dissed from the MET,was the test a global test?

 

[westward10]

No not Mega Ohm mate, as i know that would be ok. Well under the >999 that my Megger tester would indicate as successful.

Thanks for the reply though, appreciated

As in #3 are you sure it is ohms.

 

[timhoward]

I was thinking this but wouldn't i have got a low result with the 250 volts? I mean i asked the tenant where every plug was so i thought we cleared them all. Bloody nightmare EICRs when you have messy tenants

I appreciate the reply.

Andy

EDIT - you said >999 Mohm L-N at 250v and 600 ohms L-N at 500v didn't you. So that does fit. The surge protector probably kicked in. For now I'd forget this and focus on the L-Earth which is concerning.

The hard thing is deciding when it just becomes FI and a new piece of work.
I'd probably do two more things as part of an EICR -
1) Remove cpc's from earth bar and try again.
2) Then break the ring somewhere and test each leg.
If same with cpc's removed (so it's a local circuit issue) and if one leg is clear you at least have a clue it's solvable.
Might just be socket screw chafing/touching a live.

 

[mackatoon]

EDIT - you said >999 Mohm L-N at 250v and 600 ohms L-N at 500v didn't you. So that does fit.

So it really is that bad. Wow.
The hard thing is deciding when it just becomes FI and a new piece of work.
I'd probably do two more things as part of an EICR -
1) Remove cpc's from earth bar and try again.
2) Then break the ring somewhere and test each leg.
If same with cpc's removed (so it's a local circuit issue) and if one leg is clear you at least have a clue it's solvable.
Might just be socket screw chafing/touching a live.

Cheers for the advice. Really appreciate it. I'll go back and try what you suggested.

Andy

 

[westward10]

Was the test carried out with line and neutral connected together.

 

[mackatoon]

Was the test carried out with line and neutral connected together.

I tried 3 lead and was still getting the low result

 

[westward10]

I tried 3 lead and was still getting the low result

What do you mean by three lead.

 

[LastManOnline]

Cheers for the advice. Really appreciate it. I'll go back and try what you suggested.

Andy

Carrying out IR tests is the single biggest challenge in doing an EICR. Testing inevitavly starts with very low resistance readings. We then progressively "discover" the accessories/appliances which we actually did, nt see and disconnect in our initial "visual". Its part of the learning curve

 

[westward10]

I think people worry too much over line to neutral readings, they are not necessary. Connect line to neutral and IR to earth, I do hundreds of these a week and nine times out of ten it is fine.

 

[LastManOnline]

I think people worry too much over line to neutral readings, they are not necessary. Connect line to neutral and IR to earth, I do hundreds of these a week and nine times out of ten it is fine.

In fact the emphasis on insulation res. testing for EICRs needs reviewing in my view. It's crucial in new builds and rewires. But for EICR,s the fixed wiring system is the least vulnerable aspect of a 5 year old electrical installation.Focus instead should be on an experienced visual check of the entire installation and testing of all safety devices. If a visual confirms no structural changes/renovations have taken place than an IR test to earth on 250 volts iss sufficient

 

[Pretty Mouth]

I started to run the Insulation resistance tests @ 250v which most circuits passed with no issues apart from the Ring Main Sockets which. I got a >999 for Neutral to Live but I got a low reading of 112 ohms for Live to Earth. For 500v I got a measurement of 600 ohms Neutral - Live and 120 ohms for Live - Earth. A couple of the other circuits also struggled at 500 volts.

@mackatoon there's something not right here. I don't see how you can be getting those results from an IR test.

IR tests return results in meg ohms. 1 meg ohm = 1,000,000 ohms. 120 ohms would show a reading on your meter of 0.00012 meg ohms. Is that really the reading you got at 500V? My meter only has a resolution of 0.01 meg ohms for IR tests.

I suspect, as @westward10 has suggested, you are confusing meg ohms for ohms.

 

[DPG]

I tried 3 lead and was still getting the low result

Can you clarify this, bearing in mind you are doing IR tests.

 

[7029 dave]

If possible could you get a picture of the test results.

 

[timhoward]

In addition to the logic above which I agree with, it was mentioned that R1+R2 was carried out and was ok, and in my head that simply can't be the case if there's really 120 ohms in parallel between R1 and R2, even at the much lower voltage that test uses. (Might be red herring but was R1+R2 done at board or a socket, and if a socket are you sure everything properly re-terminated)

More generally - it's really easy to get increasingly stressed and for rational judgement to go out of the window when IR tests do strange things. Been there plenty of times! I think it was @westward10 who told me once the results were only getting worse each time due to the increased sweat on my fingers affecting the resistance!
New day, cup of tea (solves most electrical problems) and calmly start again I reckon. Please do report back, you have a bunch of us interested now!

 

[Dartlec]

Are there any fuse spurs with old neons in? They can often show up poor IR results - as can extension leads with neons (not so much the more modern LED ones).

But the key is to approach it calmly and if getting odd readings try to isolate it.

If there are only 1-2 sockets per room and tenant is using lots of extension leads then a rewire is probably advisable at some point (assuming the wiring is not recent and just stingy with sockets), but that's very different from being necessary on an EICR.