borrowed neutral/assessment

[rins]

hello everyone

new to the forum, been viewing for a while but 1st post.

anyways ive got my assessment coming up for domestic installation through elesca. however during the process of upgrading a very old fusebox into a shiny new consumer unit i was presented with a shared/borrowed neutral on the lights upstairs, only way of rectifying this was to put both downstairs and upstairs lighting circuits onto same mcb, question is do i need to sort this problem before my assessment or simply put it on my certificate in the box stating what the problem is. assessment is only a cu change, also got a r1+r2 on rfc reading of 29.9, so checked every socket on ring thinking maybe a earth conductor may of been loose or missing but were all present and correct any ideas why this could be? r1 was fine r2 was fine and rn was also ok, any help would be great thanks

 

[Andy™]

if they are on the same MCB then its one circuit and nothing to note. after all, they were originally on the same fuse and youve just kept that the same...

 

[rins]

Thanks for quick replies lads firstly yep i did the figure ov 8 incoming line to outgoing earth, incoming earth to outgoing line used my metrel easitest mft, placed my plug in tester in every socket and was getting readings ov 29:9

R1, 0.1

R2, 0.1

RN, 0.2

thanks also for pointing out thats its one circuit i just needed that confirmed gotta get things bang on for assessment

 

[Barx]

Well them readings are wrong for a start. Rn should be pretty much same as r1. R2 should be either 1.67 or 2.5 times r1 depending if it's 1.5 or 1 mm earth.

Sent from my Desire Z

 

[Andy™]

Thanks for quick replies lads firstly yep i did the figure ov 8 incoming line to outgoing earth, incoming earth to outgoing line used my metrel easitest mft, placed my plug in tester in every socket and was getting readings ov 29:9R1, 0.1

R2, 0.1

RN, 0.2

thanks also for pointing out thats its one circuit i just needed that confirmed gotta get things bang on for assessment

you should have a reading to 2 decimal place... and R2 should be higher than R1 & Rn

 

[chrisg1979]

Alternatively you could put the 2 lighting circuits on their own MCB's (same RCD) and stick a borrowed neutrals sticker on the cu, then at least they can still be individually isolated.

 

[Andy™]

i wouldnt do that. they are electrically connected. if you isolate one, you may end up with a live neutral on the other.

 

[SLIPSHOD & SLAPDASH]

Although its common for r2 to be picking up an earth through pipework, appliances etc and be lower than the others

 

[chrisg1979]

i wouldnt do that. they are electrically connected. if you isolate one' date=' you may end up with a live neutral on the other.[/quote']Would tend to agree, just putting forward an alternative.

 

[rins]

Sorry got that wrong didnt have my results on me

R1, 0.2

R2. 0.4

RN, 0.2

any better, i havnt done much testing just trying to suss things out and rather stuck really

 

[Barx]

Hmmmm, suss.....

Anyhow's, as mentioned above reading should be 2 decimal places. But that aside. IF those are the reading AND all sockets are on the ring AND all connections to the faceplate are good then I would say..... 'you didn't zero your socket lead before testing'. Other than that I don't see how you could get the results you did.

Sent from my Desire Z

 

[rins]

Thanks guys i,ll keep working on it got many years experience in installing got 2330 and 17th too just not much testing, thinking of going on the 2392 in febuary cheers for replies

 

[Barx]

No worries mate. SAme as anything really. You need to understand it first. You could bake bread for 20 years, but unless you taste it you don't know if your doing it right.

That probably makes no sense but it popped into my head for some reason.

 

[SPECIAL LOCATION]

Sorry got that wrong didnt have my results on me R1, 0.2

R2. 0.4

RN, 0.2

any betterhaven'tavnt done much testing just tryingSeusssuss things out and rather stuck really

Have you ever considered calculating approximate lengths for r1 r2 rn values..

{R1, R2 etc are NOT r1, r2 etc.. by the way!}

Using table 11 page 182 green OSG (or table 9A page 166 red OSG.)

Assuming r1 & rn are 2.5mm then 0.2ohms is approx 27m of cable

and assuming r2 could be 1.5mm or 1.0mm then 0.4ohms could be either

22m if 1.0mm or 33m if 1.5mm CSA?

Or somewhere in between if a mix of sizes used in the property.

Do these sound feasible lengths for the cable runs probable at the installation?

Assuming no poor joints or damaged cable?.

 

[sellers]

If this high reading is on just one socket try taking the reading at the terminals behind

 

[SPECIAL LOCATION]

Why are your values only to a single decimal place?

If I were assessing these results I would be asking why you don

 

[rins]

Those lengths could be about right because the whole house upstairs, downstairs and kitchen form 1 ring it has a total of 10 socket outlets on, thanks for that iam back there tomoro (empty house) so i,ll check and retest again, til i get it right thanks again

---------- Post Auto-Merged at 22:28 ---------- Previous post was made at 22:15 ----------

Thanks special location i will get on that tomorrow, infact thanks everybody for the help this testing game will hopefully get easier with practice

 

[froria]

If this high reading is on just one socket try taking the reading at the terminals behind

This is a deff possibility.

I was at a property and did a loop test at a socket and it was around 60 ohm took at the back of the socket and bingo bango all is good just a faulty socket outlet

 

[chrishaworth]

It's back to the RCD distortion of loop readings. Even the exalted members on the IET site can't explain it, but it is common. Take DC readings across the RCD, if they read close to 0, then calculate the Zs, otherwise replace the RCD.

Cheers