End to end confusion

[bulmer]

Would be grateful for a little help and guidence with a bit of test that i've been doing this morning.

RFC end to end continuity results were as follows - r1 0.64 ohms rn 0.62 ohms r2 0.82 ohms.

Was happy with my r1 and rn results, but then when I did my r2 it through me a little as I was expecting around 1.05 ohms as the cable is a 2.5mm/1.5mm.

I took every socket off the wall a redid the connections up tight, just incase both the line and neutral were loose or badly made. The results were still the same. Is it possible that if you had a dodgy connection somewhere on both line and neutral, then the readings could still be so close?

So my thinking is this, what are the chances of there being a high resistance joint on both the line a neutral causing them to have high readings in relation to r2.

 

[springcrocus]

I would guess that its more likely a parallel earth path bringing your r2 down.

 

[bulmer]

I would guess that its more likely a parallel earth path bringing your r2 down.

Would this need to be identified on my cert, even though my circuit complies.

 

[sparkytim]

No

 

[batty]

Is the immersion on the ring main?

 

[Andy™]

could be dodgy connections?

 

[PC Electrics]

Is it possible from what you could see that the ring has been extended at some point, but the earths were bunched together at the point of extension whilst the L & N were extended properly? In other words, you've got a ring on L & N but a figure of 8 on cpc.

 

[tom1]

would cpc twisted together in the sockets have an effect?

 

[NozSpark]

The only time I have had a problem with a low r2 was in my brothers house which has 2 x bathrooms, both supp bonded. (continuous copper piping throughout)

 

[bulmer]

Is the immersion on the ring main?

No immersion at the house

[quote name='Andy

 

[sparkytim]

As your R1 and RN are much the same then it is unlikely you have a problem with LOOSE connections on them, so parrallel earth path with CPC is likely.

This is quite common and nothing to worry about, is the boiler wired off FCU on the ring?

This would provide a parallel path thru boiler and pipe work.

Your readings are quite acceptable for a real working installation as they rearly work out exactly as they should on paper.

 

[Mark2spark]

I've come across a good few houses with a 4mm taken off the ring nearest socket to bathroom to provide the supp, and occasionally it's been discovered off a JB under the floorboards in the under the bath vincinity.

Parellel earth is where my quid is, although I like PC electrics offering as well.

I give up sometimes trying to work out readings when they are strange. As long as there's continuity jobs done pretty much. Just record it and move on.

 

[a1spark]

On Zs readings I agree, butWould parrallel paths come into play when doing end to end resistance measurements with conductors isolated from the MET and all equipment disconnected off the ring ?

 

[springcrocus]

We don't know if this is a new install or a check of the existing installation.

One possible scenario (on an existing):-

Cables in old-fashioned conduit and back boxes bonded to the earth terminal on the socket outlet plate - the conduit could have a lower resistance than the cable...

 

[tom1]

We don't know if this is a new install or a check of the existing installation.One possible scenario (on an existing):-

Cables in old-fashioned conduit and back boxes bonded to the earth terminal on the socket outlet plate - the conduit could have a lower resistance than the cable...

think thats what happened the other day on my readings

L 0.33 N 0.32 E0.19

 

[a1spark]

Springcrocus ,I agree yes, on a mixed wiring system this could be the reason for these readings.

Tom. Yes ,as i recall you did indeed have such a mixed wiring system recently didnt you ?

 

[tom1]

Springcrocus ,I agree yes, on a mixed wiring system this could be the reason for these readings.Tom. Yes ,as i recall you did indeed have such a mixed wiring system recently didnt you ?

yer it was a bit unconventional, on ther cert i have type of wiring A/B,

and also, may be not in this case, but if its in singles in places is it more likely that the cpc can be can have a csa of 2.5

 

[a1spark]

Yes thats a possibility too !

 

[bulmer]

Is it possible from what you could see that the ring has been extended at some point, but the earths were bunched together at the point of extension whilst the L & N were extended properly? In other words, you've got a ring on L & N but a figure of 8 on cpc.

Been back to this one today and its exactly as this. Took me an absolute age to move the big old sideboard they had hiding the socket that the ring had been extended from.

Thanks for all your input guys, appreciate it:coffee