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